From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Fangrui Song <maskray@google.com>, Arnd Bergmann <arnd@arndb.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <natechancellor@gmail.com>,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH] x86/entry: use STB_GLOBAL for register restoring thunk
Date: Wed, 23 Dec 2020 22:55:02 -0600 [thread overview]
Message-ID: <20201224045502.zkm34cc5srdgpddb@treble> (raw)
In-Reply-To: <20201223232126.759416-1-ndesaulniers@google.com>
On Wed, Dec 23, 2020 at 03:21:26PM -0800, Nick Desaulniers wrote:
> Arnd found a randconfig that produces the warning:
>
> arch/x86/entry/thunk_64.o: warning: objtool: missing symbol for insn at
> offset 0x3e
>
> when building with LLVM_IAS=1 (use Clang's integrated assembler). Josh
> notes:
>
> With the LLVM assembler stripping the .text section symbol, objtool
> has no way to reference this code when it generates ORC unwinder
> entries, because this code is outside of any ELF function.
>
> This behavior was implemented as an optimization in LLVM 5 years ago,
> but it's not the first time this has caused issues for objtool. A patch
> has been authored against LLVM to revert the behavior, which may or may
> not be accepted. Until then use a global symbol for the thunk that way
> objtool can generate proper unwind info here with LLVM_IAS=1.
As Fangrui pointed out, the section symbol stripping is useful for when
there are a ton of sections like '-ffunction-sections' and
'-fdata-sections'. Maybe add that justification to the patch
description.
We can try to support it, though I suspect other tools may also end up
getting surprised.
> Cc: Fangrui Song <maskray@google.com>
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1209
> Link: https://reviews.llvm.org/D93783
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Code looks familiar ;-)
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
--
Josh
next prev parent reply other threads:[~2020-12-24 4:56 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-23 23:21 [PATCH] x86/entry: use STB_GLOBAL for register restoring thunk Nick Desaulniers
2020-12-24 4:55 ` Josh Poimboeuf [this message]
2021-01-06 0:43 ` [PATCH v2] " Nick Desaulniers
2021-01-06 1:58 ` Josh Poimboeuf
2021-01-11 20:38 ` [PATCH v3] x86/entry: emit a symbol " Nick Desaulniers
2021-01-11 20:58 ` Fangrui Song
2021-01-11 22:09 ` Josh Poimboeuf
2021-01-11 22:16 ` Fāng-ruì Sòng
2021-01-11 22:12 ` Josh Poimboeuf
2021-01-12 0:38 ` Borislav Petkov
2021-01-12 0:41 ` Fāng-ruì Sòng
2021-01-12 1:00 ` Borislav Petkov
2021-01-12 1:13 ` Nick Desaulniers
2021-01-12 1:59 ` Josh Poimboeuf
2021-01-12 11:54 ` Borislav Petkov
2021-01-12 19:46 ` [PATCH v4] " Nick Desaulniers
2021-01-12 21:01 ` Mark Brown
2021-01-13 16:59 ` Josh Poimboeuf
2021-01-13 17:46 ` [PATCH] Documentation: asm-annotation: clarify .L local symbol names Nick Desaulniers
2021-01-13 19:56 ` Mark Brown
2021-01-13 17:56 ` [PATCH v4] x86/entry: emit a symbol for register restoring thunk Nick Desaulniers
2021-01-14 10:39 ` Borislav Petkov
2021-01-14 11:36 ` Peter Zijlstra
2021-01-14 13:28 ` [PATCH] x86/entry: Remove put_ret_addr_in_rdi THUNK macro argument Borislav Petkov
2021-01-14 15:53 ` Peter Zijlstra
2021-01-19 10:12 ` [tip: x86/entry] " tip-bot2 for Borislav Petkov
2021-01-14 15:14 ` [PATCH v4] x86/entry: emit a symbol for register restoring thunk Josh Poimboeuf
2021-01-14 11:49 ` [Linux-kernel-mentees] Fwd: " Lukas Bulwahn
2021-01-14 14:21 ` Aditya
2021-01-14 14:35 ` Lukas Bulwahn
2021-01-13 11:52 ` [tip: x86/entry] x86/entry: Emit " tip-bot2 for Nick Desaulniers
2021-01-19 10:12 ` tip-bot2 for Nick Desaulniers
2021-01-12 11:47 ` [PATCH v3] x86/entry: emit " Borislav Petkov
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