From: Nick Desaulniers <ndesaulniers@google.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Fangrui Song <maskray@google.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] objtool: ignore .L prefixed local symbols
Date: Thu, 13 Feb 2020 14:55:47 -0800 [thread overview]
Message-ID: <CAKwvOdnsHMs0PV8uDAWktRDso--_AORNnDYdGHnp5+YYEm1kXw@mail.gmail.com> (raw)
In-Reply-To: <20200213221758.i6pchz4gsiy2lsyc@treble>
On Thu, Feb 13, 2020 at 2:18 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> 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.
Sure thing. I appreciate it, and I'm on board with helping debug or
fix any compiler bugs we might have in order to re-strengthen the
warning soon.
--
Thanks,
~Nick Desaulniers
prev parent reply other threads:[~2020-02-13 22:56 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 18:47 [PATCH] objtool: ignore .L prefixed local symbols Nick Desaulniers
2020-02-13 19:20 ` Fangrui Song
2020-02-14 6:16 ` Arvind Sankar
2020-02-14 18:05 ` Fangrui Song
2020-02-14 20:42 ` Arvind Sankar
2020-02-14 22:20 ` Fangrui Song
2020-02-15 0:05 ` Arvind Sankar
2020-02-15 0:34 ` Arvind Sankar
2020-02-13 22:17 ` Josh Poimboeuf
2020-02-13 22:37 ` Fangrui Song
2020-02-13 23:16 ` Josh Poimboeuf
2020-02-13 22:55 ` Nick Desaulniers [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKwvOdnsHMs0PV8uDAWktRDso--_AORNnDYdGHnp5+YYEm1kXw@mail.gmail.com \
--to=ndesaulniers@google.com \
--cc=clang-built-linux@googlegroups.com \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=maskray@google.com \
--cc=natechancellor@gmail.com \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).