From: Dave Hansen <dave.hansen@intel.com>
To: Ammar Faizi <ammarfaizi2@gnuweeb.org>,
Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Tony Luck <tony.luck@intel.com>,
Yazen Ghannam <yazen.ghannam@amd.com>,
Linux Edac Mailing List <linux-edac@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Stable Kernel <stable@vger.kernel.org>,
GNU/Weeb Mailing List <gwml@vger.gnuweeb.org>,
x86 Mailing List <x86@kernel.org>,
David Laight <David.Laight@ACULAB.COM>,
Jiri Hladky <hladky.jiri@googlemail.com>
Subject: Re: [PATCH v6 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`
Date: Fri, 1 Apr 2022 10:42:48 -0700 [thread overview]
Message-ID: <13463eca-03a2-da0d-c274-fb576a8a051f@intel.com> (raw)
In-Reply-To: <20220329104705.65256-2-ammarfaizi2@gnuweeb.org>
On 3/29/22 03:47, Ammar Faizi wrote:
> The asm constraint does not reflect that the asm statement can modify
> the value of @loops. But the asm statement in delay_loop() does modify
> the @loops.
>
> Specifiying the wrong constraint may lead to undefined behavior, it may
> clobber random stuff (e.g. local variable, important temporary value in
> regs, etc.). This is especially dangerous when the compiler decides to
> inline the function and since it doesn't know that the value gets
> modified, it might decide to use it from a register directly without
> reloading it.
>
> Fix this by changing the constraint from "a" (as an input) to "+a" (as
> an input and output).
Was this found by inspection or was it causing real-world problems?
next prev parent reply other threads:[~2022-04-01 17:42 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-29 10:47 [PATCH v6 0/2] Two x86 fixes Ammar Faizi
2022-03-29 10:47 ` [PATCH v6 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()` Ammar Faizi
2022-04-01 17:42 ` Dave Hansen [this message]
2022-04-02 5:15 ` Ammar Faizi
2022-04-03 16:57 ` Thomas Gleixner
2022-04-03 17:11 ` Ammar Faizi
2022-04-03 17:14 ` Thomas Gleixner
2022-04-05 20:50 ` [tip: x86/misc] x86/delay: Fix the wrong asm constraint in delay_loop() tip-bot2 for Ammar Faizi
2022-03-29 10:47 ` [PATCH v6 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create_bank()` fails Ammar Faizi
2022-04-03 17:03 ` Thomas Gleixner
2022-04-03 17:43 ` Ammar Faizi
2022-04-03 17:45 ` Ammar Faizi
2022-04-03 18:46 ` Borislav Petkov
2022-04-05 20:56 ` [tip: ras/core] x86/MCE/AMD: Fix memory leak when threshold_create_bank() fails tip-bot2 for Ammar Faizi
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