Re: [Valgrind-users] unhandled instruction bytes

[Floyd, P. <pj...@wa...>]

On 18/04/2023 17:46, folkert wrote:
> The 2 calls it does are:
>
> print_char:
>      movb (%esi), %al
>      movb %al, buffer
>      movl $4, %eax
>      movl $1, %ebx
>      movl $buffer, %ecx
>      movl $1, %edx
>      int  $0x80
>      ret
>
> exit:
>      movl $1, %eax
>      movl $0, %ebx
>      int  $0x80

Valgrind can't run just any executable binary. It has quite a lot of 
hard coded limitations that correspont (mostly) to what compilers and 
link editors will produce. So if you use assembler and use opcodes not 
normally generated by compilers then it won't work.

The code that handles this is

    case 0xCD: /* INT imm8 */
       d64 = getUChar(delta); delta++;

       /* Handle int $0xD2 (Solaris fasttrap syscalls). */
       if (d64 == 0xD2) {
          jmp_lit(dres, Ijk_Sys_int210, guest_RIP_bbstart + delta);
          vassert(dres->whatNext == Dis_StopHere);
          DIP("int $0xD2\n");
          return delta;
       }
       goto decode_failure;

So int 0x80 results in a decode error.

Can you use syscall?


A+

Paul