boot_stage2: improve reproducibility #1907
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Specifying the final boot2 source file as a link library here causes the final `.elf` to be linked directly with that `.S`, which causes it to be compiled into an object file with a name like `/tmp/<random chars>.o`. This temporary object name is embedded in the final `.elf`, so the `.elf`'s contents change after each link even if none of the input files change, breaking reproducibility. Fix the issue by specifying the source file as the source for an object-only library, then specifying the library's object files as the target link libraries, so the source is compiled in a separate step and only the object is passed to the linker.
kilograham
approved these changes
Sep 11, 2024
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Specifying the final boot2 source file as a link library here causes the final
.elfto be linked directly with that.S, which causes it to be compiled into an object file with a name like/tmp/<random chars>.o. This temporary object name is embedded in the final.elf, so the.elf's contents change after each link even if none of the input files change, breaking reproducibility.Fix the issue by specifying the source file as the source for an object-only library, then specifying the library's object files as the target link libraries, so the source is compiled in a separate step and only the object is passed to the linker.
Fixes #1906
This makes everything fully reproducible for me and my setup though I have not tested exhaustively and reproducibility is of course something that can't be absolutely proved. Also please keep in mind I'm not knowledgeable with CMake and bumbled into this solution.