-mabi=name- Generate code for the specified ABI. Permissible values are: ‘apcs-gnu’,
‘atpcs’, ‘aapcs’, ‘aapcs-linux’ and ‘iwmmxt’.
-mapcs-frame- Generate a stack frame that is compliant with the ARM Procedure Call
Standard for all functions, even if this is not strictly necessary for
correct execution of the code. Specifying -fomit-frame-pointer
with this option will cause the stack frames not to be generated for
leaf functions. The default is -mno-apcs-frame.
-mapcs- This is a synonym for -mapcs-frame.
-mthumb-interwork- Generate code which supports calling between the ARM and Thumb
instruction sets. Without this option the two instruction sets cannot
be reliably used inside one program. The default is
-mno-thumb-interwork, since slightly larger code is generated
when -mthumb-interwork is specified.
-mno-sched-prolog- Prevent the reordering of instructions in the function prolog, or the
merging of those instruction with the instructions in the function's
body. This means that all functions will start with a recognizable set
of instructions (or in fact one of a choice from a small set of
different function prologues), and this information can be used to
locate the start if functions inside an executable piece of code. The
default is -msched-prolog.
-mfloat-abi=name- Specifies which floating-point ABI to use. Permissible values
are: ‘soft’, ‘softfp’ and ‘hard’.
Specifying ‘soft’ causes GCC to generate output containing
library calls for floating-point operations.
‘softfp’ allows the generation of code using hardware floating-point
instructions, but still uses the soft-float calling conventions.
‘hard’ allows generation of floating-point instructions
and uses FPU-specific calling conventions.
The default depends on the specific target configuration. Note that
the hard-float and soft-float ABIs are not link-compatible; you must
compile your entire program with the same ABI, and link with a
compatible set of libraries.
-mhard-float- Equivalent to -mfloat-abi=hard.
-msoft-float- Equivalent to -mfloat-abi=soft.
-mlittle-endian- Generate code for a processor running in little-endian mode. This is
the default for all standard configurations.
-mbig-endian- Generate code for a processor running in big-endian mode; the default is
to compile code for a little-endian processor.
-mwords-little-endian- This option only applies when generating code for big-endian processors.
Generate code for a little-endian word order but a big-endian byte
order. That is, a byte order of the form ‘32107654’. Note: this
option should only be used if you require compatibility with code for
big-endian ARM processors generated by versions of the compiler prior to
2.8.
-mcpu=name- This specifies the name of the target ARM processor. GCC uses this name
to determine what kind of instructions it can emit when generating
assembly code. Permissible names are: ‘arm2’, ‘arm250’,
‘arm3’, ‘arm6’, ‘arm60’, ‘arm600’, ‘arm610’,
‘arm620’, ‘arm7’, ‘arm7m’, ‘arm7d’, ‘arm7dm’,
‘arm7di’, ‘arm7dmi’, ‘arm70’, ‘arm700’,
‘arm700i’, ‘arm710’, ‘arm710c’, ‘arm7100’,
‘arm720’,
‘arm7500’, ‘arm7500fe’, ‘arm7tdmi’, ‘arm7tdmi-s’,
‘arm710t’, ‘arm720t’, ‘arm740t’,
‘strongarm’, ‘strongarm110’, ‘strongarm1100’,
‘strongarm1110’,
‘arm8’, ‘arm810’, ‘arm9’, ‘arm9e’, ‘arm920’,
‘arm920t’, ‘arm922t’, ‘arm946e-s’, ‘arm966e-s’,
‘arm968e-s’, ‘arm926ej-s’, ‘arm940t’, ‘arm9tdmi’,
‘arm10tdmi’, ‘arm1020t’, ‘arm1026ej-s’,
‘arm10e’, ‘arm1020e’, ‘arm1022e’,
‘arm1136j-s’, ‘arm1136jf-s’, ‘mpcore’, ‘mpcorenovfp’,
‘arm1156t2-s’, ‘arm1156t2f-s’, ‘arm1176jz-s’, ‘arm1176jzf-s’,
‘cortex-a5’, ‘cortex-a8’, ‘cortex-a9’, ‘cortex-a15’,
‘cortex-r4’, ‘cortex-r4f’, ‘cortex-m4’, ‘cortex-m3’,
‘cortex-m1’,
‘cortex-m0’,
‘xscale’, ‘iwmmxt’, ‘iwmmxt2’, ‘ep9312’.
-mtune=name- This option is very similar to the -mcpu= option, except that
instead of specifying the actual target processor type, and hence
restricting which instructions can be used, it specifies that GCC should
tune the performance of the code as if the target were of the type
specified in this option, but still choosing the instructions that it
will generate based on the CPU specified by a -mcpu= option.
For some ARM implementations better performance can be obtained by using
this option.
-march=name- This specifies the name of the target ARM architecture. GCC uses this
name to determine what kind of instructions it can emit when generating
assembly code. This option can be used in conjunction with or instead
of the -mcpu= option. Permissible names are: ‘armv2’,
‘armv2a’, ‘armv3’, ‘armv3m’, ‘armv4’, ‘armv4t’,
‘armv5’, ‘armv5t’, ‘armv5e’, ‘armv5te’,
‘armv6’, ‘armv6j’,
‘armv6t2’, ‘armv6z’, ‘armv6zk’, ‘armv6-m’,
‘armv7’, ‘armv7-a’, ‘armv7-r’, ‘armv7-m’,
‘iwmmxt’, ‘iwmmxt2’, ‘ep9312’.
-mfpu=name-mfpe=number-mfp=number- This specifies what floating point hardware (or hardware emulation) is
available on the target. Permissible names are: ‘fpa’, ‘fpe2’,
‘fpe3’, ‘maverick’, ‘vfp’, ‘vfpv3’, ‘vfpv3-fp16’,
‘vfpv3-d16’, ‘vfpv3-d16-fp16’, ‘vfpv3xd’, ‘vfpv3xd-fp16’,
‘neon’, ‘neon-fp16’, ‘vfpv4’, ‘vfpv4-d16’,
‘fpv4-sp-d16’ and ‘neon-vfpv4’.
-mfp and -mfpe are synonyms for
-mfpu=‘fpe’number, for compatibility with older versions
of GCC.
If -msoft-float is specified this specifies the format of
floating point values.
If the selected floating-point hardware includes the NEON extension
(e.g. -mfpu=‘neon’), note that floating-point
operations will not be used by GCC's auto-vectorization pass unless
-funsafe-math-optimizations is also specified. This is
because NEON hardware does not fully implement the IEEE 754 standard for
floating-point arithmetic (in particular denormal values are treated as
zero), so the use of NEON instructions may lead to a loss of precision.
-mfp16-format=name- Specify the format of the
__fp16 half-precision floating-point type.
Permissible names are ‘none’, ‘ieee’, and ‘alternative’;
the default is ‘none’, in which case the __fp16 type is not
defined. See Half-Precision, for more information.
-mstructure-size-boundary=n- The size of all structures and unions will be rounded up to a multiple
of the number of bits set by this option. Permissible values are 8, 32
and 64. The default value varies for different toolchains. For the COFF
targeted toolchain the default value is 8. A value of 64 is only allowed
if the underlying ABI supports it.
Specifying the larger number can produce faster, more efficient code, but
can also increase the size of the program. Different values are potentially
incompatible. Code compiled with one value cannot necessarily expect to
work with code or libraries compiled with another value, if they exchange
information using structures or unions.
-mabort-on-noreturn- Generate a call to the function
abort at the end of a
noreturn function. It will be executed if the function tries to
return.
-mlong-calls-mno-long-calls- Tells the compiler to perform function calls by first loading the
address of the function into a register and then performing a subroutine
call on this register. This switch is needed if the target function
will lie outside of the 64 megabyte addressing range of the offset based
version of subroutine call instruction.
Even if this switch is enabled, not all function calls will be turned
into long calls. The heuristic is that static functions, functions
which have the ‘short-call’ attribute, functions that are inside
the scope of a ‘#pragma no_long_calls’ directive and functions whose
definitions have already been compiled within the current compilation
unit, will not be turned into long calls. The exception to this rule is
that weak function definitions, functions with the ‘long-call’
attribute or the ‘section’ attribute, and functions that are within
the scope of a ‘#pragma long_calls’ directive, will always be
turned into long calls.
This feature is not enabled by default. Specifying
-mno-long-calls will restore the default behavior, as will
placing the function calls within the scope of a ‘#pragma
long_calls_off’ directive. Note these switches have no effect on how
the compiler generates code to handle function calls via function
pointers.
-msingle-pic-base- Treat the register used for PIC addressing as read-only, rather than
loading it in the prologue for each function. The run-time system is
responsible for initializing this register with an appropriate value
before execution begins.
-mpic-register=reg- Specify the register to be used for PIC addressing. The default is R10
unless stack-checking is enabled, when R9 is used.
-mcirrus-fix-invalid-insns- Insert NOPs into the instruction stream to in order to work around
problems with invalid Maverick instruction combinations. This option
is only valid if the -mcpu=ep9312 option has been used to
enable generation of instructions for the Cirrus Maverick floating
point co-processor. This option is not enabled by default, since the
problem is only present in older Maverick implementations. The default
can be re-enabled by use of the -mno-cirrus-fix-invalid-insns
switch.
-mpoke-function-name- Write the name of each function into the text section, directly
preceding the function prologue. The generated code is similar to this:
t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov ip, sp
stmfd sp!, {fp, ip, lr, pc}
sub fp, ip, #4
When performing a stack backtrace, code can inspect the value of
pc stored at fp + 0. If the trace function then looks at
location pc - 12 and the top 8 bits are set, then we know that
there is a function name embedded immediately preceding this location
and has length ((pc[-3]) & 0xff000000).
-mthumb- Generate code for the Thumb instruction set. The default is to
use the 32-bit ARM instruction set.
This option automatically enables either 16-bit Thumb-1 or
mixed 16/32-bit Thumb-2 instructions based on the -mcpu=name
and -march=name options. This option is not passed to the
assembler. If you want to force assembler files to be interpreted as Thumb code,
either add a ‘.thumb’ directive to the source or pass the -mthumb
option directly to the assembler by prefixing it with -Wa.
-mtpcs-frame- Generate a stack frame that is compliant with the Thumb Procedure Call
Standard for all non-leaf functions. (A leaf function is one that does
not call any other functions.) The default is -mno-tpcs-frame.
-mtpcs-leaf-frame- Generate a stack frame that is compliant with the Thumb Procedure Call
Standard for all leaf functions. (A leaf function is one that does
not call any other functions.) The default is -mno-apcs-leaf-frame.
-mcallee-super-interworking- Gives all externally visible functions in the file being compiled an ARM
instruction set header which switches to Thumb mode before executing the
rest of the function. This allows these functions to be called from
non-interworking code. This option is not valid in AAPCS configurations
because interworking is enabled by default.
-mcaller-super-interworking- Allows calls via function pointers (including virtual functions) to
execute correctly regardless of whether the target code has been
compiled for interworking or not. There is a small overhead in the cost
of executing a function pointer if this option is enabled. This option
is not valid in AAPCS configurations because interworking is enabled
by default.
-mtp=name- Specify the access model for the thread local storage pointer. The valid
models are soft, which generates calls to
__aeabi_read_tp,
cp15, which fetches the thread pointer from cp15 directly
(supported in the arm6k architecture), and auto, which uses the
best available method for the selected processor. The default setting is
auto.
-mword-relocations- Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
This is enabled by default on targets (uClinux, SymbianOS) where the runtime
loader imposes this restriction, and when -fpic or -fPIC
is specified.
-mfix-cortex-m3-ldrd- Some Cortex-M3 cores can cause data corruption when
ldrd instructions
with overlapping destination and base registers are used. This option avoids
generating these instructions. This option is enabled by default when
-mcpu=cortex-m3 is specified.