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From: "palves at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug python/14382] gdb hangs after plotting with matplotlib
Date: Wed, 27 May 2015 18:37:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=14382

--- Comment #21 from Pedro Alves <palves at redhat dot com> ---
Hmm, I guess I'm confused on how blocking the signal on a thread can help. 
AFAICS, the main issue is with libraries changing the SIGCHLD sigaction, which
is process-wide, not per-thread.  So if something sets SA_NOCLDSTOP or SIG_IGN
on SIGCHLD, that applies to the whole process.

I just confirmed now that with SIGCHLD set to SA_NOCLDSTOP or SIG_IGN, nothing
comes out of the signalfd either.

So the workarounds seem to me to be:

 - move ptrace handling to a separate process (either always using gdbserver, 
   or a thinner ptrace wrapper/helper)

 - or perhaps, an evil hack that reimplements sigaction+signal and 
   ignores requests to ignore SIGCHLD.  References to those functions in   
   libraries would resolve to gdb's versions, assuming gdb is not itself 
   a library...

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