Re: [Qemu-devel] [PATCH 0/2] linux-user: Don't call gdb_handlesig unnecessarily

[Richard Henderson <richard.henderson@linaro.org>]

On 10/19/18 10:49 AM, Peter Maydell wrote:
> This patchset fixes a minor bug in our handling of SIGTRAP
> in linux-user.
> 
> The CPU main-loop routines for linux-user generally call
> gdb_handlesig() when they're about to queue a SIGTRAP signal.  This
> is wrong, because queue_signal() will cause us to pend a signal, and
> process_pending_signals() will then call gdb_handlesig() itself.  So
> the effect is that we notify gdb of the SIGTRAP, and then if gdb says
> "OK, continue with signal X" we will incorrectly notify gdb of the
> signal X as well.  We don't do this double-notify for anything else,
> only SIGTRAP.
> 
> This bug only manifests if the user responds to the reported SIGTRAP
> using "signal SIGFOO" rather than "continue"; since the latter is the
> overwhelmingly common thing to do after a breakpoint most people
> won't have hit this.
> 
> Patch 1 fixes this bug for every target except nios2, by
> deleting the incorrect code.
> 
> Patch 2 fixes nios2 separately, because it was doing some odd
> things with gdb_handlesig(). This also fixes in passing a Coverity
> issue.
> 
> Tested with "make check-tcg", and with some by-hand stepping
> around with an attached gdb. NB that the nios2 patch is only
> compile tested as I don't have a nios2 linux-user environment
> and check-tcg doesn't cover it.
> 
> thanks
> -- PMM
> 
> Peter Maydell (2):
>   linux-user: Don't call gdb_handlesig() before queue_signal()
>   linux-user: Clean up nios2 main loop signal handling

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


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