i#7120: Do not add addend for rela jump slot relocation #7121
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Despite "rela" relocations having an explicit addend value and it being set to non-0 in a new Debian glibc, the addend is assumed to *not* be added to the symbol value when relocating on x86_64 and aarch64 (it does seem to be added on RISCV). This is not obvious and not well documented; we have to just behave like existing loaders behave from experimentation/examination. (Yet another reason to possibly invert the private loader and let the private copy of ld.so do all the loading and relocating: #5437). Tested on a machine where nearly every client test in our suite was crashing after a glibc update: now they pass. Unfortunately it's not simple to make automated tests for this: we don't have an existing framework for relocation testing and it would take non-trivial effort to construct that, beyond the scope of this fix. Fixes #7120
edeiana
approved these changes
Dec 11, 2024
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Despite "rela" relocations having an explicit addend value and it being set to non-0 in a new Debian glibc, the addend is assumed to not be added to the symbol value when relocating on x86_64 and aarch64 (it does seem to be added on RISCV).
This is not obvious and not well documented; we have to just behave like existing loaders behave from experimentation/examination. (Yet another reason to possibly invert the private loader and let the private copy of ld.so do all the loading and relocating: #5437).
Tested on a machine where nearly every client test in our suite was crashing after a glibc update: now they pass. Unfortunately it's not simple to make automated tests for this: we don't have an existing framework for relocation testing and it would take non-trivial effort to construct that, beyond the scope of this fix.
Fixes #7120