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From: Arvind Sankar <nivedita@alum.mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Borislav Petkov <bp@suse.de>, Arnd Bergmann <arnd@arndb.de>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Kalle Valo <kvalo@codeaurora.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: gcc-10: kernel stack is corrupted and fails to boot
Date: Thu, 14 May 2020 01:22:34 -0400	[thread overview]
Message-ID: <20200514052234.GA1894416@rani.riverdale.lan> (raw)
In-Reply-To: <CAHk-=wgiGxRgJGS-zyer1C_x2MQUVo6iZn0=aJyuFTqJWk-mpA@mail.gmail.com>

On Wed, May 13, 2020 at 09:52:07PM -0700, Linus Torvalds wrote:
> On Wed, May 13, 2020, 20:50 Andy Lutomirski <luto@amacapital.net> wrote:
> 
> >
> > LTO isn’t a linker taking regular .o files full of regular machine
> > code and optimizing it. That’s nuts.
> >
> 
> Yeah, you're right. I wear originally thinking just an optimizing
> assembler, and then started thinking about link-time optimizations in that
> sense, but it was wrong to then go from that to LTO which has a very
> specific meaning.
> 
> We do have assemblers that do some optimizations, but they tend to all be
> at the single instruction level (eg things like turning "add $128" into
> "sub $-128" which fits in a byte constant).
> 
>     Linus
> 
> >

The gcc docs [1,2] at least don't inspire much confidence that this will
continue working with plain asm("") though:

"Note that GCC’s optimizers can move asm statements relative to other
code, including across jumps."
...
"Note that the compiler can move even volatile asm instructions relative
to other code, including across jump instructions."

Even if we don't include an instruction in it I think it should at least
have a memory clobber, to stop the compiler from deciding that it can be
moved before the call so it can do the tail-call optimization.

[1] https://gcc.gnu.org/onlinedocs/gcc/Basic-Asm.html#Basic-Asm
[2] https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile

  parent reply	other threads:[~2020-05-14  5:22 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-09 12:06 [PATCH net-next 1/2] ath10k: fix gcc-10 zero-length-bounds warnings Arnd Bergmann
2020-05-09 12:06 ` Arnd Bergmann
2020-05-09 12:06 ` [PATCH net-next 2/2] ath10k: fix ath10k_pci struct layout Arnd Bergmann
2020-05-09 12:06   ` Arnd Bergmann
2020-05-11 12:05   ` Kalle Valo
2020-05-11 12:05     ` Kalle Valo
2020-05-11 12:17     ` Kalle Valo
2020-05-11 12:17       ` Kalle Valo
2020-05-11 12:39       ` Arnd Bergmann
2020-05-11 12:39         ` Arnd Bergmann
2020-05-13  6:50       ` gcc-10: kernel stack is corrupted and fails to boot Kalle Valo
2020-05-13  8:49         ` Arnd Bergmann
2020-05-13 12:45           ` Kalle Valo
2020-05-13 13:45             ` Arnd Bergmann
2020-05-13 15:31               ` Kalle Valo
2020-05-13 16:00                 ` Arnd Bergmann
2020-05-13 16:07                   ` David Laight
2020-05-14  9:13                 ` Harald Arnesen
2020-05-13 15:48         ` Arvind Sankar
2020-05-13 21:28           ` Arnd Bergmann
2020-05-13 21:41             ` Borislav Petkov
2020-05-13 21:49               ` Arnd Bergmann
2020-05-13 22:20                 ` Borislav Petkov
2020-05-13 22:51                   ` Arvind Sankar
2020-05-13 23:13                   ` Linus Torvalds
2020-05-13 23:36                     ` Borislav Petkov
2020-05-14  0:11                       ` Linus Torvalds
2020-05-14  0:51                         ` Nick Desaulniers
2020-05-14  2:20                           ` Linus Torvalds
2020-05-14  3:50                             ` Andy Lutomirski
     [not found]                               ` <CAHk-=wgiGxRgJGS-zyer1C_x2MQUVo6iZn0=aJyuFTqJWk-mpA@mail.gmail.com>
2020-05-14  5:22                                 ` Arvind Sankar [this message]
2020-05-14  8:40                                   ` Arnd Bergmann
2020-05-14 13:27                                     ` [PATCH] x86: Fix early boot crash on gcc-10, third try Borislav Petkov
2020-05-14 14:45                                       ` Kalle Valo
2020-05-14 15:50                                     ` gcc-10: kernel stack is corrupted and fails to boot Arvind Sankar
2020-05-14  8:11                             ` David Laight
2020-05-13 23:07                 ` Linus Torvalds
2020-05-09 15:48 ` [PATCH net-next 1/2] ath10k: fix gcc-10 zero-length-bounds warnings Gustavo A. R. Silva
2020-05-09 15:48   ` Gustavo A. R. Silva
2020-05-11 12:02   ` Kalle Valo
2020-05-11 12:02     ` Kalle Valo
2020-05-11 12:46     ` Arnd Bergmann
2020-05-11 12:46       ` Arnd Bergmann
2020-05-11 13:09       ` Kalle Valo
2020-05-11 13:09         ` Kalle Valo
2020-05-11 13:47         ` Arnd Bergmann
2020-05-11 13:47           ` Arnd Bergmann
2020-05-12  7:33 ` Kalle Valo
2020-05-12  7:33 ` Kalle Valo

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