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<HTML><HEAD> <TITLE>BBS水木清华站∶精华区</TITLE></HEAD><BODY><CENTER><H1>BBS水木清华站∶精华区</H1></CENTER>MACHINE DEPENDENT OPTIONS <BR> Each of the target machine types can have its own special <BR> options, starting with `-m', to choose among various hard- <BR> ware models or configurations--for example, 68010 vs <BR> 68020, floating coprocessor or none. A single installed <BR> version of the compiler can compile for any model or con- <BR> figuration, according to the options specified. <BR> <BR> Some configurations of the compiler also support addition- <BR> al special options, usually for command-line compatibility <BR> with other compilers on the same platform. <BR> <BR> These are the `-m' options defined for the 68000 series: <BR> <BR> -m68000 <BR> <BR> -mc68000 <BR> Generate output for a 68000. This is the default <BR> when the compiler is configured for 68000-based <BR> systems. <BR> <BR> -m68020 <BR> <BR> -mc68020 <BR> Generate output for a 68020 (rather than a 68000). <BR> This is the default when the compiler is configured <BR> for 68020-based systems. <BR> <BR> -m68881 <BR> Generate output containing 68881 instructions for <BR> floating point. This is the default for most <BR> 68020-based systems unless -nfp was specified when <BR> the compiler was configured. <BR> <BR> -m68030 <BR> Generate output for a 68030. This is the default <BR> when the compiler is configured for 68030-based <BR> systems. <BR> <BR> -m68040 <BR> Generate output for a 68040. This is the default <BR> when the compiler is configured for 68040-based <BR> systems. <BR> <BR> -m68020-40 <BR> Generate output for a 68040, without using any of <BR> the new instructions. This results in code which <BR> can run relatively efficiently on either a <BR> 68020/68881 or a 68030 or a 68040. <BR> <BR> -mfpa Generate output containing Sun FPA instructions for <BR> floating point. <BR> <BR> -msoft-float <BR> Generate output containing library calls for float- <BR> ing point. WARNING: the requisite libraries are <BR> not part of GNU CC. Normally the facilities of the <BR> machine's usual C compiler are used, but this can't <BR> be done directly in cross-compilation. You must <BR> make your own arrangements to provide suitable li- <BR> brary functions for cross-compilation. <BR> <BR> -mshort <BR> Consider type int to be 16 bits wide, like short <BR> int. <BR> <BR> -mnobitfield <BR> Do not use the bit-field instructions. `-m68000' <BR> implies `-mnobitfield'. <BR> <BR> -mbitfield <BR> Do use the bit-field instructions. `-m68020' im- <BR> plies `-mbitfield'. This is the default if you use <BR> the unmodified sources. <BR> <BR> -mrtd Use a different function-calling convention, in <BR> which functions that take a fixed number of argu- <BR> ments return with the rtd instruction, which pops <BR> their arguments while returning. This saves one <BR> instruction in the caller since there is no need to <BR> pop the arguments there. <BR> <BR> This calling convention is incompatible with the <BR> one normally used on Unix, so you cannot use it if <BR> you need to call libraries compiled with the Unix <BR> compiler. <BR> <BR> Also, you must provide function prototypes for all <BR> functions that take variable numbers of arguments <BR> (including printf); otherwise incorrect code will <BR> be generated for calls to those functions. <BR> <BR> In addition, seriously incorrect code will result <BR> if you call a function with too many arguments. <BR> (Normally, extra arguments are harmlessly ignored.) <BR> <BR> The rtd instruction is supported by the 68010 and <BR> 68020 processors, but not by the 68000. <BR>
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