Projet_SETI_RISC-V/riscv-gnu-toolchain/gdb/gas/doc/c-nios2.texi

@c Copyright (C) 2012-2022 Free Software Foundation, Inc.
@c This is part of the GAS manual.
@c For copying conditions, see the file as.texinfo.
@c man end
@ifset GENERIC
@page
@node NiosII-Dependent
@chapter Nios II Dependent Features
@end ifset
@ifclear GENERIC
@node Machine Dependencies
@chapter Nios II Dependent Features
@end ifclear

@cindex Altera Nios II support
@cindex Nios support
@cindex Nios II support
@menu
* Nios II Options::              Options
* Nios II Syntax::               Syntax
* Nios II Relocations::          Relocations
* Nios II Directives::           Nios II Machine Directives
* Nios II Opcodes::              Opcodes
@end menu

@node Nios II Options
@section Options
@cindex Nios II options
@cindex options for Nios II

@c man begin OPTIONS
@table @gcctabopt

@cindex @code{relax-section} command-line option, Nios II
@item -relax-section
Replace identified out-of-range branches with PC-relative @code{jmp}
sequences when possible.  The generated code sequences are suitable
for use in position-independent code, but there is a practical limit
on the extended branch range because of the length of the sequences.
This option is the default.

@cindex @code{relax-all} command-line option, Nios II
@item -relax-all
Replace branch instructions not determinable to be in range
and all call instructions with @code{jmp} and @code{callr} sequences
(respectively).  This option generates absolute relocations against the
target symbols and is not appropriate for position-independent code.

@cindex @code{no-relax} command-line option, Nios II
@item -no-relax
Do not replace any branches or calls.

@cindex @code{EB} command-line option, Nios II
@item -EB
Generate big-endian output.

@cindex @code{EL} command-line option, Nios II
@item -EL
Generate little-endian output.  This is the default.

@cindex @code{march} command-line option, Nios II
@item -march=@var{architecture}
This option specifies the target architecture.  The assembler issues
an error message if an attempt is made to assemble an instruction which
will not execute on the target architecture.  The following architecture
names are recognized:
@code{r1},
@code{r2}.  
The default is @code{r1}.

@end table
@c man end

@node Nios II Syntax
@section Syntax
@menu
* Nios II Chars::                Special Characters
@end menu


@node Nios II Chars
@subsection Special Characters

@cindex line comment character, Nios II
@cindex Nios II line comment character
@cindex line separator character, Nios II
@cindex Nios II line separator character
@samp{#} is the line comment character.
@samp{;} is the line separator character.


@node Nios II Relocations
@section Nios II Machine Relocations

@cindex machine relocations, Nios II
@cindex Nios II machine relocations

@table @code
@cindex @code{hiadj} directive, Nios II
@item %hiadj(@var{expression})
Extract the upper 16 bits of @var{expression} and add 
one if the 15th bit is set. 

The value of @code{%hiadj(@var{expression})} is:
@smallexample
((@var{expression} >> 16) & 0xffff) + ((@var{expression} >> 15) & 0x01)
@end smallexample

The @code{%hiadj} relocation is intended to be used with
the @code{addi}, @code{ld} or @code{st} instructions
along with a @code{%lo}, in order to load a 32-bit constant.

@smallexample
movhi r2, %hiadj(symbol)
addi r2, r2, %lo(symbol)
@end smallexample

@cindex @code{hi} directive, Nios II
@item %hi(@var{expression})
Extract the upper 16 bits of @var{expression}.

@cindex @code{lo} directive, Nios II
@item %lo(@var{expression})
Extract the lower 16 bits of @var{expression}.

@cindex @code{gprel} directive, Nios II
@item %gprel(@var{expression})
Subtract the value of the symbol @code{_gp} from
@var{expression}. 

The intention of the @code{%gprel} relocation is
to have a fast small area of memory which only
takes a 16-bit immediate to access.

@smallexample
	.section .sdata
fastint:
	.int 123
	.section .text
	ldw r4, %gprel(fastint)(gp)
@end smallexample

@cindex @code{call} directive, Nios II
@cindex @code{call_lo} directive, Nios II
@cindex @code{call_hiadj} directive, Nios II
@cindex @code{got} directive, Nios II
@cindex @code{got_lo} directive, Nios II
@cindex @code{got_hiadj} directive, Nios II
@cindex @code{gotoff} directive, Nios II
@cindex @code{gotoff_lo} directive, Nios II
@cindex @code{gotoff_hiadj} directive, Nios II
@cindex @code{tls_gd} directive, Nios II
@cindex @code{tls_ie} directive, Nios II
@cindex @code{tls_le} directive, Nios II
@cindex @code{tls_ldm} directive, Nios II
@cindex @code{tls_ldo} directive, Nios II
@item %call(@var{expression})
@item %call_lo(@var{expression})
@item %call_hiadj(@var{expression})
@itemx %got(@var{expression})
@itemx %got_lo(@var{expression})
@itemx %got_hiadj(@var{expression})
@itemx %gotoff(@var{expression})
@itemx %gotoff_lo(@var{expression})
@itemx %gotoff_hiadj(@var{expression})
@itemx %tls_gd(@var{expression})
@itemx %tls_ie(@var{expression})
@itemx %tls_le(@var{expression})
@itemx %tls_ldm(@var{expression})
@itemx %tls_ldo(@var{expression})

These relocations support the ABI for Linux Systems documented in the
@cite{Nios II Processor Reference Handbook}.
@end table


@node Nios II Directives
@section Nios II Machine Directives

@cindex machine directives, Nios II
@cindex Nios II machine directives

@table @code

@cindex @code{align} directive, Nios II
@item .align @var{expression} [, @var{expression}]
This is the generic @code{.align} directive, however
this aligns to a power of two.

@cindex @code{half} directive, Nios II
@item .half @var{expression}
Create an aligned constant 2 bytes in size.

@cindex @code{word} directive, Nios II
@item .word @var{expression}
Create an aligned constant 4 bytes in size.

@cindex @code{dword} directive, Nios II
@item .dword @var{expression}
Create an aligned constant 8 bytes in size.

@cindex @code{2byte} directive, Nios II
@item .2byte @var{expression}
Create an unaligned constant 2 bytes in size.

@cindex @code{4byte} directive, Nios II
@item .4byte @var{expression}
Create an unaligned constant 4 bytes in size.

@cindex @code{8byte} directive, Nios II
@item .8byte @var{expression}
Create an unaligned constant 8 bytes in size.

@cindex @code{16byte} directive, Nios II
@item .16byte @var{expression}
Create an unaligned constant 16 bytes in size.

@cindex @code{set noat} directive, Nios II
@item .set noat
Allows assembly code to use @code{at} register without 
warning.  Macro or relaxation expansions
generate warnings.

@cindex @code{set at} directive, Nios II
@item .set at
Assembly code using @code{at} register generates
warnings, and macro expansion and relaxation are
enabled.

@cindex @code{set nobreak} directive, Nios II
@item .set nobreak
Allows assembly code to use @code{ba} and @code{bt}
registers without warning. 

@cindex @code{set break} directive, Nios II
@item .set break
Turns warnings back on for using @code{ba} and @code{bt}
registers.

@cindex @code{set norelax} directive, Nios II
@item .set norelax
Do not replace any branches or calls.

@cindex @code{set relaxsection} directive, Nios II
@item .set relaxsection
Replace identified out-of-range branches with 
@code{jmp} sequences (default).

@cindex @code{set relaxall} directive, Nios II
@item .set relaxsection
Replace all branch and call instructions with
@code{jmp} and @code{callr} sequences.

@cindex @code{set} directive, Nios II
@item .set @dots{}
All other @code{.set} are the normal use.

@end table

@node Nios II Opcodes
@section Opcodes

@cindex Nios II opcodes
@cindex opcodes for Nios II
@code{@value{AS}} implements all the standard Nios II opcodes documented in the
@cite{Nios II Processor Reference Handbook}, including the assembler
pseudo-instructions.