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authorAdhemerval Zanella <adhemerval.zanella@linaro.org>2025-02-18 15:58:16 -0500
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2025-03-13 16:50:16 -0300
commit9b646f5dc933dfa019f2ed7f80b6198b43e31f62 (patch)
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elf: Canonicalize $ORIGIN in an explicit ld.so invocation [BZ 25263]
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 requires _fitoa_word and _itoa_word, which for 32-bits pulls a lot of definitions from _itoa.c (due _ITOA_NEEDED being 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> Reviewed-by: Geoffrey Thomas <geofft@ldpreload.com> Tested-by: Geoffrey Thomas <geofft@ldpreload.com>
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