From adrian at openwork.nz  Sun Oct  1 20:47:52 2023
From: adrian at openwork.nz (Adrian Cochrane)
Date: Mon, 2 Oct 2023 09:47:52 +1300
Subject: Advice on diagnosing segfaults?
Message-ID: <84fa2100-6657-006f-0957-3a344f3f3c80@openwork.nz>

Hi,

I've got a segfault in one of the language bindings I'm developing 
(fontconfig-pure), and I'm struggling to locate it.

I see it occur in another project calling the language binding (so 
unfortunately I don't know what exactly is causing it), but GDB tells me 
that it occurs within a particular function I'm language binding to (and 
nothing more). I've attempted a few theoretical fixes without 
improvement (beyond triggering an infinite loop instead). And setting a 
breakpoint on the wrapper-function I added to create a better ABI to 
language bind to shows that dozens (if not more) of these calls 
successfully before I hit the segfault.

I'm not sure how to diagnose this issue, any help would be appreciated!

Cheers,

Adrian Cochrane

OpenWork Ltd

libdggs spatial analysis

Rhapsode & Haphaestus web browsers


From lemming at henning-thielemann.de  Sun Oct  1 20:59:18 2023
From: lemming at henning-thielemann.de (Henning Thielemann)
Date: Sun, 1 Oct 2023 22:59:18 +0200 (CEST)
Subject: Advice on diagnosing segfaults?
In-Reply-To: <84fa2100-6657-006f-0957-3a344f3f3c80@openwork.nz>
References: <84fa2100-6657-006f-0957-3a344f3f3c80@openwork.nz>
Message-ID: <7789447d-e520-4ffd-925f-f2fa37da9891@henning-thielemann.de>


On Mon, 2 Oct 2023, Adrian Cochrane wrote:

> I've got a segfault in one of the language bindings I'm developing 
> (fontconfig-pure), and I'm struggling to locate it.

I could solve some problems in my C library bindings using ltrace. It logs 
all calls to external C libraries together with the function parameters. 
You can create a config file in order to improve reporting of passed 
parameters.

Another useful tool might be valgrind. I think it should also point you to 
the crashing function call.