Calling an assembly function from C -

one of generated functions doesn't compute should , trying debug separately. have assembler , try call stripped down c program. however, reason end getting segfaults in function (so, calling function seems work, execution fails). there might wrong passing arguments..

the functions signature is

void func(int, int, float*, float*, float*); 

the function ignores first 2 arguments , received 3 arrays of 32 floats each. add element-wise latter 2 , store result element-wise first array. however, in kind of weird order (as opposed streaming linearly through it, reason doing not in scope of question). that's offset_arrays in assembler code.

i checked x86 calling conventions (that's architecture using) , first 6 integer or pointer arguments passed in registers rdi, rsi, rdx, rcx, r8, , r9.

here' function implementation:

    .text     .globl  func     .align  16, 0x90     .type   func,@function func:     .cfi_startproc     xorl    %eax, %eax     movabsq $offset_array1, %r9     movabsq $offset_array, %r10     xorl    %esi, %esi     .align  16, 0x90 .lbb0_1:     movq    (%r9,%rax), %r11     movq    (%r10,%rax), %rdi     movss   (%r8,%rdi,4), %xmm0     addss   (%rcx,%rdi,4), %xmm0     movss   %xmm0, (%rdx,%r11,4)     incq    %rsi     addq    $8, %rax     cmpq    $33, %rsi     jb  .lbb0_1     retq .ltmp0:     .size   func, .ltmp0-func     .cfi_endproc      .type   offset_array,@object     .section    .rodata,"a",@progbits     .align  16 offset_array:     .quad   0     .quad   16     .quad   1     .quad   17     .quad   2     .quad   18     .quad   3     .quad   19     .quad   4     .quad   20     .quad   5     .quad   21     .quad   6     .quad   22     .quad   7     .quad   23     .quad   8     .quad   24     .quad   9     .quad   25     .quad   10     .quad   26     .quad   11     .quad   27     .quad   12     .quad   28     .quad   13     .quad   29     .quad   14     .quad   30     .quad   15     .quad   31     .size   offset_array, 256      .type   offset_array1,@object     .align  16 offset_array1:     .quad   0     .quad   16     .quad   1     .quad   17     .quad   2     .quad   18     .quad   3     .quad   19     .quad   4     .quad   20     .quad   5     .quad   21     .quad   6     .quad   22     .quad   7     .quad   23     .quad   8     .quad   24     .quad   9     .quad   25     .quad   10     .quad   26     .quad   11     .quad   27     .quad   12     .quad   28     .quad   13     .quad   29     .quad   14     .quad   30     .quad   15     .quad   31     .size   offset_array1, 256       .section    ".note.gnu-stack","",@progbits 

i try call function c code:

float f0[32]; float f1[32]; float f2[32];  extern void func(int i0,int i1,float* dest,float* src0,float* src1);  int main(int argc, char *argv[]) {   func(0,0,f0,f1,f2); } 

compiling both , linking with

gcc -o f.o -c -g f.s gcc -g -o test_f test_f.c f.o 

and running though gdb results in

program received signal sigsegv, segmentation fault. func () @ f.s:17 17      movss   %xmm0, (%rdx,%r11,4) 

so, write memory, namely first array. why segfault , how call function correctly (without changing assembler code)?

the problem comes line

cmpq    $33, %rsi 

it should

cmpq    $32, %rsi 

you accessing junk in memory after .quad 31 , sticking r11 @ movq (%r9,%rax), %r11