Feedback-ID: ia2694551:Fastmail
Date: Fri, 9 Feb 2024 09:48:36 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Michael Paquier <michael@paquier.xyz>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
	vignesh C <vignesh21@gmail.com>, torikoshia <torikoshia@oss.nttdata.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Printing backtrace of postgres processes
Message-ID: <202402090848.j6evnpunbehe@alvherre.pgsql>
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On 2024-Feb-09, Michael Paquier wrote:

> Anyway, I've been digging around the signal-safety of backtrace(3)
> (even looking a bit at some GCC code, brrr), and I am under the
> impression that backtrace() is just by nature not safe and also
> dangerous in signal handlers.  One example of issue I've found:
> https://github.com/gperftools/gperftools/issues/838
> 
> This looks like enough ground to me to reject the patch.

Hmm, but the backtrace() manpage says

       •  backtrace() and backtrace_symbols_fd() don't call malloc()  explic‐
          itly,  but  they  are part of libgcc, which gets loaded dynamically
          when first used.  Dynamic loading usually triggers a call  to  mal‐
          loc(3).   If  you  need certain calls to these two functions to not
          allocate memory (in signal handlers, for example), you need to make
          sure libgcc is loaded beforehand.

and the patch ensures that libgcc is loaded by calling a dummy
backtrace() at the start of the process.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"All rings of power are equal,
But some rings of power are more equal than others."
                                 (George Orwell's The Lord of the Rings)