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

Arnaldo Carvalho de Melo
2024-06-17T19:39:40Z

On Thu, Jun 13, 2024 at 02:40:19PM -0700, Nathan Chancellor wrote:
> 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.

I reproduced the problem by just running 'pahole cast_common.ko", so
this isn't even related to the BTF parts, its about the DWARF loader,
I'm on it, thanks for the detailed report and for providing the files.

- Arnaldo

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