[Ltrace-devel] [PATCH v2 0/8] MIPSEL o32 updates

[Petr Machata]

edgar.iglesias at gmail.com writes:

> From: "Edgar E. Iglesias" <edgar at axis.com>
>
> This is the series I've been hacking on.

I pushed this to master.  Thanks for all the work!

> There are still issues with threaded apps.
>
> There are at least two issues:
> 1. Singlestepping over breakpoints is not really thread safe, IIUC.

FWIW, Linux backend takes care of this.  We stop all threads before
singlestepping.  That holds also when arch uses software singlestepping.

The logic for that is declared in sysdeps/linux-gnu/trace.h and
implemented in the corresponding .c, and can be reused by an arch
backend when deemed necessary.  PPC backend does that.

> 2. Waiting until function return until adding breakpoints to
>    resolved addresses is to late and not thread safe.
>
> I plan to take a closer look at the watchpoint approach to eliminate nr 2
> as Petr M suggested. Any suggestions on howto solve issue nr 1 are also
> wellcome. Leaving the breakpoint inplace and emulating the insn might be
> a last resort, but quite involved...

Yeah, GDB calls this displaced stepping.  This would be an interesting
optimization--process under ltrace can perform pretty horibly, with all
the context switches and singlestepping, and this would help a bit.  But
it shouldn't be necessary from strictly the correctnes point of view.

Thanks,
PM