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Sender: Arvind Sankar <niveditas98@gmail.com>
From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Tue, 27 Oct 2020 16:32:10 -0400
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Kees Cook <keescook@chromium.org>,
        Ingo Molnar <mingo@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Peter Collingbourne <pcc@google.com>,
        James Morse <james.morse@arm.com>,
        Borislav Petkov <bp@suse.de>, Ingo Molnar <mingo@redhat.com>,
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        Masahiro Yamada <masahiroy@kernel.org>,
        Arvind Sankar <nivedita@alum.mit.edu>,
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        Josh Poimboeuf <jpoimboe@redhat.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        linux-toolchains@vger.kernel.org
Subject: Re: [PATCH v6 13/29] arm64/build: Assert for unwanted sections
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On Tue, Oct 27, 2020 at 01:28:02PM -0700, Nick Desaulniers wrote:
> > commit 3193c0836f203a91bef96d88c64cccf0be090d9c
> > Author: Josh Poimboeuf <jpoimboe@redhat.com>
> > Date:   Wed Jul 17 20:36:45 2019 -0500
> >
> >     bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()
> >
> > has
> >
> > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code")
> >
> > and mentions objtool and CONFIG_RETPOLINE.
> 
> Thanks for the context.  It might be time to revisit the above commit.
> If I revert it (small conflict that's easy to fixup),
> kernel/bpf/core.o builds cleanly with defconfig+GCC-9.3, so maybe
> obtool did get smart enough to handle that case?  Probably regresses
> the performance of that main dispatch loop for BPF, but not sure what
> folks are expecting when retpolines are enabled.
> -- 
> Thanks,
> ~Nick Desaulniers

The objtool issue was with RETPOLINE disabled.