undefined reference to ... when using inline assembly in C

Annie0716 · 07-29-2004, 09:46 PM

I am tring to use assembly inline in C, but errors occured when compiling, the messages are as below, could anyone tell me what' s the causes and how to corrct it?

The code is:
mdct( long *in, long *out) /*sorry, I forget the type, it' s long*/
{
__asm__("

movea in, %a1;
movea out, %a2;
...

");
}

Thank you!

/HHCF5249-HDDMP3-R3/uClinux-dist/lib/zlib -o MP3_ENC main.o bitstream.o formatBitstream.o l3bitstream.o layer3.o l3loop.o tables.o error.o huffman.o l3mdct.o
portableio.o ieeefloat.o l3subband.o reservoir.o wave.o -lm -lc
MP3_ENC.elf2flt: In function `mdct':
/HHCF5249-HDDMP3-R3/uClinux-dist/user/MP3ENC/l3mdct.c:686: undefined reference to `out'
/HHCF5249-HDDMP3-R3/uClinux-dist/user/MP3ENC/l3mdct.c:686: undefined reference to `in'

aluser · 07-29-2004, 09:48 PM

why do *in and *out not have types?

infamous41md · 07-29-2004, 09:53 PM

inline asm doesn't work that way. read the gcc info pages, specifically the section on extended asm to see how to use C variables in asm code. usually it looks like this:

Code:

#define l2b(x) asm("movl %0, %%eax; bswap %%eax; movl %%eax, %1;"   \
                        : "=r" ((x))                                  \
                        : "r" ((x))                                   \
                        : "%eax"                                    \
                )

that swaps the byte order of x. read the info page to see what's going on.

Annie0716 · 08-01-2004, 12:50 AM

Thank you so much!

It worked.