1139 lines
42 KiB
C++
1139 lines
42 KiB
C++
// icf.cc -- Identical Code Folding.
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//
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// Copyright (C) 2009-2022 Free Software Foundation, Inc.
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// Written by Sriraman Tallam <tmsriram@google.com>.
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// This file is part of gold.
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
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// MA 02110-1301, USA.
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// Identical Code Folding Algorithm
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// ----------------------------------
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// Detecting identical functions is done here and the basic algorithm
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// is as follows. A checksum is computed on each foldable section using
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// its contents and relocations. If the symbol name corresponding to
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// a relocation is known it is used to compute the checksum. If the
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// symbol name is not known the stringified name of the object and the
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// section number pointed to by the relocation is used. The checksums
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// are stored as keys in a hash map and a section is identical to some
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// other section if its checksum is already present in the hash map.
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// Checksum collisions are handled by using a multimap and explicitly
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// checking the contents when two sections have the same checksum.
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//
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// However, two functions A and B with identical text but with
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// relocations pointing to different foldable sections can be identical if
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// the corresponding foldable sections to which their relocations point to
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// turn out to be identical. Hence, this checksumming process must be
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// done repeatedly until convergence is obtained. Here is an example for
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// the following case :
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//
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// int funcA () int funcB ()
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// { {
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// return foo(); return goo();
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// } }
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//
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// The functions funcA and funcB are identical if functions foo() and
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// goo() are identical.
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//
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// Hence, as described above, we repeatedly do the checksumming,
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// assigning identical functions to the same group, until convergence is
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// obtained. Now, we have two different ways to do this depending on how
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// we initialize.
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//
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// Algorithm I :
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// -----------
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// We can start with marking all functions as different and repeatedly do
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// the checksumming. This has the advantage that we do not need to wait
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// for convergence. We can stop at any point and correctness will be
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// guaranteed although not all cases would have been found. However, this
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// has a problem that some cases can never be found even if it is run until
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// convergence. Here is an example with mutually recursive functions :
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//
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// int funcA (int a) int funcB (int a)
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// { {
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// if (a == 1) if (a == 1)
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// return 1; return 1;
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// return 1 + funcB(a - 1); return 1 + funcA(a - 1);
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// } }
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//
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// In this example funcA and funcB are identical and one of them could be
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// folded into the other. However, if we start with assuming that funcA
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// and funcB are not identical, the algorithm, even after it is run to
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// convergence, cannot detect that they are identical. It should be noted
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// that even if the functions were self-recursive, Algorithm I cannot catch
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// that they are identical, at least as is.
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//
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// Algorithm II :
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// ------------
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// Here we start with marking all functions as identical and then repeat
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// the checksumming until convergence. This can detect the above case
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// mentioned above. It can detect all cases that Algorithm I can and more.
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// However, the caveat is that it has to be run to convergence. It cannot
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// be stopped arbitrarily like Algorithm I as correctness cannot be
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// guaranteed. Algorithm II is not implemented.
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//
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// Algorithm I is used because experiments show that about three
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// iterations are more than enough to achieve convergence. Algorithm I can
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// handle recursive calls if it is changed to use a special common symbol
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// for recursive relocs. This seems to be the most common case that
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// Algorithm I could not catch as is. Mutually recursive calls are not
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// frequent and Algorithm I wins because of its ability to be stopped
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// arbitrarily.
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//
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// Caveat with using function pointers :
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// ------------------------------------
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//
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// Programs using function pointer comparisons/checks should use function
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// folding with caution as the result of such comparisons could be different
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// when folding takes place. This could lead to unexpected run-time
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// behaviour.
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//
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// Safe Folding :
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// ------------
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//
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// ICF in safe mode folds only ctors and dtors if their function pointers can
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// never be taken. Also, for X86-64, safe folding uses the relocation
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// type to determine if a function's pointer is taken or not and only folds
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// functions whose pointers are definitely not taken.
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//
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// Caveat with safe folding :
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// ------------------------
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//
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// This applies only to x86_64.
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//
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// Position independent executables are created from PIC objects (compiled
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// with -fPIC) and/or PIE objects (compiled with -fPIE). For PIE objects, the
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// relocation types for function pointer taken and a call are the same.
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// Now, it is not always possible to tell if an object used in the link of
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// a pie executable is a PIC object or a PIE object. Hence, for pie
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// executables, using relocation types to disambiguate function pointers is
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// currently disabled.
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//
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// Further, it is not correct to use safe folding to build non-pie
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// executables using PIC/PIE objects. PIC/PIE objects have different
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// relocation types for function pointers than non-PIC objects, and the
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// current implementation of safe folding does not handle those relocation
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// types. Hence, if used, functions whose pointers are taken could still be
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// folded causing unpredictable run-time behaviour if the pointers were used
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// in comparisons.
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//
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// Notes regarding C++ exception handling :
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// --------------------------------------
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//
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// It is possible for two sections to have identical text, identical
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// relocations, but different exception handling metadata (unwind
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// information in the .eh_frame section, and/or handler information in
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// a .gcc_except_table section). Thus, if a foldable section is
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// referenced from a .eh_frame FDE, we must include in its checksum
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// the contents of that FDE as well as of the CIE that the FDE refers
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// to. The CIE and FDE in turn probably contain relocations to the
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// personality routine and LSDA, which are handled like any other
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// relocation for ICF purposes. This logic is helped by the fact that
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// gcc with -ffunction-sections puts each function's LSDA in its own
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// .gcc_except_table.<functionname> section. Given sections for two
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// functions with nontrivial exception handling logic, we will
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// determine on the first iteration that their .gcc_except_table
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// sections are identical and can be folded, and on the second
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// iteration that their .text and .eh_frame contents (including the
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// now-merged .gcc_except_table relocations for the LSDA) are
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// identical and can be folded.
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//
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//
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// How to run : --icf=[safe|all|none]
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// Optional parameters : --icf-iterations <num> --print-icf-sections
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//
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// Performance : Less than 20 % link-time overhead on industry strength
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// applications. Up to 6 % text size reductions.
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#include "gold.h"
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#include "object.h"
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#include "gc.h"
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#include "icf.h"
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#include "symtab.h"
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#include "libiberty.h"
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#include "demangle.h"
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#include "elfcpp.h"
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#include "int_encoding.h"
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#include <limits>
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namespace gold
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{
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// This function determines if a section or a group of identical
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// sections has unique contents. Such unique sections or groups can be
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// declared final and need not be processed any further.
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// Parameters :
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// ID_SECTION : Vector mapping a section index to a Section_id pair.
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// IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical
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// sections is already known to be unique.
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// SECTION_CONTENTS : Contains the section's text and relocs to sections
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// that cannot be folded. SECTION_CONTENTS are NULL
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// implies that this function is being called for the
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// first time before the first iteration of icf.
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static void
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preprocess_for_unique_sections(const std::vector<Section_id>& id_section,
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std::vector<bool>* is_secn_or_group_unique,
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std::vector<std::string>* section_contents)
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{
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Unordered_map<uint32_t, unsigned int> uniq_map;
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std::pair<Unordered_map<uint32_t, unsigned int>::iterator, bool>
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uniq_map_insert;
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for (unsigned int i = 0; i < id_section.size(); i++)
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{
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if ((*is_secn_or_group_unique)[i])
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continue;
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uint32_t cksum;
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Section_id secn = id_section[i];
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section_size_type plen;
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if (section_contents == NULL)
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{
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// Lock the object so we can read from it. This is only called
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// single-threaded from queue_middle_tasks, so it is OK to lock.
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// Unfortunately we have no way to pass in a Task token.
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const Task* dummy_task = reinterpret_cast<const Task*>(-1);
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Task_lock_obj<Object> tl(dummy_task, secn.first);
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const unsigned char* contents;
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contents = secn.first->section_contents(secn.second,
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&plen,
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false);
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cksum = xcrc32(contents, plen, 0xffffffff);
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}
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else
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{
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const unsigned char* contents_array = reinterpret_cast
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<const unsigned char*>((*section_contents)[i].c_str());
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cksum = xcrc32(contents_array, (*section_contents)[i].length(),
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0xffffffff);
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}
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uniq_map_insert = uniq_map.insert(std::make_pair(cksum, i));
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if (uniq_map_insert.second)
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{
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(*is_secn_or_group_unique)[i] = true;
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}
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else
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{
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(*is_secn_or_group_unique)[i] = false;
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(*is_secn_or_group_unique)[uniq_map_insert.first->second] = false;
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}
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}
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}
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// For SHF_MERGE sections that use REL relocations, the addend is stored in
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// the text section at the relocation offset. Read the addend value given
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// the pointer to the addend in the text section and the addend size.
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// Update the addend value if a valid addend is found.
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// Parameters:
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// RELOC_ADDEND_PTR : Pointer to the addend in the text section.
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// ADDEND_SIZE : The size of the addend.
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// RELOC_ADDEND_VALUE : Pointer to the addend that is updated.
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inline void
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get_rel_addend(const unsigned char* reloc_addend_ptr,
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const unsigned int addend_size,
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uint64_t* reloc_addend_value)
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{
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switch (addend_size)
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{
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case 0:
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break;
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case 1:
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*reloc_addend_value =
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read_from_pointer<8>(reloc_addend_ptr);
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break;
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case 2:
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*reloc_addend_value =
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read_from_pointer<16>(reloc_addend_ptr);
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break;
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case 4:
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*reloc_addend_value =
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read_from_pointer<32>(reloc_addend_ptr);
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break;
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case 8:
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*reloc_addend_value =
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read_from_pointer<64>(reloc_addend_ptr);
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break;
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default:
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gold_unreachable();
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}
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}
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// This returns the buffer containing the section's contents, both
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// text and relocs. Relocs are differentiated as those pointing to
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// sections that could be folded and those that cannot. Only relocs
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// pointing to sections that could be folded are recomputed on
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// subsequent invocations of this function.
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// Parameters :
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// FIRST_ITERATION : true if it is the first invocation.
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// FIXED_CACHE : String that stores the portion of the result that
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// does not change from iteration to iteration;
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// written if first_iteration is true, read if it's false.
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// SECN : Section for which contents are desired.
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// SELF_SECN : Relocations that target this section will be
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// considered "relocations to self" so that recursive
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// functions can be folded. Should normally be the
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// same as `secn` except when processing extra identity
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// regions.
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// NUM_TRACKED_RELOCS : Vector reference to store the number of relocs
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// to ICF sections.
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// KEPT_SECTION_ID : Vector which maps folded sections to kept sections.
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// START_OFFSET : Only consider the part of the section at and after
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// this offset.
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// END_OFFSET : Only consider the part of the section before this
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// offset.
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static std::string
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get_section_contents(bool first_iteration,
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std::string* fixed_cache,
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const Section_id& secn,
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const Section_id& self_secn,
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unsigned int* num_tracked_relocs,
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Symbol_table* symtab,
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const std::vector<unsigned int>& kept_section_id,
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section_offset_type start_offset = 0,
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section_offset_type end_offset =
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std::numeric_limits<section_offset_type>::max())
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{
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section_size_type plen;
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const unsigned char* contents = NULL;
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if (first_iteration)
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contents = secn.first->section_contents(secn.second, &plen, false);
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// The buffer to hold all the contents including relocs. A checksum
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// is then computed on this buffer.
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std::string buffer;
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std::string icf_reloc_buffer;
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Icf::Reloc_info_list& reloc_info_list =
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symtab->icf()->reloc_info_list();
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Icf::Reloc_info_list::iterator it_reloc_info_list =
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reloc_info_list.find(secn);
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buffer.clear();
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icf_reloc_buffer.clear();
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// Process relocs and put them into the buffer.
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if (it_reloc_info_list != reloc_info_list.end())
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{
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Icf::Sections_reachable_info &v =
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(it_reloc_info_list->second).section_info;
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// Stores the information of the symbol pointed to by the reloc.
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const Icf::Symbol_info &s = (it_reloc_info_list->second).symbol_info;
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// Stores the addend and the symbol value.
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Icf::Addend_info &a = (it_reloc_info_list->second).addend_info;
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// Stores the offset of the reloc.
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const Icf::Offset_info &o = (it_reloc_info_list->second).offset_info;
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const Icf::Reloc_addend_size_info &reloc_addend_size_info =
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(it_reloc_info_list->second).reloc_addend_size_info;
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Icf::Sections_reachable_info::iterator it_v = v.begin();
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Icf::Symbol_info::const_iterator it_s = s.begin();
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Icf::Addend_info::iterator it_a = a.begin();
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Icf::Offset_info::const_iterator it_o = o.begin();
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Icf::Reloc_addend_size_info::const_iterator it_addend_size =
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reloc_addend_size_info.begin();
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for (; it_v != v.end(); ++it_v, ++it_s, ++it_a, ++it_o, ++it_addend_size)
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{
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Symbol* gsym = *it_s;
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bool is_section_symbol = false;
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// Ignore relocations outside the region we were told to look at
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if (static_cast<section_offset_type>(*it_o) < start_offset
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|| static_cast<section_offset_type>(*it_o) >= end_offset)
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continue;
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// A -1 value in the symbol vector indicates a local section symbol.
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if (gsym == reinterpret_cast<Symbol*>(-1))
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{
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is_section_symbol = true;
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gsym = NULL;
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}
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if (first_iteration
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&& it_v->first != NULL)
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{
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Symbol_location loc;
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loc.object = it_v->first;
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loc.shndx = it_v->second;
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loc.offset = convert_types<off_t, long long>(it_a->first
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+ it_a->second);
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// Look through function descriptors
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parameters->target().function_location(&loc);
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if (loc.shndx != it_v->second)
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{
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it_v->second = loc.shndx;
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// Modify symvalue/addend to the code entry.
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it_a->first = loc.offset;
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it_a->second = 0;
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}
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}
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// ADDEND_STR stores the symbol value and addend and offset,
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// each at most 16 hex digits long. it_a points to a pair
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// where first is the symbol value and second is the
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// addend.
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char addend_str[50];
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// It would be nice if we could use format macros in inttypes.h
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// here but there are not in ISO/IEC C++ 1998.
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snprintf(addend_str, sizeof(addend_str), "%llx %llx %llx",
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static_cast<long long>((*it_a).first),
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static_cast<long long>((*it_a).second),
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static_cast<unsigned long long>(*it_o - start_offset));
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// If the symbol pointed to by the reloc is not in an ordinary
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// section or if the symbol type is not FROM_OBJECT, then the
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// object is NULL.
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if (it_v->first == NULL)
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{
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if (first_iteration)
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{
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// If the symbol name is available, use it.
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if (gsym != NULL)
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buffer.append(gsym->name());
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// Append the addend.
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buffer.append(addend_str);
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buffer.append("@");
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}
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continue;
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}
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Section_id reloc_secn(it_v->first, it_v->second);
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// If this reloc turns back and points to the same section,
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// like a recursive call, use a special symbol to mark this.
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if (reloc_secn.first == self_secn.first
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&& reloc_secn.second == self_secn.second)
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{
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if (first_iteration)
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{
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buffer.append("R");
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buffer.append(addend_str);
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buffer.append("@");
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}
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continue;
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}
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Icf::Uniq_secn_id_map& section_id_map =
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symtab->icf()->section_to_int_map();
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Icf::Uniq_secn_id_map::iterator section_id_map_it =
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section_id_map.find(reloc_secn);
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bool is_sym_preemptible = (gsym != NULL
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&& !gsym->is_from_dynobj()
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&& !gsym->is_undefined()
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&& gsym->is_preemptible());
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if (!is_sym_preemptible
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&& section_id_map_it != section_id_map.end())
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{
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// This is a reloc to a section that might be folded.
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if (num_tracked_relocs)
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(*num_tracked_relocs)++;
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char kept_section_str[10];
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unsigned int secn_id = section_id_map_it->second;
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snprintf(kept_section_str, sizeof(kept_section_str), "%u",
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kept_section_id[secn_id]);
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if (first_iteration)
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{
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buffer.append("ICF_R");
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buffer.append(addend_str);
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}
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icf_reloc_buffer.append(kept_section_str);
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// Append the addend.
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icf_reloc_buffer.append(addend_str);
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icf_reloc_buffer.append("@");
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}
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else
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{
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// This is a reloc to a section that cannot be folded.
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// Process it only in the first iteration.
|
|
if (!first_iteration)
|
|
continue;
|
|
|
|
uint64_t secn_flags = (it_v->first)->section_flags(it_v->second);
|
|
// This reloc points to a merge section. Hash the
|
|
// contents of this section.
|
|
if ((secn_flags & elfcpp::SHF_MERGE) != 0
|
|
&& parameters->target().can_icf_inline_merge_sections())
|
|
{
|
|
uint64_t entsize =
|
|
(it_v->first)->section_entsize(it_v->second);
|
|
long long offset = it_a->first;
|
|
|
|
// Handle SHT_RELA and SHT_REL addends. Only one of these
|
|
// addends exists. When pointing to a merge section, the
|
|
// addend only matters if it's relative to a section
|
|
// symbol. In order to unambiguously identify the target
|
|
// of the relocation, the compiler (and assembler) must use
|
|
// a local non-section symbol unless Symbol+Addend does in
|
|
// fact point directly to the target. (In other words,
|
|
// a bias for a pc-relative reference or a non-zero based
|
|
// access forces the use of a local symbol, and the addend
|
|
// is used only to provide that bias.)
|
|
uint64_t reloc_addend_value = 0;
|
|
if (is_section_symbol)
|
|
{
|
|
// Get the SHT_RELA addend. For RELA relocations,
|
|
// we have the addend from the relocation.
|
|
reloc_addend_value = it_a->second;
|
|
|
|
// Handle SHT_REL addends.
|
|
// For REL relocations, we need to fetch the addend
|
|
// from the section contents.
|
|
const unsigned char* reloc_addend_ptr =
|
|
contents + static_cast<unsigned long long>(*it_o);
|
|
|
|
// Update the addend value with the SHT_REL addend if
|
|
// available.
|
|
get_rel_addend(reloc_addend_ptr, *it_addend_size,
|
|
&reloc_addend_value);
|
|
|
|
// Ignore the addend when it is a negative value.
|
|
// See the comments in Merged_symbol_value::value
|
|
// in object.h.
|
|
if (reloc_addend_value < 0xffffff00)
|
|
offset = offset + reloc_addend_value;
|
|
}
|
|
|
|
section_size_type secn_len;
|
|
|
|
const unsigned char* str_contents =
|
|
(it_v->first)->section_contents(it_v->second,
|
|
&secn_len,
|
|
false) + offset;
|
|
gold_assert (offset < (long long) secn_len);
|
|
|
|
if ((secn_flags & elfcpp::SHF_STRINGS) != 0)
|
|
{
|
|
// String merge section.
|
|
const char* str_char =
|
|
reinterpret_cast<const char*>(str_contents);
|
|
switch(entsize)
|
|
{
|
|
case 1:
|
|
{
|
|
buffer.append(str_char);
|
|
break;
|
|
}
|
|
case 2:
|
|
{
|
|
const uint16_t* ptr_16 =
|
|
reinterpret_cast<const uint16_t*>(str_char);
|
|
unsigned int strlen_16 = 0;
|
|
// Find the NULL character.
|
|
while(*(ptr_16 + strlen_16) != 0)
|
|
strlen_16++;
|
|
buffer.append(str_char, strlen_16 * 2);
|
|
}
|
|
break;
|
|
case 4:
|
|
{
|
|
const uint32_t* ptr_32 =
|
|
reinterpret_cast<const uint32_t*>(str_char);
|
|
unsigned int strlen_32 = 0;
|
|
// Find the NULL character.
|
|
while(*(ptr_32 + strlen_32) != 0)
|
|
strlen_32++;
|
|
buffer.append(str_char, strlen_32 * 4);
|
|
}
|
|
break;
|
|
default:
|
|
gold_unreachable();
|
|
}
|
|
}
|
|
else
|
|
{
|
|
// Use the entsize to determine the length to copy.
|
|
uint64_t bufsize = entsize;
|
|
// If entsize is too big, copy all the remaining bytes.
|
|
if ((offset + entsize) > secn_len)
|
|
bufsize = secn_len - offset;
|
|
buffer.append(reinterpret_cast<const
|
|
char*>(str_contents),
|
|
bufsize);
|
|
}
|
|
buffer.append("@");
|
|
}
|
|
else if (gsym != NULL)
|
|
{
|
|
// If symbol name is available use that.
|
|
buffer.append(gsym->name());
|
|
// Append the addend.
|
|
buffer.append(addend_str);
|
|
buffer.append("@");
|
|
}
|
|
else
|
|
{
|
|
// Symbol name is not available, like for a local symbol,
|
|
// use object and section id.
|
|
buffer.append(it_v->first->name());
|
|
char secn_id[10];
|
|
snprintf(secn_id, sizeof(secn_id), "%u",it_v->second);
|
|
buffer.append(secn_id);
|
|
// Append the addend.
|
|
buffer.append(addend_str);
|
|
buffer.append("@");
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
if (first_iteration)
|
|
{
|
|
buffer.append("Contents = ");
|
|
|
|
const unsigned char* slice_end =
|
|
contents + std::min<section_offset_type>(plen, end_offset);
|
|
|
|
if (contents + start_offset < slice_end)
|
|
{
|
|
buffer.append(reinterpret_cast<const char*>(contents + start_offset),
|
|
slice_end - (contents + start_offset));
|
|
}
|
|
}
|
|
|
|
// Add any extra identity regions.
|
|
std::pair<Icf::Extra_identity_list::const_iterator,
|
|
Icf::Extra_identity_list::const_iterator>
|
|
extra_range = symtab->icf()->extra_identity_list().equal_range(secn);
|
|
for (Icf::Extra_identity_list::const_iterator it_ext = extra_range.first;
|
|
it_ext != extra_range.second; ++it_ext)
|
|
{
|
|
std::string external_fixed;
|
|
std::string external_all =
|
|
get_section_contents(first_iteration, &external_fixed,
|
|
it_ext->second.section, self_secn,
|
|
num_tracked_relocs, symtab,
|
|
kept_section_id, it_ext->second.offset,
|
|
it_ext->second.offset + it_ext->second.length);
|
|
buffer.append(external_fixed);
|
|
icf_reloc_buffer.append(external_all, external_fixed.length(),
|
|
std::string::npos);
|
|
}
|
|
|
|
if (first_iteration)
|
|
{
|
|
// Store the section contents that don't change to avoid recomputing
|
|
// during the next call to this function.
|
|
*fixed_cache = buffer;
|
|
}
|
|
else
|
|
{
|
|
gold_assert(buffer.empty());
|
|
|
|
// Reuse the contents computed in the previous iteration.
|
|
buffer.append(*fixed_cache);
|
|
}
|
|
|
|
buffer.append(icf_reloc_buffer);
|
|
return buffer;
|
|
}
|
|
|
|
// This function computes a checksum on each section to detect and form
|
|
// groups of identical sections. The first iteration does this for all
|
|
// sections.
|
|
// Further iterations do this only for the kept sections from each group to
|
|
// determine if larger groups of identical sections could be formed. The
|
|
// first section in each group is the kept section for that group.
|
|
//
|
|
// CRC32 is the checksumming algorithm and can have collisions. That is,
|
|
// two sections with different contents can have the same checksum. Hence,
|
|
// a multimap is used to maintain more than one group of checksum
|
|
// identical sections. A section is added to a group only after its
|
|
// contents are explicitly compared with the kept section of the group.
|
|
//
|
|
// Parameters :
|
|
// ITERATION_NUM : Invocation instance of this function.
|
|
// NUM_TRACKED_RELOCS : Vector reference to store the number of relocs
|
|
// to ICF sections.
|
|
// KEPT_SECTION_ID : Vector which maps folded sections to kept sections.
|
|
// ID_SECTION : Vector mapping a section to an unique integer.
|
|
// IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical
|
|
// sections is already known to be unique.
|
|
// SECTION_CONTENTS : Store the section's text and relocs to non-ICF
|
|
// sections.
|
|
|
|
static bool
|
|
match_sections(unsigned int iteration_num,
|
|
Symbol_table* symtab,
|
|
std::vector<unsigned int>* num_tracked_relocs,
|
|
std::vector<unsigned int>* kept_section_id,
|
|
const std::vector<Section_id>& id_section,
|
|
const std::vector<uint64_t>& section_addraligns,
|
|
std::vector<bool>* is_secn_or_group_unique,
|
|
std::vector<std::string>* section_contents)
|
|
{
|
|
Unordered_multimap<uint32_t, unsigned int> section_cksum;
|
|
std::pair<Unordered_multimap<uint32_t, unsigned int>::iterator,
|
|
Unordered_multimap<uint32_t, unsigned int>::iterator> key_range;
|
|
bool converged = true;
|
|
|
|
if (iteration_num == 1)
|
|
preprocess_for_unique_sections(id_section,
|
|
is_secn_or_group_unique,
|
|
NULL);
|
|
else
|
|
preprocess_for_unique_sections(id_section,
|
|
is_secn_or_group_unique,
|
|
section_contents);
|
|
|
|
std::vector<std::string> full_section_contents;
|
|
|
|
for (unsigned int i = 0; i < id_section.size(); i++)
|
|
{
|
|
full_section_contents.push_back("");
|
|
if ((*is_secn_or_group_unique)[i])
|
|
continue;
|
|
|
|
Section_id secn = id_section[i];
|
|
|
|
// Lock the object so we can read from it. This is only called
|
|
// single-threaded from queue_middle_tasks, so it is OK to lock.
|
|
// Unfortunately we have no way to pass in a Task token.
|
|
const Task* dummy_task = reinterpret_cast<const Task*>(-1);
|
|
Task_lock_obj<Object> tl(dummy_task, secn.first);
|
|
|
|
std::string this_secn_contents;
|
|
uint32_t cksum;
|
|
std::string* this_secn_cache = &((*section_contents)[i]);
|
|
if (iteration_num == 1)
|
|
{
|
|
unsigned int num_relocs = 0;
|
|
this_secn_contents = get_section_contents(true, this_secn_cache,
|
|
secn, secn, &num_relocs,
|
|
symtab, (*kept_section_id));
|
|
(*num_tracked_relocs)[i] = num_relocs;
|
|
}
|
|
else
|
|
{
|
|
if ((*kept_section_id)[i] != i)
|
|
{
|
|
// This section is already folded into something.
|
|
continue;
|
|
}
|
|
this_secn_contents = get_section_contents(false, this_secn_cache,
|
|
secn, secn, NULL,
|
|
symtab, (*kept_section_id));
|
|
}
|
|
|
|
const unsigned char* this_secn_contents_array =
|
|
reinterpret_cast<const unsigned char*>(this_secn_contents.c_str());
|
|
cksum = xcrc32(this_secn_contents_array, this_secn_contents.length(),
|
|
0xffffffff);
|
|
size_t count = section_cksum.count(cksum);
|
|
|
|
if (count == 0)
|
|
{
|
|
// Start a group with this cksum.
|
|
section_cksum.insert(std::make_pair(cksum, i));
|
|
full_section_contents[i] = this_secn_contents;
|
|
}
|
|
else
|
|
{
|
|
key_range = section_cksum.equal_range(cksum);
|
|
Unordered_multimap<uint32_t, unsigned int>::iterator it;
|
|
// Search all the groups with this cksum for a match.
|
|
for (it = key_range.first; it != key_range.second; ++it)
|
|
{
|
|
unsigned int kept_section = it->second;
|
|
if (full_section_contents[kept_section].length()
|
|
!= this_secn_contents.length())
|
|
continue;
|
|
if (memcmp(full_section_contents[kept_section].c_str(),
|
|
this_secn_contents.c_str(),
|
|
this_secn_contents.length()) != 0)
|
|
continue;
|
|
|
|
// Check section alignment here.
|
|
// The section with the larger alignment requirement
|
|
// should be kept. We assume alignment can only be
|
|
// zero or positive integral powers of two.
|
|
uint64_t align_i = section_addraligns[i];
|
|
uint64_t align_kept = section_addraligns[kept_section];
|
|
if (align_i <= align_kept)
|
|
{
|
|
(*kept_section_id)[i] = kept_section;
|
|
}
|
|
else
|
|
{
|
|
(*kept_section_id)[kept_section] = i;
|
|
it->second = i;
|
|
full_section_contents[kept_section].swap(
|
|
full_section_contents[i]);
|
|
}
|
|
|
|
converged = false;
|
|
break;
|
|
}
|
|
if (it == key_range.second)
|
|
{
|
|
// Create a new group for this cksum.
|
|
section_cksum.insert(std::make_pair(cksum, i));
|
|
full_section_contents[i] = this_secn_contents;
|
|
}
|
|
}
|
|
// If there are no relocs to foldable sections do not process
|
|
// this section any further.
|
|
if (iteration_num == 1 && (*num_tracked_relocs)[i] == 0)
|
|
(*is_secn_or_group_unique)[i] = true;
|
|
}
|
|
|
|
// If a section was folded into another section that was later folded
|
|
// again then the former has to be updated.
|
|
for (unsigned int i = 0; i < id_section.size(); i++)
|
|
{
|
|
// Find the end of the folding chain
|
|
unsigned int kept = i;
|
|
while ((*kept_section_id)[kept] != kept)
|
|
{
|
|
kept = (*kept_section_id)[kept];
|
|
}
|
|
// Update every element of the chain
|
|
unsigned int current = i;
|
|
while ((*kept_section_id)[current] != kept)
|
|
{
|
|
unsigned int next = (*kept_section_id)[current];
|
|
(*kept_section_id)[current] = kept;
|
|
current = next;
|
|
}
|
|
}
|
|
|
|
return converged;
|
|
}
|
|
|
|
// During safe icf (--icf=safe), only fold functions that are ctors or dtors.
|
|
// This function returns true if the section name is that of a ctor or a dtor.
|
|
|
|
static bool
|
|
is_function_ctor_or_dtor(const std::string& section_name)
|
|
{
|
|
const char* mangled_func_name = strrchr(section_name.c_str(), '.');
|
|
gold_assert(mangled_func_name != NULL);
|
|
if ((is_prefix_of("._ZN", mangled_func_name)
|
|
|| is_prefix_of("._ZZ", mangled_func_name))
|
|
&& (is_gnu_v3_mangled_ctor(mangled_func_name + 1)
|
|
|| is_gnu_v3_mangled_dtor(mangled_func_name + 1)))
|
|
{
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// Iterate through the .eh_frame section that has index
|
|
// `ehframe_shndx` in `object`, adding entries to extra_identity_list_
|
|
// that will cause the contents of each FDE and its CIE to be included
|
|
// in the logical ICF identity of the function that the FDE refers to.
|
|
|
|
bool
|
|
Icf::add_ehframe_links(Relobj* object, unsigned int ehframe_shndx,
|
|
Reloc_info& relocs)
|
|
{
|
|
section_size_type contents_len;
|
|
const unsigned char* pcontents = object->section_contents(ehframe_shndx,
|
|
&contents_len,
|
|
false);
|
|
const unsigned char* p = pcontents;
|
|
const unsigned char* pend = pcontents + contents_len;
|
|
|
|
Sections_reachable_info::iterator it_target = relocs.section_info.begin();
|
|
Sections_reachable_info::iterator it_target_end = relocs.section_info.end();
|
|
Offset_info::iterator it_offset = relocs.offset_info.begin();
|
|
Offset_info::iterator it_offset_end = relocs.offset_info.end();
|
|
|
|
// Maps section offset to the length of the CIE defined at that offset.
|
|
typedef Unordered_map<section_offset_type, section_size_type> Cie_map;
|
|
Cie_map cies;
|
|
|
|
uint32_t (*read_swap_32)(const unsigned char*);
|
|
if (object->is_big_endian())
|
|
read_swap_32 = &elfcpp::Swap<32, true>::readval;
|
|
else
|
|
read_swap_32 = &elfcpp::Swap<32, false>::readval;
|
|
|
|
// TODO: The logic for parsing the CIE/FDE framing is copied from
|
|
// Eh_frame::do_add_ehframe_input_section() and might want to be
|
|
// factored into a shared helper function.
|
|
while (p < pend)
|
|
{
|
|
if (pend - p < 4)
|
|
return false;
|
|
|
|
unsigned int len = read_swap_32(p);
|
|
p += 4;
|
|
if (len == 0)
|
|
{
|
|
// We should only find a zero-length entry at the end of the
|
|
// section.
|
|
if (p < pend)
|
|
return false;
|
|
break;
|
|
}
|
|
// We don't support a 64-bit .eh_frame.
|
|
if (len == 0xffffffff)
|
|
return false;
|
|
if (static_cast<unsigned int>(pend - p) < len)
|
|
return false;
|
|
|
|
const unsigned char* const pentend = p + len;
|
|
|
|
if (pend - p < 4)
|
|
return false;
|
|
|
|
unsigned int id = read_swap_32(p);
|
|
p += 4;
|
|
|
|
if (id == 0)
|
|
{
|
|
// CIE.
|
|
cies.insert(std::make_pair(p - pcontents, len - 4));
|
|
}
|
|
else
|
|
{
|
|
// FDE.
|
|
Cie_map::const_iterator it;
|
|
it = cies.find((p - pcontents) - (id - 4));
|
|
if (it == cies.end())
|
|
return false;
|
|
|
|
// Figure out which section this FDE refers into. The word at `p`
|
|
// is an address, and we expect to see a relocation there. If not,
|
|
// this FDE isn't ICF-relevant.
|
|
while (it_offset != it_offset_end
|
|
&& it_target != it_target_end
|
|
&& static_cast<ptrdiff_t>(*it_offset) < (p - pcontents))
|
|
{
|
|
++it_offset;
|
|
++it_target;
|
|
}
|
|
if (it_offset != it_offset_end
|
|
&& it_target != it_target_end
|
|
&& static_cast<ptrdiff_t>(*it_offset) == (p - pcontents))
|
|
{
|
|
// Found a reloc. Add this FDE and its CIE as extra identity
|
|
// info for the section it refers to.
|
|
Extra_identity_info rec_fde = {Section_id(object, ehframe_shndx),
|
|
p - pcontents, len - 4};
|
|
Extra_identity_info rec_cie = {Section_id(object, ehframe_shndx),
|
|
it->first, it->second};
|
|
extra_identity_list_.insert(std::make_pair(*it_target, rec_fde));
|
|
extra_identity_list_.insert(std::make_pair(*it_target, rec_cie));
|
|
}
|
|
}
|
|
|
|
p = pentend;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
// This is the main ICF function called in gold.cc. This does the
|
|
// initialization and calls match_sections repeatedly (thrice by default)
|
|
// which computes the crc checksums and detects identical functions.
|
|
|
|
void
|
|
Icf::find_identical_sections(const Input_objects* input_objects,
|
|
Symbol_table* symtab)
|
|
{
|
|
unsigned int section_num = 0;
|
|
std::vector<unsigned int> num_tracked_relocs;
|
|
std::vector<uint64_t> section_addraligns;
|
|
std::vector<bool> is_secn_or_group_unique;
|
|
std::vector<std::string> section_contents;
|
|
const Target& target = parameters->target();
|
|
|
|
// Decide which sections are possible candidates first.
|
|
|
|
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
|
|
p != input_objects->relobj_end();
|
|
++p)
|
|
{
|
|
// Lock the object so we can read from it. This is only called
|
|
// single-threaded from queue_middle_tasks, so it is OK to lock.
|
|
// Unfortunately we have no way to pass in a Task token.
|
|
const Task* dummy_task = reinterpret_cast<const Task*>(-1);
|
|
Task_lock_obj<Object> tl(dummy_task, *p);
|
|
std::vector<unsigned int> eh_frame_ind;
|
|
|
|
for (unsigned int i = 0; i < (*p)->shnum(); ++i)
|
|
{
|
|
if ((*p)->section_size(i) == 0)
|
|
continue;
|
|
const std::string section_name = (*p)->section_name(i);
|
|
if (!is_section_foldable_candidate(section_name))
|
|
{
|
|
if (is_prefix_of(".eh_frame", section_name.c_str()))
|
|
eh_frame_ind.push_back(i);
|
|
continue;
|
|
}
|
|
|
|
if (!(*p)->is_section_included(i))
|
|
continue;
|
|
if (parameters->options().gc_sections()
|
|
&& symtab->gc()->is_section_garbage(*p, i))
|
|
continue;
|
|
// With --icf=safe, check if the mangled function name is a ctor
|
|
// or a dtor. The mangled function name can be obtained from the
|
|
// section name by stripping the section prefix.
|
|
if (parameters->options().icf_safe_folding()
|
|
&& !is_function_ctor_or_dtor(section_name)
|
|
&& (!target.can_check_for_function_pointers()
|
|
|| section_has_function_pointers(*p, i)))
|
|
{
|
|
continue;
|
|
}
|
|
this->id_section_.push_back(Section_id(*p, i));
|
|
this->section_id_[Section_id(*p, i)] = section_num;
|
|
this->kept_section_id_.push_back(section_num);
|
|
num_tracked_relocs.push_back(0);
|
|
section_addraligns.push_back((*p)->section_addralign(i));
|
|
is_secn_or_group_unique.push_back(false);
|
|
section_contents.push_back("");
|
|
section_num++;
|
|
}
|
|
|
|
for (std::vector<unsigned int>::iterator it_eh_ind = eh_frame_ind.begin();
|
|
it_eh_ind != eh_frame_ind.end(); ++it_eh_ind)
|
|
{
|
|
// gc_process_relocs() recorded relocations for this
|
|
// section even though we can't fold it. We need to
|
|
// use those relocations to associate other foldable
|
|
// sections with the FDEs and CIEs that are relevant
|
|
// to them, so we can avoid merging sections that
|
|
// don't have identical exception-handling behavior.
|
|
|
|
Section_id sect(*p, *it_eh_ind);
|
|
Reloc_info_list::iterator it_rel = this->reloc_info_list().find(sect);
|
|
if (it_rel != this->reloc_info_list().end())
|
|
{
|
|
if (!add_ehframe_links(*p, *it_eh_ind, it_rel->second))
|
|
{
|
|
gold_warning(_("could not parse eh_frame section %s(%s); ICF "
|
|
"might not preserve exception handling "
|
|
"behavior"),
|
|
(*p)->name().c_str(),
|
|
(*p)->section_name(*it_eh_ind).c_str());
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
unsigned int num_iterations = 0;
|
|
|
|
// Default number of iterations to run ICF is 3.
|
|
unsigned int max_iterations = (parameters->options().icf_iterations() > 0)
|
|
? parameters->options().icf_iterations()
|
|
: 3;
|
|
|
|
bool converged = false;
|
|
|
|
while (!converged && (num_iterations < max_iterations))
|
|
{
|
|
num_iterations++;
|
|
converged = match_sections(num_iterations, symtab,
|
|
&num_tracked_relocs, &this->kept_section_id_,
|
|
this->id_section_, section_addraligns,
|
|
&is_secn_or_group_unique, §ion_contents);
|
|
}
|
|
|
|
if (parameters->options().print_icf_sections())
|
|
{
|
|
if (converged)
|
|
gold_info(_("%s: ICF Converged after %u iteration(s)"),
|
|
program_name, num_iterations);
|
|
else
|
|
gold_info(_("%s: ICF stopped after %u iteration(s)"),
|
|
program_name, num_iterations);
|
|
}
|
|
|
|
// Unfold --keep-unique symbols.
|
|
for (options::String_set::const_iterator p =
|
|
parameters->options().keep_unique_begin();
|
|
p != parameters->options().keep_unique_end();
|
|
++p)
|
|
{
|
|
const char* name = p->c_str();
|
|
Symbol* sym = symtab->lookup(name);
|
|
if (sym == NULL)
|
|
{
|
|
gold_warning(_("Could not find symbol %s to unfold\n"), name);
|
|
}
|
|
else if (sym->source() == Symbol::FROM_OBJECT
|
|
&& !sym->object()->is_dynamic())
|
|
{
|
|
Relobj* obj = static_cast<Relobj*>(sym->object());
|
|
bool is_ordinary;
|
|
unsigned int shndx = sym->shndx(&is_ordinary);
|
|
if (is_ordinary)
|
|
{
|
|
this->unfold_section(obj, shndx);
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
this->icf_ready();
|
|
}
|
|
|
|
// Unfolds the section denoted by OBJ and SHNDX if folded.
|
|
|
|
void
|
|
Icf::unfold_section(Relobj* obj, unsigned int shndx)
|
|
{
|
|
Section_id secn(obj, shndx);
|
|
Uniq_secn_id_map::iterator it = this->section_id_.find(secn);
|
|
if (it == this->section_id_.end())
|
|
return;
|
|
unsigned int section_num = it->second;
|
|
unsigned int kept_section_id = this->kept_section_id_[section_num];
|
|
if (kept_section_id != section_num)
|
|
this->kept_section_id_[section_num] = section_num;
|
|
}
|
|
|
|
// This function determines if the section corresponding to the
|
|
// given object and index is folded based on if the kept section
|
|
// is different from this section.
|
|
|
|
bool
|
|
Icf::is_section_folded(Relobj* obj, unsigned int shndx)
|
|
{
|
|
Section_id secn(obj, shndx);
|
|
Uniq_secn_id_map::iterator it = this->section_id_.find(secn);
|
|
if (it == this->section_id_.end())
|
|
return false;
|
|
unsigned int section_num = it->second;
|
|
unsigned int kept_section_id = this->kept_section_id_[section_num];
|
|
return kept_section_id != section_num;
|
|
}
|
|
|
|
// This function returns the folded section for the given section.
|
|
|
|
Section_id
|
|
Icf::get_folded_section(Relobj* dup_obj, unsigned int dup_shndx)
|
|
{
|
|
Section_id dup_secn(dup_obj, dup_shndx);
|
|
Uniq_secn_id_map::iterator it = this->section_id_.find(dup_secn);
|
|
gold_assert(it != this->section_id_.end());
|
|
unsigned int section_num = it->second;
|
|
unsigned int kept_section_id = this->kept_section_id_[section_num];
|
|
Section_id folded_section = this->id_section_[kept_section_id];
|
|
return folded_section;
|
|
}
|
|
|
|
} // End of namespace gold.
|