[Bug gdb/16505] internal SIGFPE busy-CPU locks up GDB

["ssbssa at sourceware dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16505

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
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                 CC|                            |ssbssa at sourceware dot org

--- Comment #2 from Hannes Domani <ssbssa at sourceware dot org> ---
(In reply to Sourceware Commits from comment #1)
> The master branch has been updated by Andrew Burgess
> <aburgess@sourceware.org>:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;
> h=fb550a919a88bf4e3950dd7bcdf72f0a18d94206
> 
> commit fb550a919a88bf4e3950dd7bcdf72f0a18d94206
> Author: Andrew Burgess <andrew.burgess@embecosm.com>
> Date:   Thu Jun 10 10:44:43 2021 +0100
> 
>     gdb: terminate upon receipt of SIGFPE
>     
>     GDB's SIGFPE handling is broken, this is PR gdb/16505 and
>     PR gdb/17891.
>     
>     We currently try to use an async event token to process SIGFPE.  So,
>     when a SIGFPE arrives the signal handler calls
>     mark_async_signal_handler then returns, effectively ignoring the
>     signal (for now).
>     
>     The intention is that later the event loop will see that the async
>     token associated with SIGFPE has been marked and will call the async
>     handler, which just throws an error.
>     
>     The problem is that SIGFPE is not safe to ignore.  Ignoring a
>     SIGFPE (unless it is generated artificially, e.g. by raise()) is
>     undefined behaviour, after ignoring the signal on many targets we
>     return to the instruction that caused the SIGFPE to be raised, which
>     immediately causes another SIGFPE to be raised, we get stuck in an
>     infinite loop.  The behaviour is certainly true on x86-64.
>     
>     To view this behaviour I simply added some dummy code to GDB that
>     performed an integer divide by zero, compiled this on x86-64
>     GNU/Linux, ran GDB and saw GDB hang.
>     
>     In this commit, I propose to remove all special handling of SIGFPE and
>     instead just let GDB make use of the default SIGFPE action, that is,
>     to terminate the process.
>     
>     The only user visible change here should be:
>     
>       - If a user sends a SIGFPE to GDB using something like kill,
>         previously GDB would just print an error and remain alive, now GDB
>         will terminate.  This is inline with what happens if the user
>         sends GDB a SIGSEGV from kill though, so I don't see this as an
>         issue.
>     
>       - If a bug in GDB causes a real SIGFPE, previously the users GDB
>         session would hang.  Now the GDB session will terminate.  Again,
>         this is inline with what happens if GDB receives a SIGSEGV due to
>         an internal bug.
>     
>     In bug gdb/16505 there is mention that it would be nice if GDB did
>     more than just terminate when receiving a fatal signal.  I haven't
>     done that in this commit, but later commits will move in that
>     direction.
>     
>     Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16505
>     Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17891

Can this be closed now?

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