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Date: Wed, 21 Oct 2020 13:30:09 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Sami Tolvanen <samitolvanen@...gle.com>, Jann Horn <jannh@...gle.com>,
the arch/x86 maintainers <x86@...nel.org>,
Masahiro Yamada <masahiroy@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>, Will Deacon <will@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Kees Cook <keescook@...omium.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arch <linux-arch@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
linux-kbuild <linux-kbuild@...r.kernel.org>,
kernel list <linux-kernel@...r.kernel.org>,
linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps
On Wed, Oct 21, 2020 at 11:51:33AM +0200, Peter Zijlstra wrote:
> On Tue, Oct 20, 2020 at 01:52:17PM -0500, Josh Poimboeuf wrote:
> > > arch/x86/lib/retpoline.S:
> > > __x86_retpoline_rdi()+0x10: return with modified stack frame
> > > __x86_retpoline_rdi()+0x0: stack state mismatch: cfa1=7+32 cfa2=7+8
> > > __x86_retpoline_rdi()+0x0: stack state mismatch: cfa1=7+32 cfa2=-1+0
> >
> > Is this with upstream? I thought we fixed that with
> > UNWIND_HINT_RET_OFFSET.
>
> I can't reproduce this one either; but I do get different warnings:
>
> gcc (Debian 10.2.0-13) 10.2.0, x86_64-defconfig:
>
> defconfig-build/vmlinux.o: warning: objtool: __x86_indirect_thunk_rax() falls through to next function __x86_retpoline_rax()
> defconfig-build/vmlinux.o: warning: objtool: .altinstr_replacement+0x1063: (branch)
> defconfig-build/vmlinux.o: warning: objtool: __x86_indirect_thunk_rax()+0x0: (alt)
> defconfig-build/vmlinux.o: warning: objtool: __x86_indirect_thunk_rax()+0x0: <=== (sym)
>
> (for every single register, not just rax)
>
> Which is daft as well, because the retpoline.o run is clean. It also
> doesn't make sense because __x86_retpoline_rax isn't in fact STT_FUNC,
> so WTH ?!
It is STT_FUNC:
SYM_FUNC_START_NOALIGN(__x86_retpoline_\reg)
$ readelf -s vmlinux.o |grep __x86_retpoline_rax
129749: 0000000000000005 17 FUNC GLOBAL DEFAULT 39 __x86_retpoline_rax
--
Josh
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