Rust on ppc64le: unknown relocation R_PPC64_DTPREL16_LO_DS

[rjzak]

Trying to use Mold with Rust on ppc64le results in this error: unknown relocation: R_PPC64_DTPREL16_LO_DS.

❯ cat .cargo/config 
[target.powerpc64le-unknown-linux-gnu]
linker = "/usr/bin/clang-15"
rustflags = ["-C", "link-arg=--ld-path=/usr/local/bin/mold"]

❯ mold --version
mold 2.4.0 (3d9b4d5c05250fa7c507b0c74038915929f990f1; compatible with GNU ld)

❯ rustc --version
rustc 1.76.0 (07dca489a 2024-02-04)

❯ uname -a
Linux behemoth 6.1.0-17-powerpc64le #1 SMP Debian 6.1.69-1 (2023-12-30) ppc64le GNU/Linux

❯ lsb_release -a
No LSB modules are available.
Distributor ID:	Debian
Description:	Debian GNU/Linux 12 (bookworm)
Release:	12
Codename:	bookworm

I also tried with mold -run cargo build, which gave the same error. The Mold binary installed is the precompiled ppc64le binary from the releases page.

My apologies if this isn't the appropriate place to post this.

[rui314]

Thank you for your report. We can just support that relocation. Let me try doing that next week.

[rjzak]

Awesome! I'm happy to test.

[rui314]

Does the above fix work for you?

[rjzak]

It does not, and I suspect it's because 9f07fd0 added support for R_PPC64_DTPREL16_LO_DS in elf/arch-ppc64v1.cc instead of elf/arch-ppc64v2.cc. My system at least uses ELF v2.

❯ file build/mold
build/mold: ELF 64-bit LSB pie executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld64.so.2, BuildID[sha1]=0cb684a1c6d458b0e653d1542809eff16273d136, for GNU/Linux 3.10.0, not stripped

I tried applying the same thing to elf/arch-ppc64v2.cc and it was a failure:
signal: 11, SIGSEGV: invalid memory reference when compiling my Rust project with the new Mold binary. I also don't know anything about linkers or the details of PPC64 ELF versions!

[rui314]

Is your program open-source? If so, let me know the name of it. I want to try it myself.

[rjzak]

https://github.com/malwaredb/malwaredb-rs

[rui314]

With the above change, cargo test should pass on ppc64le.

[rjzak]

Agreed, it works! Thank you.

[rjzak]

I've been noticing decent speed improvements on my ppc64le workstation, so I became a sponsor :)

[rui314]

Thanks! 😀