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Re: SystemTap probes in glibc



Hi,

On 2025-08-28 10:43, Simon Marchi wrote:
> Hello,
> 
> I noticed that Debian's ld-linux.so didn't provide the SystemTap probes
> that allow GDB to get notified of shared library changes, and avoid
> re-reading the whole list from the debugged process all the time.  I saw
> this thread here [1], which, if I understand correctly, ended up in
> disabling the feature because of build failures.  It has been 10 years
> since then, many issues have probably been ironed-out, so I was
> wondering if you would consider trying to enable the feature again, at
> least starting with amd64.

Yes things seems to have stabilized since that moment, at least from a 
few tests things seems to work better now.

> I don't have a pressing need for it.  I'm a GDB developer, I noticed
> some tests behaving differently on my Debian machine than on my other
> non-Debian machine, and it lead me to this observation.  But since it
> helps GDB be a bit more efficient, I think it would be nice to have it
> enabled.

Ok, noted. I'll try to re-enable systemtap support in a future version. 
After discussion, it appears that it will make (cross-)bootstrapping 
debian way more difficult. For that reason, I have been asked to also 
add a build profile to be able to disable that feature.

> According to Luis Machado, GDB expert for the ARM architecture, it's not
> possible to use those probes for ARM, because the probe addresses don't
> carry the Thumb bit.  So it would have to be a feature enabled only for
> certain arches in any case.  For AArch64, it should be fine.

My plan is to enable it on all linux architectures, even if it is not 
useful. I will already have to handle conditional on multiple build 
profile, i don't want to add another layer of complexity.

Regards
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                     http://aurel32.net


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