Re: PR13901

[Tristan Gingold <gingold at adacore dot com>]

On Apr 2, 2012, at 3:56 PM, Pedro Alves wrote:

> On 04/02/2012 12:57 PM, Tristan Gingold wrote:
> 
>> On Apr 2, 2012, at 12:44 PM, Tristan Gingold wrote:
>>>> On Mar 30, 2012, at 3:42 PM, Jack Howarth wrote:
> 
>>>>>> (gdb) break main
> 
>>>>>> Breakpoint 1 at 0xd80: file himenoBMTxpa.c, line 71.
>>>>>> (gdb) r
>>>>>> Starting program: /Users/howarth/a.out 
>>>>>> darwin_set_sstep: unknown flavour: 4
>>>>>> Error calling thread_get_state for GP registers for thread 0x8451lxwarning:
>>>>>> Mach error at "i386-darwin-nat.c:118" in function
>>>>>> "i386_darwin_fetch_inferior_registers": (os/kern) invalid argument (0x4)
> 
> 
>>>> I now understand the issue:
>>>> 
>>>> gdb spawns bash to run the program, but the bash spawned is 64 bits, which is not understood by gdb...
>> Fixed by this patch (committed on trunk):
> 
> 
> <disclaimer>I don't know much about darwin/osx</disclaimer>
> 
> This assumes there's even a 32-bit version of the user's whatever $SHELL.
> Not sure we can claim that's always true?  It also doesn't feel right
> to force a different $SHELL version/build of the shell that runs if GDB
> is not involved.  Very unlikely to cause problems, but still...

Indeed, this is very unlikely, but I understand the concern.

> Why does GDB need to touch the shell's registers at all in the first place?

I haven't checked why.

> If we can't skip darwin_set_sstep for all continues that are not single-steps,
> we could at least skip those while starting up (when continuing the shell
> until we see enough execs).  That'd suggest a new flag like
> darwin-nat.h:struct private_inferior->starting_up, set and cleared in
> darwin_create_inferior, and then making darwin_resume_thread do:
> 
> -     /* Set single step.  */
> -     inferior_debug (4, _("darwin_set_sstep (thread=%x, enable=%d)\n"),
> -                     thread->gdb_port, step);
> -     darwin_set_sstep (thread->gdb_port, step);
> +     /* Avoid touching the $SHELL process, and go straight to resuming it.  */
> +     gdb_assert (!inf->private->starting_up || !step);
> +     if (!inf->private->starting_up)
> +        {
> +         /* Set single step.  */
> +         inferior_debug (4, _("darwin_set_sstep (thread=%x, enable=%d)\n"),
> +                         thread->gdb_port, step);
> +         darwin_set_sstep (thread->gdb_port, step);
> 
> WDYT?

Yes, it might be cleaner.

Honestly, I'd prefer to get rid of the shell step and directly execute the user program - or at least have an option to do that.  I think I also understand the cons of this approach.

Tristan.