Newsgroups: comp.os.msdos.djgpp
From: "Pin F. Sun" <pfsun AT undergrad DOT math DOT uwaterloo DOT ca>
Subject: Re: inline assembly - jumps
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Date: Sat, 14 Dec 1996 04:15:16 GMT
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Aaron m Clemmer wrote:
> 
>         Ok, I've been scouring the info files for help, but they don't
> mention this problem, so...
>         I have a function that is declared inline, it has inline assembly
> in it.  It works fine with optimization off, but doesn't compile with it
> on.  The error message is 'symbol not defined', where the symbol is the
> label that I'm trying to jump to.  It only complains when I'm jumping to
> a label prior to the jump instruction.  I tried someones suggestion of
> appending 'b' to 'jnz label1', but that would't compile.  Anyways, here
> is the soure.
> 
> extern __inline__ fixed32 FixedSqrtLP(fixed32 n)
> {
>   fixed32 value=0;
>   __asm__ __volatile__ ("xor %%eax, %%eax \n"
>           "mov $0x40000000, %%ebx \n"
>           "sqrtLP1: mov %%ecx, %%edx \n"   // This is the label that I'm
> jumping to
>           "sub %%ebx, %%edx \n"
>           "jl sqrtLP2 \n"
>           "sub %%eax, %%edx \n"
>           "jl sqrtLP2 \n"
>           "mov %%edx, %%ecx \n"
>           "shr $1, %%eax \n"
>           "or %%ebx, %%eax \n"
>           "shr $2, %%ebx \n"
>           "jnz sqrtLP1 \n"             // this jump won't work
>           "shl $8, %%eax \n"
>           "jmp sqrtLP3 \n"
>         "sqrtLP2: shr $1, %%eax \n"
>         "shr $2, %%ebx \n"
>         "jnz sqrtLP1 \n"        // this one won't either
>         "shl $8, %%eax \n"
>         "sqrtLP3: nop \n"
>           : "=a" (value)
>           : "c" (n)
>           : "eax", "ebx", "ecx", "edx");
>         return value;
> }
> 
> I'm calling it like this:
> 
> int main() {
>  FixedSqrtLP(num);
>  FixedSqrtLP(num);
>  return 0;
> }
> 
> And compile it like this:
> gcc -O3 -o test.exe test.cc
> 
> thanks,
> aaron

I had this problem, too.  Everytime a label is defined before
a jump instruction calls it, the compiler generates error messages.
I've tried things like:

asm (" cmp %edx, $1200
       jge SKIP
       inc edx
       SKIP:
        ...
      ");
No error messages generated if the label is defined after the jump.
I am using DJGPP v2.0, would v2.01 better?