[MIPS][ELF] Use PC-relative relocations in .eh_frame when possible When compiling position-independent executables, we now use DW_EH_PE_pcrel | DW_EH_PE_sdata4. However, the MIPS ABI does not define a 64-bit PC-relative ELF relocation so we cannot use sdata8 for the large code model case. When using the large code model, we fall back to the previous behaviour of generating absolute relocations. With this change clang-generated .o files can be linked by LLD without having to pass -Wl,-z,notext (which creates text relocations). This is simpler than the approach used by ld.bfd, which rewrites the .eh_frame section to convert absolute relocations into relative references. I saw in D13104 that apparently ld.bfd did not accept pc-relative relocations for MIPS ouput at some point. However, I also checked that recent ld.bfd can process the clang-generated .o files so this no longer seems true. Reviewed By: atanasyan Differential Revision: https://reviews.llvm.org/D72228
Merge commit 8e8ccf47 from llvm git (by me)
[MIPS] Don't emit R_(MICRO)MIPS_JALR relocations against data symbols The R_(MICRO)MIPS_JALR optimization only works when used against functions. Using the relocation against a data symbol (e.g. function pointer) will cause some linkers that don't ignore the hint in this case (e.g. LLD prior to commit 5bab291) to generate a relative branch to the data symbol which crashes at run time. Before this patch, LLVM was erroneously emitting these relocations against local-dynamic TLS function pointers and global function pointers with internal visibility. Reviewers: atanasyan, jrtc27, vstefanovic Reviewed By: atanasyan Differential Revision: https://reviews.llvm.org/D72571
These two changes should allow using lld for MIPS64 (and maybe also MIPS32)
The second commit is not strictly necessary for clang+lld since LLD9 will
not perform the R_MIPS_JALR optimization (it was only added for 10) but it
is probably required in order to use recent ld.bfd.