Re: ANNOUNCE: pahole v1.27 (reproducible builds, BTF kfuncs)

Nathan Chancellor
2024-06-13T21:40:21Z

Hi Arnaldo,

On Tue, Jun 11, 2024 at 06:26:53PM -0300, Arnaldo Carvalho de Melo wrote:
> The v1.27 release of pahole and its friends is out, supporting
> parallel reproducible builds and encoding kernel kfuncs in BTF, allowing
> tools such as bpftrace to enumerate the available kfuncs and obtain its
> function signatures and return types.

After commit f632e75 ("dwarf_loader: Add the cu to the cus list early,
remove on LSK_DELETE"), I (and others[1]) notice a crash when running
pahole on modules built with Clang when CONFIG_LTO_CLANG is enabled:

$ curl -LSso .config https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/raw/main/config

$ scripts/config -d LTO_NONE -e LTO_CLANG_THIN

$ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 olddefconfig vmlinux crypto/cast_common.ko
make[3]: *** [scripts/Makefile.modfinal:59: crypto/cast_common.ko] Error 139

I've isolated this to the following commands using the files available
at [2] (these were built with LLVM 18 but I could reproduce it with LLVM
17 and LLVM 19, so it appears to impact a number of versions):

$ tar -tf clang-lto-pahole-1.27-crash.tar.zst
clang-lto-pahole-1.27-crash/
clang-lto-pahole-1.27-crash/cast_common.mod.o
clang-lto-pahole-1.27-crash/module.lds
clang-lto-pahole-1.27-crash/cast_common.o
clang-lto-pahole-1.27-crash/cast_common.ko.bak
clang-lto-pahole-1.27-crash/vmlinux
clang-lto-pahole-1.27-crash/cast_common.ko

$ tar -axf clang-lto-pahole-1.27-crash.tar.zst

$ cd clang-lto-pahole-1.27-crash

$ LLVM_OBJCOPY="llvm-objcopy" pahole-1.26 -J -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func --lang_exclude=rust --btf_base vmlinux cast_common.ko

$ cp cast_common.ko{.bak,}

$ LLVM_OBJCOPY="llvm-objcopy" pahole-1.27 -J -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func --lang_exclude=rust --btf_base vmlinux cast_common.ko
fish: Job 1, '...' terminated by signal SIGSEGV (Address boundary error)

If there is any more information I can provide or patches I can test, I
am more than happy to do so.

[1]: https://gitlab.archlinux.org/archlinux/packaging/packages/pahole/-/issues/1
[2]: https://1drv.ms/u/s!AsQNYeB-IEbqqC2F28JuLy__Q7Vd?e=KsraMU

Cheers,
Nathan