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From: Thomas Gleixner <[email protected]>
To: Ammar Faizi <[email protected]>, Borislav Petkov <[email protected]>
Cc: Ammar Faizi <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	Dave Hansen <[email protected]>,
	"H. Peter Anvin" <[email protected]>, Ingo Molnar <[email protected]>,
	Tony Luck <[email protected]>,
	Yazen Ghannam <[email protected]>,
	Linux Edac Mailing List <[email protected]>,
	Linux Kernel Mailing List <[email protected]>,
	Stable Kernel <[email protected]>,
	GNU/Weeb Mailing List <[email protected]>,
	x86 Mailing List <[email protected]>,
	David Laight <[email protected]>,
	Jiri Hladky <[email protected]>
Subject: Re: [PATCH v6 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`
Date: Sun, 03 Apr 2022 19:14:34 +0200	[thread overview]
Message-ID: <87tubaks1x.ffs@tglx> (raw)
In-Reply-To: <87zgl2ksu3.ffs@tglx>

On Sun, Apr 03 2022 at 18:57, Thomas Gleixner wrote:
> On Tue, Mar 29 2022 at 17:47, 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.

Ignore me, I misread this part of the explanation.

Thanks,

        tglx

  parent reply	other threads:[~2022-04-03 17:14 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
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 [this message]
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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