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

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Message-ID: <ZnCQ-Psf_WswMk1W@x1>
Date: Mon, 17 Jun 2024 16:39:36 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: dwarves@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bpf@...r.kernel.org, Alan Maguire <alan.maguire@...cle.com>,
	Jiri Olsa <jolsa@...nel.org>, Jan Engelhardt <jengelh@...i.de>,
	Matthias Schwarzott <zzam@...too.org>,
	Viktor Malik <vmalik@...hat.com>,
	Eduard Zingerman <eddyz87@...il.com>,
	Jan Alexander Steffens <heftig@...hlinux.org>,
	Domenico Andreoli <cavok@...ian.org>,
	Dominique Leuenberger <dimstar@...nsuse.org>,
	Daniel Xu <dxu@...uu.xyz>, Yonghong Song <yonghong.song@...ux.dev>,
	llvm@...ts.linux.dev
Subject: Re: ANNOUNCE: pahole v1.27 (reproducible builds, BTF kfuncs)

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
>