97d40d3d4a
us up to version 2.17.50.20070703, at the last GPLv2 commit. Amongst others, this added upstream support for some FreeBSD-specific things that we previously had to manually hack in, such as the OSABI label support, and so on. There are also quite a number of new files, some for cpu's (e.g. SPU) that we may or may not be interested in, but those can be cleaned up later on, if needed.
736 lines
22 KiB
Plaintext
736 lines
22 KiB
Plaintext
@c Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
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@c Free Software Foundation, Inc.
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@c This is part of the GAS manual.
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@c For copying conditions, see the file as.texinfo.
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@ifset GENERIC
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@page
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@node ARM-Dependent
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@chapter ARM Dependent Features
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@end ifset
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@ifclear GENERIC
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@node Machine Dependencies
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@chapter ARM Dependent Features
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@end ifclear
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@cindex ARM support
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@cindex Thumb support
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@menu
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* ARM Options:: Options
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* ARM Syntax:: Syntax
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* ARM Floating Point:: Floating Point
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* ARM Directives:: ARM Machine Directives
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* ARM Opcodes:: Opcodes
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* ARM Mapping Symbols:: Mapping Symbols
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@end menu
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@node ARM Options
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@section Options
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@cindex ARM options (none)
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@cindex options for ARM (none)
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@table @code
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@cindex @code{-mcpu=} command line option, ARM
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@item -mcpu=@var{processor}[+@var{extension}@dots{}]
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This option specifies the target processor. The assembler will issue an
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error message if an attempt is made to assemble an instruction which
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will not execute on the target processor. The following processor names are
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recognized:
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@code{arm1},
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@code{arm2},
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@code{arm250},
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@code{arm3},
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@code{arm6},
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@code{arm60},
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@code{arm600},
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@code{arm610},
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@code{arm620},
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@code{arm7},
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@code{arm7m},
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@code{arm7d},
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@code{arm7dm},
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@code{arm7di},
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@code{arm7dmi},
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@code{arm70},
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@code{arm700},
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@code{arm700i},
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@code{arm710},
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@code{arm710t},
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@code{arm720},
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@code{arm720t},
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@code{arm740t},
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@code{arm710c},
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@code{arm7100},
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@code{arm7500},
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@code{arm7500fe},
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@code{arm7t},
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@code{arm7tdmi},
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@code{arm7tdmi-s},
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@code{arm8},
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@code{arm810},
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@code{strongarm},
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@code{strongarm1},
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@code{strongarm110},
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@code{strongarm1100},
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@code{strongarm1110},
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@code{arm9},
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@code{arm920},
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@code{arm920t},
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@code{arm922t},
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@code{arm940t},
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@code{arm9tdmi},
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@code{arm9e},
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@code{arm926e},
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@code{arm926ej-s},
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@code{arm946e-r0},
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@code{arm946e},
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@code{arm946e-s},
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@code{arm966e-r0},
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@code{arm966e},
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@code{arm966e-s},
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@code{arm968e-s},
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@code{arm10t},
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@code{arm10tdmi},
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@code{arm10e},
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@code{arm1020},
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@code{arm1020t},
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@code{arm1020e},
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@code{arm1022e},
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@code{arm1026ej-s},
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@code{arm1136j-s},
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@code{arm1136jf-s},
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@code{arm1156t2-s},
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@code{arm1156t2f-s},
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@code{arm1176jz-s},
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@code{arm1176jzf-s},
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@code{mpcore},
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@code{mpcorenovfp},
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@code{cortex-a8},
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@code{cortex-r4},
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@code{cortex-m3},
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@code{ep9312} (ARM920 with Cirrus Maverick coprocessor),
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@code{i80200} (Intel XScale processor)
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@code{iwmmxt} (Intel(r) XScale processor with Wireless MMX(tm) technology coprocessor)
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and
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@code{xscale}.
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The special name @code{all} may be used to allow the
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assembler to accept instructions valid for any ARM processor.
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In addition to the basic instruction set, the assembler can be told to
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accept various extension mnemonics that extend the processor using the
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co-processor instruction space. For example, @code{-mcpu=arm920+maverick}
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is equivalent to specifying @code{-mcpu=ep9312}. The following extensions
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are currently supported:
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@code{+maverick}
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@code{+iwmmxt}
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and
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@code{+xscale}.
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@cindex @code{-march=} command line option, ARM
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@item -march=@var{architecture}[+@var{extension}@dots{}]
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This option specifies the target architecture. The assembler will issue
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an error message if an attempt is made to assemble an instruction which
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will not execute on the target architecture. The following architecture
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names are recognized:
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@code{armv1},
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@code{armv2},
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@code{armv2a},
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@code{armv2s},
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@code{armv3},
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@code{armv3m},
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@code{armv4},
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@code{armv4xm},
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@code{armv4t},
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@code{armv4txm},
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@code{armv5},
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@code{armv5t},
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@code{armv5txm},
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@code{armv5te},
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@code{armv5texp},
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@code{armv6},
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@code{armv6j},
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@code{armv6k},
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@code{armv6z},
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@code{armv6zk},
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@code{armv7},
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@code{armv7-a},
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@code{armv7-r},
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@code{armv7-m},
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@code{iwmmxt}
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and
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@code{xscale}.
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If both @code{-mcpu} and
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@code{-march} are specified, the assembler will use
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the setting for @code{-mcpu}.
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The architecture option can be extended with the same instruction set
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extension options as the @code{-mcpu} option.
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@cindex @code{-mfpu=} command line option, ARM
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@item -mfpu=@var{floating-point-format}
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This option specifies the floating point format to assemble for. The
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assembler will issue an error message if an attempt is made to assemble
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an instruction which will not execute on the target floating point unit.
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The following format options are recognized:
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@code{softfpa},
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@code{fpe},
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@code{fpe2},
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@code{fpe3},
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@code{fpa},
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@code{fpa10},
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@code{fpa11},
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@code{arm7500fe},
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@code{softvfp},
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@code{softvfp+vfp},
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@code{vfp},
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@code{vfp10},
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@code{vfp10-r0},
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@code{vfp9},
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@code{vfpxd},
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@code{arm1020t},
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@code{arm1020e},
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@code{arm1136jf-s}
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and
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@code{maverick}.
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In addition to determining which instructions are assembled, this option
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also affects the way in which the @code{.double} assembler directive behaves
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when assembling little-endian code.
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The default is dependent on the processor selected. For Architecture 5 or
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later, the default is to assembler for VFP instructions; for earlier
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architectures the default is to assemble for FPA instructions.
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@cindex @code{-mthumb} command line option, ARM
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@item -mthumb
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This option specifies that the assembler should start assembling Thumb
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instructions; that is, it should behave as though the file starts with a
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@code{.code 16} directive.
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@cindex @code{-mthumb-interwork} command line option, ARM
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@item -mthumb-interwork
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This option specifies that the output generated by the assembler should
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be marked as supporting interworking.
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@cindex @code{-mapcs} command line option, ARM
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@item -mapcs @code{[26|32]}
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This option specifies that the output generated by the assembler should
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be marked as supporting the indicated version of the Arm Procedure.
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Calling Standard.
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@cindex @code{-matpcs} command line option, ARM
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@item -matpcs
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This option specifies that the output generated by the assembler should
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be marked as supporting the Arm/Thumb Procedure Calling Standard. If
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enabled this option will cause the assembler to create an empty
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debugging section in the object file called .arm.atpcs. Debuggers can
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use this to determine the ABI being used by.
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@cindex @code{-mapcs-float} command line option, ARM
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@item -mapcs-float
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This indicates the floating point variant of the APCS should be
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used. In this variant floating point arguments are passed in FP
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registers rather than integer registers.
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@cindex @code{-mapcs-reentrant} command line option, ARM
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@item -mapcs-reentrant
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This indicates that the reentrant variant of the APCS should be used.
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This variant supports position independent code.
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@cindex @code{-mfloat-abi=} command line option, ARM
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@item -mfloat-abi=@var{abi}
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This option specifies that the output generated by the assembler should be
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marked as using specified floating point ABI.
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The following values are recognized:
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@code{soft},
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@code{softfp}
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and
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@code{hard}.
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@cindex @code{-eabi=} command line option, ARM
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@item -meabi=@var{ver}
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This option specifies which EABI version the produced object files should
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conform to.
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The following values are recognized:
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@code{gnu},
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@code{4}
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and
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@code{5}.
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@cindex @code{-EB} command line option, ARM
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@item -EB
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This option specifies that the output generated by the assembler should
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be marked as being encoded for a big-endian processor.
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@cindex @code{-EL} command line option, ARM
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@item -EL
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This option specifies that the output generated by the assembler should
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be marked as being encoded for a little-endian processor.
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@cindex @code{-k} command line option, ARM
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@cindex PIC code generation for ARM
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@item -k
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This option specifies that the output of the assembler should be marked
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as position-independent code (PIC).
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@end table
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@node ARM Syntax
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@section Syntax
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@menu
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* ARM-Chars:: Special Characters
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* ARM-Regs:: Register Names
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* ARM-Relocations:: Relocations
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@end menu
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@node ARM-Chars
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@subsection Special Characters
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@cindex line comment character, ARM
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@cindex ARM line comment character
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The presence of a @samp{@@} on a line indicates the start of a comment
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that extends to the end of the current line. If a @samp{#} appears as
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the first character of a line, the whole line is treated as a comment.
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@cindex line separator, ARM
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@cindex statement separator, ARM
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@cindex ARM line separator
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The @samp{;} character can be used instead of a newline to separate
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statements.
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@cindex immediate character, ARM
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@cindex ARM immediate character
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Either @samp{#} or @samp{$} can be used to indicate immediate operands.
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@cindex identifiers, ARM
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@cindex ARM identifiers
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*TODO* Explain about /data modifier on symbols.
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@node ARM-Regs
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@subsection Register Names
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@cindex ARM register names
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@cindex register names, ARM
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*TODO* Explain about ARM register naming, and the predefined names.
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@node ARM Floating Point
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@section Floating Point
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@cindex floating point, ARM (@sc{ieee})
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@cindex ARM floating point (@sc{ieee})
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The ARM family uses @sc{ieee} floating-point numbers.
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@node ARM-Relocations
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@subsection ARM relocation generation
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@cindex data relocations, ARM
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@cindex ARM data relocations
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Specific data relocations can be generated by putting the relocation name
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in parentheses after the symbol name. For example:
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@smallexample
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.word foo(TARGET1)
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@end smallexample
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This will generate an @samp{R_ARM_TARGET1} relocation against the symbol
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@var{foo}.
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The following relocations are supported:
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@code{GOT},
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@code{GOTOFF},
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@code{TARGET1},
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@code{TARGET2},
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@code{SBREL},
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@code{TLSGD},
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@code{TLSLDM},
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@code{TLSLDO},
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@code{GOTTPOFF}
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and
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@code{TPOFF}.
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For compatibility with older toolchains the assembler also accepts
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@code{(PLT)} after branch targets. This will generate the deprecated
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@samp{R_ARM_PLT32} relocation.
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@cindex MOVW and MOVT relocations, ARM
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Relocations for @samp{MOVW} and @samp{MOVT} instructions can be generated
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by prefixing the value with @samp{#:lower16:} and @samp{#:upper16}
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respectively. For example to load the 32-bit address of foo into r0:
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@smallexample
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MOVW r0, #:lower16:foo
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MOVT r0, #:upper16:foo
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@end smallexample
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@node ARM Directives
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@section ARM Machine Directives
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@cindex machine directives, ARM
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@cindex ARM machine directives
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@table @code
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@cindex @code{align} directive, ARM
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@item .align @var{expression} [, @var{expression}]
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This is the generic @var{.align} directive. For the ARM however if the
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first argument is zero (ie no alignment is needed) the assembler will
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behave as if the argument had been 2 (ie pad to the next four byte
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boundary). This is for compatibility with ARM's own assembler.
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@cindex @code{req} directive, ARM
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@item @var{name} .req @var{register name}
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This creates an alias for @var{register name} called @var{name}. For
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example:
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@smallexample
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foo .req r0
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@end smallexample
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@cindex @code{unreq} directive, ARM
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@item .unreq @var{alias-name}
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This undefines a register alias which was previously defined using the
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@code{req}, @code{dn} or @code{qn} directives. For example:
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@smallexample
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foo .req r0
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.unreq foo
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@end smallexample
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An error occurs if the name is undefined. Note - this pseudo op can
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be used to delete builtin in register name aliases (eg 'r0'). This
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should only be done if it is really necessary.
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@cindex @code{dn} and @code{qn} directives, ARM
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@item @var{name} .dn @var{register name} [@var{.type}] [@var{[index]}]
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@item @var{name} .qn @var{register name} [@var{.type}] [@var{[index]}]
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The @code{dn} and @code{qn} directives are used to create typed
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and/or indexed register aliases for use in Advanced SIMD Extension
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(Neon) instructions. The former should be used to create aliases
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of double-precision registers, and the latter to create aliases of
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quad-precision registers.
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If these directives are used to create typed aliases, those aliases can
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be used in Neon instructions instead of writing types after the mnemonic
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or after each operand. For example:
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@smallexample
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x .dn d2.f32
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y .dn d3.f32
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z .dn d4.f32[1]
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vmul x,y,z
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@end smallexample
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This is equivalent to writing the following:
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@smallexample
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vmul.f32 d2,d3,d4[1]
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@end smallexample
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Aliases created using @code{dn} or @code{qn} can be destroyed using
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@code{unreq}.
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@cindex @code{code} directive, ARM
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@item .code @code{[16|32]}
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This directive selects the instruction set being generated. The value 16
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selects Thumb, with the value 32 selecting ARM.
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@cindex @code{thumb} directive, ARM
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@item .thumb
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This performs the same action as @var{.code 16}.
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@cindex @code{arm} directive, ARM
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@item .arm
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This performs the same action as @var{.code 32}.
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@cindex @code{force_thumb} directive, ARM
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@item .force_thumb
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This directive forces the selection of Thumb instructions, even if the
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target processor does not support those instructions
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@cindex @code{thumb_func} directive, ARM
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@item .thumb_func
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This directive specifies that the following symbol is the name of a
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Thumb encoded function. This information is necessary in order to allow
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the assembler and linker to generate correct code for interworking
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between Arm and Thumb instructions and should be used even if
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interworking is not going to be performed. The presence of this
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directive also implies @code{.thumb}
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This directive is not neccessary when generating EABI objects. On these
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targets the encoding is implicit when generating Thumb code.
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@cindex @code{thumb_set} directive, ARM
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@item .thumb_set
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This performs the equivalent of a @code{.set} directive in that it
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creates a symbol which is an alias for another symbol (possibly not yet
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defined). This directive also has the added property in that it marks
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the aliased symbol as being a thumb function entry point, in the same
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way that the @code{.thumb_func} directive does.
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@cindex @code{.ltorg} directive, ARM
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@item .ltorg
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This directive causes the current contents of the literal pool to be
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dumped into the current section (which is assumed to be the .text
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section) at the current location (aligned to a word boundary).
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@code{GAS} maintains a separate literal pool for each section and each
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sub-section. The @code{.ltorg} directive will only affect the literal
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pool of the current section and sub-section. At the end of assembly
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all remaining, un-empty literal pools will automatically be dumped.
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Note - older versions of @code{GAS} would dump the current literal
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pool any time a section change occurred. This is no longer done, since
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it prevents accurate control of the placement of literal pools.
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@cindex @code{.pool} directive, ARM
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@item .pool
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This is a synonym for .ltorg.
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@cindex @code{.fnstart} directive, ARM
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@item .unwind_fnstart
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Marks the start of a function with an unwind table entry.
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@cindex @code{.fnend} directive, ARM
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@item .unwind_fnend
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Marks the end of a function with an unwind table entry. The unwind index
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table entry is created when this directive is processed.
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If no personality routine has been specified then standard personality
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routine 0 or 1 will be used, depending on the number of unwind opcodes
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required.
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@cindex @code{.cantunwind} directive, ARM
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@item .cantunwind
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|
Prevents unwinding through the current function. No personality routine
|
|
or exception table data is required or permitted.
|
|
|
|
@cindex @code{.personality} directive, ARM
|
|
@item .personality @var{name}
|
|
Sets the personality routine for the current function to @var{name}.
|
|
|
|
@cindex @code{.personalityindex} directive, ARM
|
|
@item .personalityindex @var{index}
|
|
Sets the personality routine for the current function to the EABI standard
|
|
routine number @var{index}
|
|
|
|
@cindex @code{.handlerdata} directive, ARM
|
|
@item .handlerdata
|
|
Marks the end of the current function, and the start of the exception table
|
|
entry for that function. Anything between this directive and the
|
|
@code{.fnend} directive will be added to the exception table entry.
|
|
|
|
Must be preceded by a @code{.personality} or @code{.personalityindex}
|
|
directive.
|
|
|
|
@cindex @code{.save} directive, ARM
|
|
@item .save @var{reglist}
|
|
Generate unwinder annotations to restore the registers in @var{reglist}.
|
|
The format of @var{reglist} is the same as the corresponding store-multiple
|
|
instruction.
|
|
|
|
@smallexample
|
|
@exdent @emph{core registers}
|
|
.save @{r4, r5, r6, lr@}
|
|
stmfd sp!, @{r4, r5, r6, lr@}
|
|
@exdent @emph{FPA registers}
|
|
.save f4, 2
|
|
sfmfd f4, 2, [sp]!
|
|
@exdent @emph{VFP registers}
|
|
.save @{d8, d9, d10@}
|
|
fstmdx sp!, @{d8, d9, d10@}
|
|
@exdent @emph{iWMMXt registers}
|
|
.save @{wr10, wr11@}
|
|
wstrd wr11, [sp, #-8]!
|
|
wstrd wr10, [sp, #-8]!
|
|
or
|
|
.save wr11
|
|
wstrd wr11, [sp, #-8]!
|
|
.save wr10
|
|
wstrd wr10, [sp, #-8]!
|
|
@end smallexample
|
|
|
|
@cindex @code{.vsave} directive, ARM
|
|
@item .vsave @var{vfp-reglist}
|
|
Generate unwinder annotations to restore the VFP registers in @var{vfp-reglist}
|
|
using FLDMD. Also works for VFPv3 registers
|
|
that are to be restored using VLDM.
|
|
The format of @var{vfp-reglist} is the same as the corresponding store-multiple
|
|
instruction.
|
|
|
|
@smallexample
|
|
@exdent @emph{VFP registers}
|
|
.vsave @{d8, d9, d10@}
|
|
fstmdd sp!, @{d8, d9, d10@}
|
|
@exdent @emph{VFPv3 registers}
|
|
.vsave @{d15, d16, d17@}
|
|
vstm sp!, @{d15, d16, d17@}
|
|
@end smallexample
|
|
|
|
Since FLDMX and FSTMX are now deprecated, this directive should be
|
|
used in favour of @code{.save} for saving VFP registers for ARMv6 and above.
|
|
|
|
@cindex @code{.pad} directive, ARM
|
|
@item .pad #@var{count}
|
|
Generate unwinder annotations for a stack adjustment of @var{count} bytes.
|
|
A positive value indicates the function prologue allocated stack space by
|
|
decrementing the stack pointer.
|
|
|
|
@cindex @code{.movsp} directive, ARM
|
|
@item .movsp @var{reg} [, #@var{offset}]
|
|
Tell the unwinder that @var{reg} contains an offset from the current
|
|
stack pointer. If @var{offset} is not specified then it is assumed to be
|
|
zero.
|
|
|
|
@cindex @code{.setfp} directive, ARM
|
|
@item .setfp @var{fpreg}, @var{spreg} [, #@var{offset}]
|
|
Make all unwinder annotations relaive to a frame pointer. Without this
|
|
the unwinder will use offsets from the stack pointer.
|
|
|
|
The syntax of this directive is the same as the @code{sub} or @code{mov}
|
|
instruction used to set the frame pointer. @var{spreg} must be either
|
|
@code{sp} or mentioned in a previous @code{.movsp} directive.
|
|
|
|
@smallexample
|
|
.movsp ip
|
|
mov ip, sp
|
|
@dots{}
|
|
.setfp fp, ip, #4
|
|
sub fp, ip, #4
|
|
@end smallexample
|
|
|
|
@cindex @code{.unwind_raw} directive, ARM
|
|
@item .raw @var{offset}, @var{byte1}, @dots{}
|
|
Insert one of more arbitary unwind opcode bytes, which are known to adjust
|
|
the stack pointer by @var{offset} bytes.
|
|
|
|
For example @code{.unwind_raw 4, 0xb1, 0x01} is equivalent to
|
|
@code{.save @{r0@}}
|
|
|
|
@cindex @code{.cpu} directive, ARM
|
|
@item .cpu @var{name}
|
|
Select the target processor. Valid values for @var{name} are the same as
|
|
for the @option{-mcpu} commandline option.
|
|
|
|
@cindex @code{.arch} directive, ARM
|
|
@item .arch @var{name}
|
|
Select the target architecture. Valid values for @var{name} are the same as
|
|
for the @option{-march} commandline option.
|
|
|
|
@cindex @code{.object_arch} directive, ARM
|
|
@item .object_arch @var{name}
|
|
Override the architecture recorded in the EABI object attribute section.
|
|
Valid values for @var{name} are the same as for the @code{.arch} directive.
|
|
Typically this is useful when code uses runtime detection of CPU features.
|
|
|
|
@cindex @code{.fpu} directive, ARM
|
|
@item .fpu @var{name}
|
|
Select the floating point unit to assemble for. Valid values for @var{name}
|
|
are the same as for the @option{-mfpu} commandline option.
|
|
|
|
@cindex @code{.eabi_attribute} directive, ARM
|
|
@item .eabi_attribute @var{tag}, @var{value}
|
|
Set the EABI object attribute number @var{tag} to @var{value}. The value
|
|
is either a @code{number}, @code{"string"}, or @code{number, "string"}
|
|
depending on the tag.
|
|
|
|
@end table
|
|
|
|
@node ARM Opcodes
|
|
@section Opcodes
|
|
|
|
@cindex ARM opcodes
|
|
@cindex opcodes for ARM
|
|
@code{@value{AS}} implements all the standard ARM opcodes. It also
|
|
implements several pseudo opcodes, including several synthetic load
|
|
instructions.
|
|
|
|
@table @code
|
|
|
|
@cindex @code{NOP} pseudo op, ARM
|
|
@item NOP
|
|
@smallexample
|
|
nop
|
|
@end smallexample
|
|
|
|
This pseudo op will always evaluate to a legal ARM instruction that does
|
|
nothing. Currently it will evaluate to MOV r0, r0.
|
|
|
|
@cindex @code{LDR reg,=<label>} pseudo op, ARM
|
|
@item LDR
|
|
@smallexample
|
|
ldr <register> , = <expression>
|
|
@end smallexample
|
|
|
|
If expression evaluates to a numeric constant then a MOV or MVN
|
|
instruction will be used in place of the LDR instruction, if the
|
|
constant can be generated by either of these instructions. Otherwise
|
|
the constant will be placed into the nearest literal pool (if it not
|
|
already there) and a PC relative LDR instruction will be generated.
|
|
|
|
@cindex @code{ADR reg,<label>} pseudo op, ARM
|
|
@item ADR
|
|
@smallexample
|
|
adr <register> <label>
|
|
@end smallexample
|
|
|
|
This instruction will load the address of @var{label} into the indicated
|
|
register. The instruction will evaluate to a PC relative ADD or SUB
|
|
instruction depending upon where the label is located. If the label is
|
|
out of range, or if it is not defined in the same file (and section) as
|
|
the ADR instruction, then an error will be generated. This instruction
|
|
will not make use of the literal pool.
|
|
|
|
@cindex @code{ADRL reg,<label>} pseudo op, ARM
|
|
@item ADRL
|
|
@smallexample
|
|
adrl <register> <label>
|
|
@end smallexample
|
|
|
|
This instruction will load the address of @var{label} into the indicated
|
|
register. The instruction will evaluate to one or two PC relative ADD
|
|
or SUB instructions depending upon where the label is located. If a
|
|
second instruction is not needed a NOP instruction will be generated in
|
|
its place, so that this instruction is always 8 bytes long.
|
|
|
|
If the label is out of range, or if it is not defined in the same file
|
|
(and section) as the ADRL instruction, then an error will be generated.
|
|
This instruction will not make use of the literal pool.
|
|
|
|
@end table
|
|
|
|
For information on the ARM or Thumb instruction sets, see @cite{ARM
|
|
Software Development Toolkit Reference Manual}, Advanced RISC Machines
|
|
Ltd.
|
|
|
|
@node ARM Mapping Symbols
|
|
@section Mapping Symbols
|
|
|
|
The ARM ELF specification requires that special symbols be inserted
|
|
into object files to mark certain features:
|
|
|
|
@table @code
|
|
|
|
@cindex @code{$a}
|
|
@item $a
|
|
At the start of a region of code containing ARM instructions.
|
|
|
|
@cindex @code{$t}
|
|
@item $t
|
|
At the start of a region of code containing THUMB instructions.
|
|
|
|
@cindex @code{$d}
|
|
@item $d
|
|
At the start of a region of data.
|
|
|
|
@end table
|
|
|
|
The assembler will automatically insert these symbols for you - there
|
|
is no need to code them yourself. Support for tagging symbols ($b,
|
|
$f, $p and $m) which is also mentioned in the current ARM ELF
|
|
specification is not implemented. This is because they have been
|
|
dropped from the new EABI and so tools cannot rely upon their
|
|
presence.
|
|
|