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Message-ID: <20180306163616.7e3b6e0e@vmware.local.home>
Date: Tue, 6 Mar 2018 16:36:16 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Arnd Bergmann <arnd@...db.de>, Ard Biesheuvel
<ard.biesheuvel@...aro.org>, Daniel Micay <danielmicay@...il.com>, Ingo
Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>, Dave Hansen
<dave.hansen@...ux.intel.com>, Alexander Popov <alex.popov@...ux.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, PaX Team
<pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>, Andy
Lutomirski <luto@...nel.org>, Tycho Andersen <tycho@...ho.ws>, Laura Abbott
<labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Borislav Petkov
<bp@...en8.de>, Richard Sandiford <richard.sandiford@....com>, Thomas
Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com>, Peter
Zijlstra <a.p.zijlstra@...llo.nl>, "Dmitry V . Levin" <ldv@...linux.org>,
Emese Revfy <re.emese@...il.com>, Jonathan Corbet <corbet@....net>, Andrey
Ryabinin <aryabinin@...tuozzo.com>, "Kirill A . Shutemov"
<kirill.shutemov@...ux.intel.com>, Thomas Garnier <thgarnie@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>, Alexei Starovoitov
<ast@...nel.org>, Josef Bacik <jbacik@...com>, Masami Hiramatsu
<mhiramat@...nel.org>, Nicholas Piggin <npiggin@...il.com>, Al Viro
<viro@...iv.linux.org.uk>, "David S . Miller" <davem@...emloft.net>, Ding
Tianhong <dingtianhong@...wei.com>, David Woodhouse <dwmw@...zon.co.uk>,
Josh Poimboeuf <jpoimboe@...hat.com>, Dominik Brodowski
<linux@...inikbrodowski.net>, Juergen Gross <jgross@...e.com>, Greg
Kroah-Hartman <gregkh@...uxfoundation.org>, Dan Williams
<dan.j.williams@...el.com>, Mathias Krause <minipli@...glemail.com>, Vikas
Shivappa <vikas.shivappa@...ux.intel.com>, Kyle Huey <me@...ehuey.com>,
Dmitry Safonov <dsafonov@...tuozzo.com>, Will Deacon <will.deacon@....com>,
X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v9 4/7] x86/entry: Erase kernel stack in
syscall_trace_enter()
On Tue, 6 Mar 2018 13:01:20 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> Then the optimization passes will just remove the initialization in
> 99.9% of all cases. Only very occasionally - when gcc cannot see it
> being overwritten - would it remain. And those are exactly the cases
> where you *want* it to remain.
You mean have gcc fill in the variables that it thinks is used
uninitialized with zeros? As long as it still warns about it, because
that usually catches some real bugs where zeroing the variable doesn't
actually fix the bug.
I also tried the example Arnd posted with:
int g(int c)
{
int i;
if (c) /* gcc optimizes out the condition as nothing else sets i */
i = 1;
return i;
}
And he's right. -O2 doesn't warn :-( I think that it should.
-- Steve
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