These are the ‘-m’ options defined for the Intel IA-16 architecture.
-mtune=cpu-type ¶Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for cpu-type are:
The Intel 8086.
The Intel 8088.
The Intel 80186.
The Intel 80286.
The NEC V20.
The NEC V30.
The NEC V30MZ.
Any CPU listed above. The aim is to generate code which runs reasonably well on any CPU listed above.
As with -mtune=any, but assume a CPU which supports immediate operands for push, imul and shift/rotate instructions.
-march=cpu-type ¶Generate instructions for the machine type cpu-type. The choices for cpu-type are the same as for -mtune. Moreover, specifying -march=cpu-type implies -mtune=cpu-type.
-mmsdos ¶-mr=msdosProduce executables for MS-DOS. This is the default.
-mmsdos-handle-v1 ¶Produce executables for MS-DOS, in such a way that the executables will fail gracefully under MS-DOS version 1.x, rather than crash the system. This option implies -mmsdos.
-mhandle-non-i186If generating code for a machine that supports Intel 80186 instructions (e.g. -march=v30 or -march=i80286), insert code to check, at startup, whether the code is indeed running on an 80186-capable system.
This requires support from the C library, and currently only works when targeting MS-DOS.
-mhandle-non-i286If generating code for a machine that supports Intel 80286 instructions, (e.g. -march=i80286), insert code to check, at startup, whether the code is indeed running on an 80286-capable system.
This requires support from the C library, and currently only works when targeting MS-DOS.
-mcmodel=tiny ¶Generate code for the tiny code model, with a single combined data and text segment in a 64 KiB address space. This is the default for MS-DOS.
-mcmodel=small ¶-mseparate-code-segmentGenerate code for the small code model, with one data segment and one text segment, in separate 64 KiB spaces. This is now (February 2020) the default for ELKS (-melks), and also (February 2022) the default for DOS extender mode (-mdosx, -mdosx32).
At the compile stage, -mcmodel=small currently disables trampolines for nested functions.
At the linking stage—unless -T is used—this option also causes
GCC to switch to a different output format to better support separate
segments. In particular, if targeting MS-DOS, GCC will produce an MZ
executable. (This requires support from the linker script which comes with
the C library.)
-msegment-relocation-stuff ¶-mno-segment-relocation-stuffEnable (or disable) language features, such as static pointers to far variables, that rely on segment relocations to work. If the small code model or medium code model is used, outside of DOS extender mode (-mdosx, -mdosx32), the default is to allow such language features.
-mshort-jumps ¶-mno-short-jumpsAllow (or disallow) the use of jump instructions which can only jump −128/+127 bytes. The default is not to use them. This option only affects instructions for which the assembler doesn’t provide a work-around and the compiler doesn’t know the jump displacement.
-mrtd ¶-mstdcallUse a different function-calling convention, in which functions that
take a fixed number of arguments return with the ret num
instruction, which pops their arguments while returning. This saves one
instruction in the caller since there is no need to pop the arguments
there.
At the linking stage, this option will also make GCC link your code against the appropriate -mrtd multilib.
You can specify that an individual function is called with this calling
sequence with the function attribute stdcall. You can also
override the -mrtd option by using the function attribute
cdecl or regparmcall. See IA-16 Function Attributes.
Warning: you must provide function prototypes for all functions that
take variable numbers of arguments (including printf);
otherwise incorrect code is generated for calls to those
functions.
In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored. See Default IA-16 Calling Convention.)
-mregparmcall ¶Use a different function-calling convention, in which functions receive
their first few arguments in the registers ax, dx, and
cx, and pop their remaining arguments off the stack. An exception is
that, if the number of arguments to a function is variable, the ...
variable arguments will always go on the stack, and the calling function
pops all pushed arguments.
At the linking stage, -mregparmcall will also make GCC link your code against the appropriate -mregparmcall multilib.
You can specify that an individual function is called with this calling
sequence with the function attribute regparmcall. You can also
override the -mregparmcall option by using the function attribute
cdecl or stdcall. See IA-16 Function Attributes.
Warning: you must provide function prototypes for all functions that
take variable numbers of arguments (including printf);
otherwise incorrect code is generated for calls to those
functions.
In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.)
-mno-callee-assume-ds-data-segment ¶-mcallee-assume-ds-data-segmentUse (or do not use) a different function-calling convention, in which the
ds register is not assumed to point to the program’s data segment
(the generic address space) at function entry, and is treated as just an
ordinary call-used register (with -fcall-used-ds) or fixed
register (-ffixed-ds) with no special meaning.
The ss register is still assumed to point to the data segment—data
items in the generic address space will be accessed via ss.
This option is ignored if ds is set to be a call-saved register
(-fcall-saved-ds).
In the default configuration (-mcallee-assume-ds-data-segment
-mcallee-assume-ss-data-segment -fcall-used-ds), functions can assume that
ds points to the program’s data segment at function entry, and will
arrange to reset ds to ss—if needed—just before returning.
You can override this option for individual functions, by using the
assume_ds_data and no_assume_ds_data function attributes.
See IA-16 Function Attributes.
-mprotected-mode ¶Enable partial support for generating code to run in Intel 80286 protected mode.
With this option, the output code will avoid using segment registers
(ds, es) to hold arbitrary 16-bit values—in protected mode,
doing so may make the CPU crash the program. Instead, the output code will
only load segment registers when dereferencing near or far pointers.
Currently, -mprotected-mode also causes GCC to avoid placing
asm operands in segment registers. You can tell GCC to let an
operand go into a segment register, by passing the operand through a
built-in function ‘__builtin_ia16_selector’:
void foo (unsigned selector)
{
__asm volatile ("nop"
: : "e" (__builtin_ia16_selector (selector)));
}
Note: if you are writing protected mode code that will run in a freestanding environment, it is advised to also specify both -mprotected-mode and -ffreestanding at link time, so that GCC will link your code with a version of libgcc that can work in protected mode.
-mno-newlib-autofloat-stdio ¶If using the Newlib C library, do not try to detect whether the program needs
floating-point support in the formatted I/O routines (stdio). In
particular, -mno-newlib-autofloat-stdio without
-mnewlib-nano-stdio tells GCC to always include floating-point
support.
Without this option, GCC will try to detect if such support is needed, and
link against the appropriate version of the stdio code.
If you use this option, specify it at compile time and during the final link.
-mdosx ¶-mdpmiProduce MS-DOS executables which run under a DOS extender in protected mode. The executables will use the DOS Protected Mode Interface (DPMI) to switch to protected mode, if they detect a DPMI host.
This option requires support from the linker script which comes with the C library. It implies -mmsdos, -march=i80286, and -mprotected-mode, and currently also enables -msegelf.
-mdosx32 ¶Similar to -mdosx, but the MS-DOS executables will be “dual mode” programs which can operate under both 16- and 32-bit DPMI hosts. 16-bit programs will try to start in 32-bit DPMI mode whenever possible.
This switch is mainly for experimentation purposes.
-melks ¶-mr=elks-melks-libcProduce executables for the Embeddable Linux Kernel Subset (ELKS) operating system. In addition, link against ELKS’s own C runtime library—which must be built with GCC, and installed—instead of the Newlib C library.
This option implies -mprotected-mode and -mcmodel=small, and currently also enables -msegelf and -fuse-ld=gold.
-mr=rt ¶Produce executables for the specified target runtime environment rt, if the necessary runtime libraries and support files are installed.
-maout-stack=stack-size ¶-mstack-size=stack-sizeWhen building an ELKS program (-melks), set it to request the operating system to reserve at least stack-size bytes in the data segment for the stack. This requires support from the linker back-end and from the linker script which comes with the C library.
-maout-heap=heap-size ¶When building an ELKS program (-melks), set it to request the operating system to reserve at least heap-size bytes in the data segment for the heap.
When building an MS-DOS program, set it to limit the size of the heap to heap-size bytes.
This option requires support from the linker back-end and from the linker script which comes with the C library.
-mcmodel=medium ¶Generate code for the medium code model, with one data segment and multiple text segments, each in a separate 64 KiB space.
At the linking stage—unless -T is used—this option will also make GCC link your code against the appropriate medium model multilib, and switch to the appropriate output program format.
This option is currently not supported for C++. Also, medium model support for the ELKS target is incomplete.
-mnewlib-nano-stdio ¶If using the Newlib C library, link against a limited version of the
formatted I/O routines (stdio) which supports only C89 functionality
and by default excludes floating-point support.
-mtsr ¶Emit and link with extra code to support the writing of MS-DOS terminate-and-stay-resident (TSR) programs. The -maout-heap= option can be used to adjust the maximum size of the program’s resident heap.
If you use this option, specify it at compile time and during the final link.
This option implies -mmsdos, and requires support from the linker script which comes with the C library.
-msegelf ¶Generate object files which follow H. Peter Anvin’s proposed 16-bit segmented code ABI, https://git.zytor.com/users/hpa/segelf/abi.git/plain/segelf.txt. This is now (September 2020) the default for ELKS (-melks).
Warning: The -msegelf switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries.
-mno-callee-assume-ss-data-segment ¶Use a different function-calling convention, in which the ss register
is not assumed to point to the program’s data segment at function entry.
This option exists only for testing.
-masm=intel ¶Output assembly instructions using Intel syntax, rather than the default
AT&T syntax. This also affects
which dialect is used for basic asm (see Basic Asm — Assembler Instructions Without Operands) and
extended asm (see Extended Asm - Assembler Instructions with C Expression Operands).
-mno-post-link ¶After running the linker, skip any post-link steps which may be needed to transform the linker output into a usable target executable. The output from -mno-post-link will likely be an intermediate ELF file.
This switch is mainly for experimentation purposes.
-maout-total=total ¶When building an ELKS program (-melks), set it to request the operating system to set the top of the data segment—including static storage, heap, stack, and environment variables—to at least total. This requires support from the linker back-end and from the linker script which comes with the C library.
-maout-chmem=chmem ¶When building an ELKS program (-melks), set it to request the operating system to reserve at least chmem bytes in the data segment for non-static storage (such as heap, stack, and environment variables). This requires support from the linker back-end and from the script which comes with the C library.
-mfar-function-if-far-return-type ¶This option is ignored. It exists only for compatibility with older build systems.
__FAR__SEG_SSEach of these macros is defined only if the compiler supports the named address space specifier (see IA-16 Named Address Spaces).
__SEGMENTThis macro is defined only if the compiler supports the Watcom-compatible
__segment type name.
__CDECL__STDCALL__PASCAL__INTERRUPT__LOADDS__SAVEREGSEach of these macros is defined only if the compiler supports the
corresponding lowercase Watcom-compatible type qualifier, e.g.,
__cdecl. The type qualifiers may themselves be macros defined in
terms of function attributes (see IA-16 Function Attributes).
Regarding the __saveregs qualifier, note that Open Watcom and Borland
C++ 4.0 define it to mean different things:
__saveregs means to save only segment registers.
__saveregs means to save all registers, except
possibly registers which hold return values.
GCC currently follows Borland’s stricter meaning.
__IA16_CMODEL_TINY____TINY____IA16_CMODEL_SMALL____SMALL____IA16_CMODEL_MEDIUM____MEDIUM__Each of these macros is defined only if the named code model (tiny, small, or medium) is selected.
__IA16_ARCH_ANY__IA16_ARCH_ANY_186__IA16_ARCH_I8086__IA16_ARCH_I8088__IA16_ARCH_NEC_V30__IA16_ARCH_NEC_V30MZ__IA16_ARCH_NEC_V20__IA16_ARCH_I80186__IA16_ARCH_I80188__IA16_ARCH_I80286These macros are defined according to the -march=cpu-type option settings.
__IA16_TUNE_ANY__IA16_TUNE_ANY_186__IA16_TUNE_I8086__IA16_TUNE_I8088__IA16_TUNE_NEC_V30__IA16_TUNE_NEC_V30MZ__IA16_TUNE_NEC_V20__IA16_TUNE_I80186__IA16_TUNE_I80188__IA16_TUNE_I80286These macros are defined according to the -mtune=cpu-type and option settings.
__IA16_FEATURE_SHIFT_IMM__IA16_FEATURE_PUSH_IMM__IA16_FEATURE_IMUL_IMM__IA16_FEATURE_PUSHA__IA16_FEATURE_ENTER_LEAVE__IA16_FEATURE_AAD_IMM__IA16_FEATURE_FSTSW_AXEach of these macros is defined only if the CPU selected by -march=cpu-type supports the named type of IA-16 instruction.
__IA16_FEATURE_SHIFT_MASKEDThis macro is defined only if the selected CPU’s bitwise shift and rotation
instructions—rcl, shr, and so on—implicitly mask each
shift count to their lower 5 bits.
__IA16_FEATURE_PROTECTED_MODEThis macro is defined only if -mprotected-mode is in effect.
__IA16_FEATURE_DPMIABLEThis macro is defined only if -mdpmiable is in effect.
__IA16_FEATURE_ALLOCABLE_DS_REGThis macro is defined only if the ds register is configured to be
available for register allocation—that is, it is either call-used or
call-saved, not fixed.
__IA16_FEATURE_FAR_FUNCTION_SYNTAXThis macro is defined only if the postfix __far syntax for declaring
far functions is supported (see IA-16 Named Address Spaces).
__IA16_CALLCVT_FAR_FUNCTION_IF_FAR_RETURN_TYPEThis macro is defined only if the classical syntax for declaring far functions is supported (see IA-16 Named Address Spaces).
__IA16_FEATURE_FAR_STATIC_STORAGEThis macro is defined only if static storage variables can be placed in
__far space (see IA-16 Named Address Spaces).
__IA16_FEATURE_ATTRIBUTE_CDECL__IA16_FEATURE_ATTRIBUTE_STDCALL__IA16_FEATURE_ATTRIBUTE_REGPARMCALL__IA16_FEATURE_ATTRIBUTE_PASCAL__IA16_FEATURE_ATTRIBUTE_ASSUME_DS_DATA__IA16_FEATURE_ATTRIBUTE_NO_ASSUME_DS_DATA__IA16_FEATURE_ATTRIBUTE_SAVE_DS__IA16_FEATURE_ATTRIBUTE_NO_SAVE_DS__IA16_FEATURE_ATTRIBUTE_SAVE_ES__IA16_FEATURE_ATTRIBUTE_SAVE_ALL__IA16_FEATURE_ATTRIBUTE_ASSUME_SS_DATA__IA16_FEATURE_ATTRIBUTE_NO_ASSUME_SS_DATA__IA16_FEATURE_ATTRIBUTE_NEAR_SECTION__IA16_FEATURE_ATTRIBUTE_FAR_SECTION__IA16_FEATURE_ATTRIBUTE_INTERRUPTEach of these macros is defined only if the corresponding function attribute is recognized (see IA-16 Function Attributes). If the compiler knows about an attribute but does not fully support it, the macro will be defined with a value of 0.
__BUILTIN_IA16_SELECTOR__BUILTIN_IA16_FP_OFF__BUILTIN_IA16_STATIC_FAR_CAST__BUILTIN_IA16_NEAR_DATA_SEGMENT__BUILTIN_IA16_SSEach of these macros is defined only if the corresponding
__builtin_ia16_… macro is defined (see IA-16 Built-in Functions).
By default, GCC outputs code for this calling convention:
ax, bx, cx, and dx are call-used.
si, di, bp, and es are call-saved.
ds is a special case. Both ds and ss are assumed to
point to the program’s data segment on entry, and ds should be
restored on exit. A function is free to modify ds, but it should
restore it to its initial value—perhaps via a ‘pushw %ss; popw
%ds’—before calling another function, and before returning to its caller.