Re: System call support in process record and replay

[Doug Evans <dje@google.com>]

On Sat, May 30, 2009 at 3:11 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> I have a question about general design of the system call support for
> the record/replay target, for systems whose system calls are entered
> through software interrupts.
>
> The following excerpt from i386-tdep.c shows the currently-only
> implementation, for Linux system calls entered via INT 80h:
>
>    case 0xcd:
>      {
>        int ret;
>        if (target_read_memory (ir.addr, &tmpu8, 1))
>          {
>            if (record_debug)
>              printf_unfiltered (_("Process record: error reading memory "
>                                   "at addr 0x%s len = 1.\n"),
>                                 paddr_nz (ir.addr));
>            return -1;
>          }
>        ir.addr++;
>        if (tmpu8 != 0x80
>            || gdbarch_tdep (gdbarch)->i386_intx80_record == NULL)
>          {
>            printf_unfiltered (_("Process record doesn't support "
>                                 "instruction int 0x%02x.\n"),
>                               tmpu8);
>            ir.addr -= 2;
>            goto no_support;
>          }
>        ret = gdbarch_tdep (gdbarch)->i386_intx80_record (ir.regcache);
>        if (ret)
>          return ret;
>      }
>      break;
>
> Now, suppose there is another x86 target whose system calls are
> entered through 3 software interrupts: 0x10, 0x21, and 0x31.  Does
> this mean that to support such a target, we will need to define 3
> additional members of `struct gdbarch_tdep', one each for every one of
> the above interrupt numbers, and then tweak the above code to call
> each member whenever the corresponding interrupt number is seen in the
> instruction stream?  And adding support for Windows syscalls means
> that yet another member, for INT 2Eh, should be added?  That seems
> rather inelegant and wasteful to me (since these members will go
> unused on every x86 target that does not use those interrupts), but if
> that's the design we want to follow, I'm okay with it.
>

fwiw, I concur.
I'd like to see a lot of this stuff partitioned differently.