path: root/gas/doc/c-aarch64.texi

@c Copyright 2009, 2010, 2011, 2012  Free Software Foundation, Inc.
@c Contributed by ARM Ltd.
@c This is part of the GAS manual.
@c For copying conditions, see the file as.texinfo.
@c man end

@ifset GENERIC
@page
@node AArch64-Dependent
@chapter AArch64 Dependent Features
@end ifset

@ifclear GENERIC
@node Machine Dependencies
@chapter AArch64 Dependent Features
@end ifclear

@cindex AArch64 support
@cindex Thumb support
@menu
* AArch64 Options::              Options
* AArch64 Syntax::               Syntax
* AArch64 Floating Point::       Floating Point
* AArch64 Directives::           AArch64 Machine Directives
* AArch64 Opcodes::              Opcodes
* AArch64 Mapping Symbols::      Mapping Symbols
@end menu

@node AArch64 Options
@section Options
@cindex AArch64 options (none)
@cindex options for AArch64 (none)

@c man begin OPTIONS
@table @gcctabopt

@cindex @code{-EB} command line option, AArch64
@item -EB
This option specifies that the output generated by the assembler should
be marked as being encoded for a big-endian processor.

@cindex @code{-EL} command line option, AArch64
@item -EL
This option specifies that the output generated by the assembler should
be marked as being encoded for a little-endian processor.

@end table
@c man end

@node AArch64 Syntax
@section Syntax
@menu
* AArch64-Chars::                Special Characters
* AArch64-Regs::                 Register Names
* AArch64-Relocations::	     Relocations
@end menu

@node AArch64-Chars
@subsection Special Characters

@cindex line comment character, AArch64
@cindex AArch64 line comment character
The presence of a @samp{//} on a line indicates the start of a comment
that extends to the end of the current line.  If a @samp{#} appears as
the first character of a line, the whole line is treated as a comment.

@cindex line separator, AArch64
@cindex statement separator, AArch64
@cindex AArch64 line separator
The @samp{;} character can be used instead of a newline to separate
statements.

@cindex immediate character, AArch64
@cindex AArch64 immediate character
The @samp{#} can be optionally used to indicate immediate operands.

@node AArch64-Regs
@subsection Register Names

@cindex AArch64 register names
@cindex register names, AArch64
Please refer to the section @samp{4.4 Register Names} of
@samp{ARMv8 Instruction Set Overview}, which is available at
@uref{http://infocenter.arm.com}.

@node AArch64-Relocations
@subsection Relocations

@cindex relocations, AArch64
@cindex AArch64 relocations
@cindex MOVN, MOVZ and MOVK group relocations, AArch64
Relocations for @samp{MOVZ} and @samp{MOVK} instructions can be generated
by prefixing the label with @samp{#:abs_g2:} etc.
For example to load the 48-bit absolute address of @var{foo} into x0:

@smallexample
        movz x0, #:abs_g2:foo		// bits 32-47, overflow check
        movk x0, #:abs_g1_nc:foo	// bits 16-31, no overflow check
        movk x0, #:abs_g0_nc:foo	// bits  0-15, no overflow check
@end smallexample

@cindex ADRP, ADD, LDR/STR group relocations, AArch64
Relocations for @samp{ADRP}, and @samp{ADD}, @samp{LDR} or @samp{STR}
instructions can be generated by prefixing the label with
@samp{#:pg_hi21:} and @samp{#:lo12:} respectively.

For example to use 33-bit (+/-4GB) pc-relative addressing to 
load the address of @var{foo} into x0:

@smallexample
        adrp x0, #:pg_hi21:foo
        add  x0, x0, #:lo12:foo
@end smallexample

Or to load the value of @var{foo} into x0:

@smallexample
        adrp x0, #:pg_hi21:foo
        ldr  x0, [x0, #:lo12:foo]
@end smallexample

Note that @samp{#:pg_hi21:} is optional.

@smallexample
        adrp x0, foo
@end smallexample

is equivalent to

@smallexample
        adrp x0, #:pg_hi21:foo
@end smallexample

@node AArch64 Floating Point
@section Floating Point

@cindex floating point, AArch64 (@sc{ieee})
@cindex AArch64 floating point (@sc{ieee})
The AArch64 architecture uses @sc{ieee} floating-point numbers.

@node AArch64 Directives
@section AArch64 Machine Directives

@cindex machine directives, AArch64
@cindex AArch64 machine directives
@table @code

@c AAAAAAAAAAAAAAAAAAAAAAAAA
@c BBBBBBBBBBBBBBBBBBBBBBBBBB

@cindex @code{.bss} directive, AArch64
@item .bss
This directive switches to the @code{.bss} section.

@c CCCCCCCCCCCCCCCCCCCCCCCCCC
@c DDDDDDDDDDDDDDDDDDDDDDDDDD
@c EEEEEEEEEEEEEEEEEEEEEEEEEE
@c FFFFFFFFFFFFFFFFFFFFFFFFFF
@c GGGGGGGGGGGGGGGGGGGGGGGGGG
@c HHHHHHHHHHHHHHHHHHHHHHHHHH
@c IIIIIIIIIIIIIIIIIIIIIIIIII
@c JJJJJJJJJJJJJJJJJJJJJJJJJJ
@c KKKKKKKKKKKKKKKKKKKKKKKKKK
@c LLLLLLLLLLLLLLLLLLLLLLLLLL

@cindex @code{.ltorg} directive, AArch64
@item .ltorg
This directive causes the current contents of the literal pool to be
dumped into the current section (which is assumed to be the .text
section) at the current location (aligned to a word boundary).
@code{GAS} maintains a separate literal pool for each section and each
sub-section.  The @code{.ltorg} directive will only affect the literal
pool of the current section and sub-section.  At the end of assembly
all remaining, un-empty literal pools will automatically be dumped.

Note - older versions of @code{GAS} would dump the current literal
pool any time a section change occurred.  This is no longer done, since
it prevents accurate control of the placement of literal pools.

@c MMMMMMMMMMMMMMMMMMMMMMMMMM

@c NNNNNNNNNNNNNNNNNNNNNNNNNN
@c OOOOOOOOOOOOOOOOOOOOOOOOOO

@c PPPPPPPPPPPPPPPPPPPPPPPPPP

@cindex @code{.pool} directive, AArch64
@item .pool
This is a synonym for .ltorg.

@c QQQQQQQQQQQQQQQQQQQQQQQQQQ
@c RRRRRRRRRRRRRRRRRRRRRRRRRR

@cindex @code{.req} directive, AArch64
@item @var{name} .req @var{register name}
This creates an alias for @var{register name} called @var{name}.  For
example:

@smallexample
        foo .req w0
@end smallexample

@c SSSSSSSSSSSSSSSSSSSSSSSSSS

@c TTTTTTTTTTTTTTTTTTTTTTTTTT

@c UUUUUUUUUUUUUUUUUUUUUUUUUU

@cindex @code{.unreq} directive, AArch64
@item .unreq @var{alias-name}
This undefines a register alias which was previously defined using the
@code{req} directive.  For example:

@smallexample
        foo .req w0
        .unreq foo
@end smallexample

An error occurs if the name is undefined.  Note - this pseudo op can
be used to delete builtin in register name aliases (eg 'w0').  This
should only be done if it is really necessary.

@c VVVVVVVVVVVVVVVVVVVVVVVVVV

@c WWWWWWWWWWWWWWWWWWWWWWWWWW
@c XXXXXXXXXXXXXXXXXXXXXXXXXX
@c YYYYYYYYYYYYYYYYYYYYYYYYYY
@c ZZZZZZZZZZZZZZZZZZZZZZZZZZ

@end table

@node AArch64 Opcodes
@section Opcodes

@cindex AArch64 opcodes
@cindex opcodes for AArch64
@code{@value{AS}} implements all the standard AArch64 opcodes.  It also
implements several pseudo opcodes, including several synthetic load
instructions. 

@table @code

@cindex @code{LDR reg,=<expr>} pseudo op, AArch64
@item LDR =
@smallexample
  ldr <register> , =<expression>
@end smallexample

The constant expression will be placed into the nearest literal pool (if it not
already there) and a PC-relative LDR instruction will be generated.

@end table

For more information on the AArch64 instruction set and assembly language
notation, see @samp{ARMv8 Instruction Set Overview} available at
@uref{http://infocenter.arm.com}.


@node AArch64 Mapping Symbols
@section Mapping Symbols

The AArch64 ELF specification requires that special symbols be inserted
into object files to mark certain features:

@table @code

@cindex @code{$x}
@item $x
At the start of a region of code containing AArch64 instructions.

@cindex @code{$d}
@item $d
At the start of a region of data.

@end table