Re: [PATCH] [gdbserver] Disable conditional breakpoints on no-hardware-single-step targets

[Antoine Tremblay <antoine dot tremblay at ericsson dot com>]

On 04/30/2015 12:23 PM, Yao Qi wrote:
> From: Yao Qi <yao.qi@linaro.org>
>    /* Define an ARM-mode breakpoint; we only set breakpoints in the C
>       library, which is most likely to be ARM.  If the kernel supports
>       clone events, we will never insert a breakpoint, so even a Thumb
>       C library will work; so will mixing EABI/non-EABI gdbserver and
>       application.  */
> #ifndef __ARM_EABI__
>    (const unsigned char *) &arm_breakpoint,
> #else
>    (const unsigned char *) &arm_eabi_breakpoint,
> #endif
>
> note that the comments are no longer valid as C library can be compiled
> in thumb mode.

Could we update the comments at the same time ?...
> When GDBserver steps over a breakpoint in arm mode function, which
> returns to thumb mode, GDBserver will insert arm mode breakpoint by
> mistake and the program will crash.  GDBserver alone is unable to
> determine the arm/thumb mode given a PC address.  See how GDB does
> it in arm-tdep.c:arm_pc_is_thumb.
>
> After thinking about how to teach GDBserver inserting right breakpoint
> (arm or thumb) for a while, I reconsider it from a different direction
> that it may be unreasonable to run target-side conditional breakpoint for
> targets without hardware single step.  Pedro also pointed this out here
> https://sourceware.org/ml/gdb-patches/2015-04/msg00337.html

I'm looking into teaching gdbserver about inserting the right
breakpoint and possibly software single-step like this post : 
https://sourceware.org/ml/gdb/2012-10/msg00077.html wanted to do...

It would also fix the problem where we would step-over other breakpoints...

But it does seems very complex to say the least, I'm still early in my 
investigation but if you could share your thoughts on how you came to 
think of it as unreasonable to fix arm-mode and possibly the 
single-stepping it would be appreciated ?

Regards,

Antoine Tremblay