Spurious failed to compute relocation: R_PPC64_REL64 in jl_DI_for_fptr

[vchuravy]

Reproducer: https://gist.github.com/vchuravy/1e7b4d9fcca2f5faa0e1cd28480f6e54

Manifests itself as a scary:

  | | |_| | | | (_| |  |  Version 1.5.0-DEV.622 (2020-04-13)
 _/ |\__'_|_|_|\__'_|  |  vc/ppc_llvm9/88c5699df8 (fork: 1 commits, 0 days)
|__/                   |

julia> error()
ERROR: error: failed to compute relocation: R_PPC64_REL64, Invalid data was encountered while parsing the file
error: failed to compute relocation: R_PPC64_REL64, Invalid data was encountered while parsing the file
error: failed to compute relocation: R_PPC64_REL64, Invalid data was encountered while parsing the file

I think those were introduced in 4363c55 (cc: @vtjnash) since they are originating from https://github.com/llvm/llvm-project/blob/bb0e6cc1dd13997e59f3178e27b57f54c11f7f89/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp#L1798-L1804

x-ref: https://github.com/llvm/llvm-project/blob/e0fd87cc64d5102f20219b6bad0e337dc4e6b2d2/llvm/lib/Object/RelocationResolver.cpp#L130-L138

cc: @shirodkara

[vtjnash]

Like the commit message said, I had to change that because LLVM added assertions to prevent us from using the better fast path.

[yuyichao]

https://reviews.llvm.org/D83800 (I'll leave the honor of carrying this patch to someone else since I'm too lazy to track down all the places that needs to be updated, outside this repo...)

So after spending an hour trying to come up with a test case I realized that this case is not actually used in llvm-dwarfdump and seems also not in any other cli tools... So it would have been fine if llvm was lazier......

[vchuravy]

Yeah I can add it to JuliaPackaging/Yggdrasil#1301

[yuyichao]

I can confirm that the issue on aarch64 is fixed for me with the patch.

[MaskRay]

You may need llvm/llvm-project@e0fd87c (llvm-dwarfdump errors -> warnings)

llvm/llvm-project@b922004 added support for R_PPC_REL32 & R_PPC64_REL{32,64}

A larger issue is that llvm-dwarfdump on an object file does not do some linker job so that reasonable addresses are reported.

[vchuravy]

Thanks @MaskRay!