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Mark Wielaard
c0748eff84
There were two issues with bogus sh_addralign values. First we would only check the individual Elf_Data d_align values were powerof2. But not the actual shdr addralign value. This would cause an issue if the shdr addralign was bigger than all of the individual d_align values. Then we could write out a bogus (! powerof2) shdr addralign value for the sections. Secondly when reading in the Elf_Data we would set the d_align value to the value of the shdr addralign value. But we would not check it was valid at all. In practice there are ELF files with incorrect sh_addralign values (they are a powerof2, but aren't aligned to the ELF image offset). We would try to fix that up in elf_update by adding extra padding. But this could bloat the ELF image a lot for large alignment values. So for too large alignments that are bigger than the offset in the ELF file clamp them to the offset value. This could lead us to reject to write out the data again when the offset was not a powerof2. But this will only happen for aligment values bigger than 64. Which are uncommon in practice. Signed-off-by: Mark Wielaard <mjw@redhat.com>
Fundamental design decision: - the sizes of external and internal types are assumed to be the same. This leaves byte ordering aside. While assuming this the code can be greatly simplified and speed increases. Since no change violating this assumption is in sight this is believed to be a worthwhile optimization. - the ABI of the backend modules is not guaranteed. Really, no guarantee whatsoever. We are enforcing this in the code. The modules and their users must match. No third-party EBL module are supported or allowed. The only reason there are separate modules is to not have the code for all architectures in all the binaries. - although the public libraries (libasm, libdw) have a stable API and are backwards ABI compatible they, and the elfutils tools, do depend on each others internals, and on internals of libelf to provide their interfaces. So they should always be upgraded in lockstep when packaging the tools and libraries separately. For one example of how to do that, see the config/elfutils.spec.