From: Peter Zijlstra <peterz@infradead.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Bernardo Meurer Costa <beme@google.com>,
Nathan Chancellor <nathan@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/extable: prefer local labels in .set directives
Date: Wed, 6 Apr 2022 12:27:51 +0200 [thread overview]
Message-ID: <20220406102751.GA2731@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220329202148.2379697-1-ndesaulniers@google.com>
On Tue, Mar 29, 2022 at 01:21:45PM -0700, Nick Desaulniers wrote:
> Bernardo reported an error that Nathan bisected down to
> (x86_64) defconfig+LTO_CLANG_FULL+X86_PMEM_LEGACY.
>
> LTO vmlinux.o
> ld.lld: error: <instantiation>:1:13: redefinition of 'found'
> .set found, 0
> ^
>
> <inline asm>:29:1: while in macro instantiation
> extable_type_reg reg=%eax, type=(17 | ((0) << 16))
> ^
>
> This appears to be another LTO specific issue similar to what was folded
> into commit 4b5305decc84 ("x86/extable: Extend extable functionality"),
> where the `.set found, 0` in DEFINE_EXTABLE_TYPE_REG in
> arch/x86/include/asm/asm.h conflicts with the symbol for the static
> function `found` in arch/x86/kernel/pmem.c.
>
> Assembler .set directive declare symbols with global visibility, so the
> assembler may not rename such symbols in the event of a conflict. LTO
> could rename static functions if there was a conflict in C sources, but
> it cannot see into symbols defined in inline asm.
>
> The symbols are also retained in the symbol table, regardless of LTO.
>
> Give the symbols .L prefixes making them locally visible, so that they
> may be renamed for LTO to avoid conflicts, and to drop them from the
> symbol table regardless of LTO.
>
> Fixes: 4b5305decc84 ("x86/extable: Extend extable functionality")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1612
> Link: https://sourceware.org/binutils/docs/as/Symbol-Names.html#Local-Symbol-Names
> Reported-by: Bernardo Meurer Costa <beme@google.com>
> Debugged-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Thanks!
next prev parent reply other threads:[~2022-04-06 14:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-29 20:21 [PATCH] x86/extable: prefer local labels in .set directives Nick Desaulniers
2022-03-29 20:41 ` Nathan Chancellor
2022-04-06 10:27 ` Peter Zijlstra [this message]
2022-04-07 9:46 ` [tip: x86/urgent] x86/extable: Prefer " tip-bot2 for Nick Desaulniers
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