On Saturday, January 17 2026, David Bremner wrote:
> On amdahl,
>
> $ cat <<EOF > hello.c
> #include <stdio.h>
> int main(int argc, char **argv){
> printf("hello world\n");
> }
> EOF
>
> $ gdb ./a.out
> Reading symbols from ./a.out...
> (No debugging symbols found in ./a.out)
> (gdb) run
> Starting program: /home/bremner/notmuch-0.39/a.out
>
> Program received signal SIGSEGV, Segmentation fault.
> 0xf7fc682a in ?? () from /lib/ld-linux-armhf.so.3
> (gdb)
>
> I tried 4 executables: /usr/bin/ls, notmuch (compiled from 0.39 and
> 0.40~rc1 source, and hello world). It seems to me that gdb us
> currently unusable on armhf, hence the severity. As always feel free
> to choose a more appropriate severity if I missed something.
Thanks for the bug report.
I can confirm the problem. This has actually happened before in Ubuntu:
https://bugs.launchpad.net/ubuntu/+source/gdb/+bug/1927192
The issue occurs because of an unfortunate combination of how GDB
detects shared library loading (via stap probes on ld.so) and how GDB
tries to detect thumb vs. arm modes. In a nutshell:
- GDB uses SystemTap SDT probes to insert breaking in specific places
inside ld.so.
- These probes reside in a note section inside the ld.so ELF file. GDB
doesn't need symbols to place the breakpoints, *however*
- GDB needs ELF symbols in ld.so in order to determine arm vs. thumb
mode.
- Because we ship a stripped ld.so in Debian, GDB can't make a decision
and defaults to arm mode, which is wrong in this case and causes the
segfault.
The quick workaround here is to install libc6-dbg. This allows GDB to
properly determine the correct mode and adjust the breakpoint on the
inferior accordingly.
This problem is not manifesting on Trixie and earlier releases because
glibc wasn't being built with SystemTap SDT probe support until a few
weeks ago:
https://salsa.debian.org/glibc-team/glibc/-/commit/64d98cedf15c4e1af56855dd0c97c8cf10612920
This means that glibc doesn't have the .note.stapsdt section embedded in
its ELF files, so GDB doesn't even attempt to use the stap probe
mechanism.
Therefore, I am reassigning this bug to glibc because I believe the
correct fix is to ship an unstripped version of ld.so.
Please let me know if you need more details and I'll be happy to provide
them.
Cheers,
--
Sergio
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