RTEMS GNU Tools On-Line Library

M88K Options

Using and Porting the GNU Compiler Collection (GCC)

2.14.11: M88K Options

These `-m' options are defined for Motorola 88k architectures:

-m88000

Generate code that works well on both the m88100 and the m88110.

-m88100

Generate code that works best for the m88100, but that also runs on the m88110.

-m88110

Generate code that works best for the m88110, and may not run on the m88100.

-mbig-pic

Obsolete option to be removed from the next revision. Use `-fPIC'.

-midentify-revision

Include an ident directive in the assembler output recording the source file name, compiler name and version, timestamp, and compilation flags used.

-mno-underscores

In assembler output, emit symbol names without adding an underscore character at the beginning of each name. The default is to use an underscore as prefix on each name.

-mocs-debug-info

-mno-ocs-debug-info

Include (or omit) additional debugging information (about registers used in each stack frame) as specified in the 88open Object Compatibility Standard, ``OCS''. This extra information allows debugging of code that has had the frame pointer eliminated. The default for DG/UX, SVr4, and Delta 88 SVr3.2 is to include this information; other 88k configurations omit this information by default.

-mocs-frame-position

When emitting COFF debugging information for automatic variables and parameters stored on the stack, use the offset from the canonical frame address, which is the stack pointer (register 31) on entry to the function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use `-mocs-frame-position'; other 88k configurations have the default `-mno-ocs-frame-position'.

-mno-ocs-frame-position

When emitting COFF debugging information for automatic variables and parameters stored on the stack, use the offset from the frame pointer register (register 30). When this option is in effect, the frame pointer is not eliminated when debugging information is selected by the -g switch.

-moptimize-arg-area

-mno-optimize-arg-area

Control how function arguments are stored in stack frames. `-moptimize-arg-area' saves space by optimizing them, but this conflicts with the 88open specifications. The opposite alternative, `-mno-optimize-arg-area', agrees with 88open standards. By default GCC does not optimize the argument area.

-mshort-data-num

Generate smaller data references by making them relative to r0, which allows loading a value using a single instruction (rather than the usual two). You control which data references are affected by specifying num with this option. For example, if you specify `-mshort-data-512', then the data references affected are those involving displacements of less than 512 bytes. `-mshort-data-num' is not effective for num greater than 64k.

-mserialize-volatile

-mno-serialize-volatile

Do, or don't, generate code to guarantee sequential consistency of volatile memory references. By default, consistency is guaranteed.

The order of memory references made by the MC88110 processor does not always match the order of the instructions requesting those references. In particular, a load instruction may execute before a preceding store instruction. Such reordering violates sequential consistency of volatile memory references, when there are multiple processors. When consistency must be guaranteed, GNU C generates special instructions, as needed, to force execution in the proper order.

The MC88100 processor does not reorder memory references and so always provides sequential consistency. However, by default, GNU C generates the special instructions to guarantee consistency even when you use `-m88100', so that the code may be run on an MC88110 processor. If you intend to run your code only on the MC88100 processor, you may use `-mno-serialize-volatile'.

The extra code generated to guarantee consistency may affect the performance of your application. If you know that you can safely forgo this guarantee, you may use `-mno-serialize-volatile'.

-msvr4

-msvr3

Turn on (`-msvr4') or off (`-msvr3') compiler extensions related to System V release 4 (SVr4). This controls the following:

Which variant of the assembler syntax to emit.
`-msvr4' makes the C preprocessor recognize `#pragma weak' that is used on System V release 4.
`-msvr4' makes GCC issue additional declaration directives used in SVr4.

`-msvr4' is the default for the m88k-motorola-sysv4 and m88k-dg-dgux m88k configurations. `-msvr3' is the default for all other m88k configurations.

-mversion-03.00

This option is obsolete, and is ignored.

-mno-check-zero-division

-mcheck-zero-division

Do, or don't, generate code to guarantee that integer division by zero will be detected. By default, detection is guaranteed.

Some models of the MC88100 processor fail to trap upon integer division by zero under certain conditions. By default, when compiling code that might be run on such a processor, GNU C generates code that explicitly checks for zero-valued divisors and traps with exception number 503 when one is detected. Use of mno-check-zero-division suppresses such checking for code generated to run on an MC88100 processor.

GNU C assumes that the MC88110 processor correctly detects all instances of integer division by zero. When `-m88110' is specified, both `-mcheck-zero-division' and `-mno-check-zero-division' are ignored, and no explicit checks for zero-valued divisors are generated.

-muse-div-instruction

Use the div instruction for signed integer division on the MC88100 processor. By default, the div instruction is not used.

On the MC88100 processor the signed integer division instruction div) traps to the operating system on a negative operand. The operating system transparently completes the operation, but at a large cost in execution time. By default, when compiling code that might be run on an MC88100 processor, GNU C emulates signed integer division using the unsigned integer division instruction divu), thereby avoiding the large penalty of a trap to the operating system. Such emulation has its own, smaller, execution cost in both time and space. To the extent that your code's important signed integer division operations are performed on two nonnegative operands, it may be desirable to use the div instruction directly.

On the MC88110 processor the div instruction (also known as the divs instruction) processes negative operands without trapping to the operating system. When `-m88110' is specified, `-muse-div-instruction' is ignored, and the div instruction is used for signed integer division.

Note that the result of dividing INT_MIN by -1 is undefined. In particular, the behavior of such a division with and without `-muse-div-instruction' may differ.

-mtrap-large-shift

-mhandle-large-shift

Include code to detect bit-shifts of more than 31 bits; respectively, trap such shifts or emit code to handle them properly. By default GCC makes no special provision for large bit shifts.

-mwarn-passed-structs

Warn when a function passes a struct as an argument or result. Structure-passing conventions have changed during the evolution of the C language, and are often the source of portability problems. By default, GCC issues no such warning.

Using and Porting the GNU Compiler Collection (GCC)