linux-kernel - Re: [PATCH 2/2] x86/cfi,bpf: Fix BPF JIT call

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Message-ID: <CABCJKufBiJjUdmnuy=HkV+dDnZ=xne-OBwPSfJ21RX9c0AzCZw@mail.gmail.com>
Date:   Fri, 1 Dec 2023 15:54:13 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, davem@...emloft.net, dsahern@...nel.org,
        ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, Arnd Bergmann <arnd@...db.de>,
        keescook@...omium.org, nathan@...nel.org, ndesaulniers@...gle.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-arch@...r.kernel.org, llvm@...ts.linux.dev,
        jpoimboe@...nel.org, joao@...rdrivepizza.com, mark.rutland@....com
Subject: Re: [PATCH 2/2] x86/cfi,bpf: Fix BPF JIT call

On Wed, Nov 22, 2023 at 3:15 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> So the kCFI thing is 'new' but readily inspected by objdump or godbolt:
>
>   https://godbolt.org/z/sGe18z3ca
>
> (@Sami, that .Ltmp15 thing, I don't see that in the kernel, what
> compiler flag makes that go away?)

Hmm, that looks like that's what we emit to .kcfi_traps. I suppose
Godbolt just doesn't show the section directives?

https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/X86/kcfi.ll#L30

Sami