Re: segfault in ld.elf_so

[RVP <rvp%SDF.ORG@localhost>]

On Thu, 29 Jan 2026, Thomas Klausner wrote:

> Looking for relro PRs, I found
>
> https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=57792
>
> Could this be related?

Different issue, I think. PR 57792 is a segfault when doing ifunc relocations.
This one seems to be happening when doing the standard PLT relocations.

> (gdb) br main
> Breakpoint 1 at 0x6164
> (gdb) r
> Starting program: .../work/webkitgtk-2.50.4/tmp-introspectyh2m43hy/WebKit2WebExtension-4.1
>
> Program received signal SIGSEGV, Segmentation fault.
> _rtld_relocate_plt_object (obj=<optimized out>, rela=0x793ddd29b7d0, tp=<synthetic pointer>) at /usr/src/libexec/ld.elf_so/arch/x86_64/mdreloc.c:354
> 354                     *where = new_value;
> (gdb) bt
> #0  _rtld_relocate_plt_object (obj=<optimized out>, rela=0x793ddd29b7d0, tp=<synthetic pointer>) at /usr/src/libexec/ld.elf_so/arch/x86_64/mdreloc.c:354
> #1  _rtld_bind (obj=<optimized out>, reloff=<optimized out>) at /usr/src/libexec/ld.elf_so/arch/x86_64/mdreloc.c:372
> #2  0x00007f7ff7cb105d in _rtld_bind_start () from /usr/libexec/ld.elf_so
> #3  0x0000000000000000 in ?? ()

Since the linker crashes way before main() is ever called, what you should do
is:

1. Uncomment the debug defines in the Makefile and set COPTS to `-Og'.

2. Run the program with the new ld.elf_so and collect the (copious) debug
   output.

3. Run `readelf -Wa' on the program and the library it is crashing on when
   doing the PLT reloc. (if, indeed, it's crashing fixing up a library rather
   than the executable).

Post all these outputs.

-RVP