Re: Smpeg MMX asm compilation (problem)

[Nick Clifton <nickc at redhat dot com>]

Hi Matt,

> Alright, I've managed to get both .S files to compile- however when I 
> try to link them with a program using:
> extern "C" {
> extern unsigned int cpu_flags(void);
> extern void IDCT_mmx(DCTBLOCK data);
> }
>
> The linker tool comes up with
> ./.libs/libsmpeg.a(parseblock.o): In function `Z8InitIDCTv':
> e:/programming/smpeg/video/parseblock.cpp:117: undefined reference to 
> `cpu_flags()'

Probably because the compiler is adding a prefix of "_" to the 
"cpu_flags" and "IDCT_mmx" symbols.  Check the assembler output of the 
compiler to be sure.

If this is the problem then there are two ways around it:

  1.  Add the "_" prefix to the symbols in the assembler source.  eg:

        .globl _cpu_flags
        .def    _cpu_flags;    .scl   2;      .type 32;    .endef
      _cpu_flags:

  2.  Use the "Asm Labels" feature of gcc to force the correct name to 
be used.  (See the gcc documentation for more details).  eg:

      extern unsigned int cpu_flags (void) asm ("cpu_flags");

Cheers
  Nick