Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 13 Feb 2020 16:17:58 -0600
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     peterz@infradead.org, clang-built-linux@googlegroups.com,
        Nathan Chancellor <natechancellor@gmail.com>,
        Fangrui Song <maskray@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] objtool: ignore .L prefixed local symbols
Message-ID: <20200213221758.i6pchz4gsiy2lsyc@treble>
References: <20200213184708.205083-1-ndesaulniers@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20200213184708.205083-1-ndesaulniers@google.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Feb 13, 2020 at 10:47:08AM -0800, Nick Desaulniers wrote:
> Top of tree LLVM has optimizations related to
> -fno-semantic-interposition to avoid emitting PLT relocations for
> references to symbols located in the same translation unit, where it
> will emit "local symbol" references.
> 
> Clang builds fall back on GNU as for assembling, currently. It appears a
> bug in GNU as introduced around 2.31 is keeping around local labels in
> the symbol table, despite the documentation saying:
> 
> "Local symbols are defined and used within the assembler, but they are
> normally not saved in object files."
> 
> When objtool searches for a symbol at a given offset, it's finding the
> incorrectly kept .L<symbol>$local symbol that should have been discarded
> by the assembler.
> 
> A patch for GNU as has been authored.  For now, objtool should not treat
> local symbols as the expected symbol for a given offset when iterating
> the symbol table.
> 
> commit 644592d32837 ("objtool: Fail the kernel build on fatal errors")
> exposed this issue.

Since I'm going to be dropping 644592d32837 ("objtool: Fail the kernel
build on fatal errors") anyway, I wonder if this patch is still needed?

At least the error will be downgraded to a warning.  And while the
warning could be more user friendly, it still has value because it
reveals a toolchain bug.

-- 
Josh