[PATCH v3] elf: Canonicalize $ORIGIN in an explicit ld.so invocation [BZ 25263]

[Florian Weimer]

* Adhemerval Zanella:

> When an executable is invoked directly, we calculate $ORIGIN by calling
> readlink on /proc/self/exe, which the Linux kernel resolves to the
> target of any symlinks.  However, if an executable is run through ld.so,
> we cannot use /proc/self/exe and instead use the path given as an
> argument.  This leads to a different calculation of $ORIGIN, which is
> most notable in that it causes ldd to behave differently (e.g., by not
> finding a library) from directly running the program.
>
> To make the behavior consistent, take advantage of the fact that the
> kernel also resolves /proc/self/fd/ symlinks to the target of any
> symlinks in the same manner, so once we have opened the main executable
> in order to load it, replace the user-provided path with the result of
> calling readlink("/proc/self/fd/N").
>
> (On non-Linux platforms this resolution does not happen and so no
> behavior change is needed.)
>
> The __fd_to_filename usage on loader (through dl-origin.c) pulls
> _itoa.c, which in turn defines a lot of
>
> The __fd_to_filename requires _fitoa_word and _itoa_word, which for
> 32-bits pulls a lot of definitions from _itoa.c (due _ITOA_NEEDED
> debing defined).  To simplify the build move the required function
> to a new file, _fitoa_word.c.
>
> Checked on x86_64-linux-gnu and i686-linux-gnu.
>
> Co-authored-by: Geoffrey Thomas <geofft@ldpreload.com>

This

or

commit 997f49fbadf892136c77115edd537c832fb8074d
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Mon Mar 17 19:08:22 2025 +0000

    elf: Fix tst-origin make rules
    
    Add tests-special before include Rules and compile liborigin.os with
    MODULE_NAME set to testsuite instead of libc.

caused:

/usr/bin/ld: /home/fweimer/src/gnu/glibc/build/libc.so: undefined reference to `__tunable_is_initialized@GLIBC_PRIVATE'

Failing the “make check” build.  I think this happens because the linker
invocation links against system ld.so.

Is there a reason why we can't use the usual test DSO linker invocation?

Thanks,
Florian