linux-kernel - Re: [PATCH bpf] bpf/btf: Accept function names that contain dots

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Date:   Mon, 19 Jun 2023 15:55:58 +0200
From:   Florent Revest <revest@...omium.org>
To:     Eduard Zingerman <eddyz87@...il.com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, martin.lau@...ux.dev, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        nathan@...nel.org, ndesaulniers@...gle.com, trix@...hat.com,
        stable@...r.kernel.org
Subject: Re: [PATCH bpf] bpf/btf: Accept function names that contain dots

On Mon, Jun 19, 2023 at 1:20 PM Florent Revest <revest@...omium.org> wrote:
>
> On Thu, Jun 15, 2023 at 7:05 PM Eduard Zingerman <eddyz87@...il.com> wrote:
> >
> > On Thu, 2023-06-15 at 17:44 +0200, Florent Revest wrote:
> > > An easy reproducer is:
> > >
> > > $ touch pwet.c
> > >
> > > $ clang -g -fsanitize=kernel-address -c -o pwet.o pwet.c
> > > $ llvm-dwarfdump pwet.o | grep module_ctor
> > >
> > > $ clang -fno-integrated-as -g -fsanitize=kernel-address -c -o pwet.o pwet.c
> > > $ llvm-dwarfdump pwet.o | grep module_ctor
> > >                 DW_AT_name      ("asan.module_ctor")
> >
> > Interestingly, I am unable to reproduce it using either
> > clang version 14.0.0-1ubuntu1 or clang main (bd66f4b1da30).
>
> Somehow, I didn't think of trying other clang versions! Thanks, that's
> a good point Eduard. :)
>
> I also can't reproduce it on a 14x build.
>
> However, I seem to be able to reproduce it on main:
>
>   git clone https://github.com/llvm/llvm-project.git
>   mkdir llvm-project/build
>   cd llvm-project/build
>   git checkout bd66f4b1da30
>   cmake -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Release -G
> "Unix Makefiles" ../llvm
>   make -j $(nproc)
>
>   bin/clang -fno-integrated-as -g -fsanitize=kernel-address -c -o
> ~/pwet.o ~/pwet.c
>   bin/llvm-dwarfdump ~/pwet.o | grep module_ctor
>   # Shows module_ctor
>
> I started a bisection, hopefully that will point to something interesting

The bisection pointed to a LLVM patch from Nick in October 2022:
e3bb359aacdd ("[clang][Toolchains][Gnu] pass -g through to assembler")

Based on the context I have, that commit sounds fair enough. I don't
think LLVM does anything wrong here, it seems like BPF should be the
one dealing with dots in function debug info.