SOSP'13 Question from Presenter (Xi Wang)

dis

disassemble mul

log

➜ sosp_question>make
gcc question.c -o question -Wall -Werror -O0 -fno-inline -g
gdb -x dis -batch ./question
Dump of assembler code for function mul:
   0x0000000000400544 <+0>:	push   %rbp
   0x0000000000400545 <+1>:	mov    %rsp,%rbp
   0x0000000000400548 <+4>:	mov    %edi,%edx
   0x000000000040054a <+6>:	mov    %esi,%eax
   0x000000000040054c <+8>:	mov    %dx,-0x14(%rbp)
   0x0000000000400550 <+12>:	mov    %ax,-0x18(%rbp)
   0x0000000000400554 <+16>:	movzwl -0x14(%rbp),%edx
   0x0000000000400558 <+20>:	movzwl -0x18(%rbp),%eax
   0x000000000040055c <+24>:	imul   %edx,%eax
   0x000000000040055f <+27>:	mov    %eax,-0x4(%rbp)
   0x0000000000400562 <+30>:	mov    -0x4(%rbp),%eax
   0x0000000000400565 <+33>:	pop    %rbp
   0x0000000000400566 <+34>:	retq   
End of assembler dump.
./question
Testing arguments: 0xffff 0xffff
result (function return): 0xfffe0001
result (variable): 0xfffe0001
gcc question.c -o question -Wall -Werror -O1 -fno-inline -g
gdb -x dis -batch ./question
Dump of assembler code for function mul:
   0x0000000000400564 <+0>:	movzwl %di,%edi
   0x0000000000400567 <+3>:	movzwl %si,%esi
   0x000000000040056a <+6>:	mov    %edi,%eax
   0x000000000040056c <+8>:	imul   %esi,%eax
   0x000000000040056f <+11>:	retq   
End of assembler dump.
./question
Testing arguments: 0xffff 0xffff
result (function return): 0xfffe0001
result (variable): 0xfffe0001
gcc question.c -o question -Wall -Werror -O2 -fno-inline -g
gdb -x dis -batch ./question
Dump of assembler code for function mul:
   0x00000000004005e0 <+0>:	movzwl %di,%edi
   0x00000000004005e3 <+3>:	movzwl %si,%esi
   0x00000000004005e6 <+6>:	mov    %edi,%eax
   0x00000000004005e8 <+8>:	imul   %esi,%eax
   0x00000000004005eb <+11>:	retq   
End of assembler dump.
./question
Testing arguments: 0xffff 0xffff
result (function return): 0xfffe0001
result (variable): 0xfffe0001
gcc question.c -o question -Wall -Werror -O3 -fno-inline -g
gdb -x dis -batch ./question
Dump of assembler code for function mul:
   0x00000000004005e0 <+0>:	movzwl %di,%edi
   0x00000000004005e3 <+3>:	movzwl %si,%esi
   0x00000000004005e6 <+6>:	mov    %edi,%eax
   0x00000000004005e8 <+8>:	imul   %esi,%eax
   0x00000000004005eb <+11>:	retq   
End of assembler dump.
./question
Testing arguments: 0xffff 0xffff
result (function return): 0xfffe0001
result (variable): 0xfffe0001

Makefile

default:
	gcc question.c -o question -Wall -Werror
	./question

question.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

uint64_t mul(uint16_t a, uint16_t b)
{
    uint32_t ret = a * b;
    return ret;
}

int main(int argc, char* argv[])
{
    uint64_t result = 0;

    fprintf(stdout, "Testing arguments: 0x%x 0x%x\n", 0xffff, 0xffff);
    result = mul(0xffff, 0xffff);
    fprintf(stdout, "result (function return): 0x%lx\n", mul(0xffff, 0xffff));
    fprintf(stdout, "result (variable): 0x%lx\n", result);

    return EXIT_SUCCESS;
}