[cfe-dev] Has something changed in variadic function call ABI...?

[Fons Rademakers]

Hi,

  the trunk version fails in executing code that used to work a few weeks 
ago for code that constructs variadic function calls in x86_64. Here an 
example of our code (which is generated by a function call stub generator 
for our interpreter):

   ...
   // put arguments in dval, or lval or u[]
   ...
   ...
   long fptr = (long)&Printf;   // <--- our variadic function
   __asm__ __volatile__("movlpd %0, %%xmm0"  :: "m" (dval[0]) : "%xmm0");
   __asm__ __volatile__("movlpd %0, %%xmm1"  :: "m" (dval[1]) : "%xmm1");
   __asm__ __volatile__("movlpd %0, %%xmm2"  :: "m" (dval[2]) : "%xmm2");
   __asm__ __volatile__("movlpd %0, %%xmm3"  :: "m" (dval[3]) : "%xmm3");
   __asm__ __volatile__("movlpd %0, %%xmm4"  :: "m" (dval[4]) : "%xmm4");
   __asm__ __volatile__("movlpd %0, %%xmm5"  :: "m" (dval[5]) : "%xmm5");
   __asm__ __volatile__("movlpd %0, %%xmm6"  :: "m" (dval[6]) : "%xmm6");
   __asm__ __volatile__("movlpd %0, %%xmm7"  :: "m" (dval[7]) : "%xmm7");
   __asm__ __volatile__("movq %0, %%rdi" :: "m" (lval[0]) : "%rdi");
   __asm__ __volatile__("movq %0, %%rsi" :: "m" (lval[1]) : "%rsi");
   __asm__ __volatile__("movq %0, %%rdx" :: "m" (lval[2]) : "%rdx");
   __asm__ __volatile__("movq %0, %%rcx" :: "m" (lval[3]) : "%rcx");
   __asm__ __volatile__("movq %0, %%r8"  :: "m" (lval[4]) : "%r8");
   __asm__ __volatile__("movq %0, %%r9"  :: "m" (lval[5]) : "%r9");
   __asm__ __volatile__("movq %0, %%r10" :: "m" (fptr) : "%r10");
   // (umax+2)*8 = 176
   __asm__ __volatile__("subq $176, %rsp");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 0(%%rsp)" :: "m" (u[0].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 8(%%rsp)" :: "m" (u[1].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 16(%%rsp)" :: "m" (u[2].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 24(%%rsp)" :: "m" (u[3].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 32(%%rsp)" :: "m" (u[4].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 40(%%rsp)" :: "m" (u[5].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 48(%%rsp)" :: "m" (u[6].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 56(%%rsp)" :: "m" (u[7].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 64(%%rsp)" :: "m" (u[8].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 72(%%rsp)" :: "m" (u[9].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 80(%%rsp)" :: "m" (u[10].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 88(%%rsp)" :: "m" (u[11].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 96(%%rsp)" :: "m" (u[12].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 104(%%rsp)" :: "m" (u[13].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 112(%%rsp)" :: "m" (u[14].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 120(%%rsp)" :: "m" (u[15].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 128(%%rsp)" :: "m" (u[16].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 136(%%rsp)" :: "m" (u[17].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 144(%%rsp)" :: "m" (u[18].lval) : "%rax");
   __asm__ __volatile__("movq %0, %%rax \n\t"
                        "movq %%rax, 152(%%rsp)" :: "m" (u[19].lval) : "%rax");
   __asm__ __volatile__("movl $8, %eax");  // number of used xmm registers
   __asm__ __volatile__("call *%r10");
   __asm__ __volatile__("addq $176, %rsp");
   __asm__ __volatile__("movq %%rax, %0" : "=m" (u[0].lval) :: "memory"); 
// get return value
   __asm__ __volatile__("movq %%rdi, %0" : "=m" (u[1].lval) :: "memory"); 
// get return value (icc C++ object)
       G__letint(result7, 67, (long) u[0].lval);
    return(1 || funcname || hash || result7 || libp) ;
}

with the trunk version this call into Printf() fails. While it used to work 
and while it still works with gcc 4.1 - 4.5. Does anybody know if something 
in the area has changed on purpose or if this is a regression?


Cheers, Fons.


-- 
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