From: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
To: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Cc: Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Tony Luck <tony.luck@intel.com>,
linux-edac@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"GNU/Weeb Mailing List" <gwml@vger.gnuweeb.org>,
x86@kernel.org, stable@vger.kernel.org,
Jiri Hladky <hladky.jiri@googlemail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v4 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`
Date: Tue, 1 Mar 2022 18:33:54 +0700 [thread overview]
Message-ID: <CAOG64qPgTv5tQNknuG9d-=oL2EPQQ1ys7xu2FoBpNLyzv1qYzA@mail.gmail.com> (raw)
In-Reply-To: <20220301094608.118879-2-ammarfaizi2@gnuweeb.org>
On Tue, Mar 1, 2022 at 4:46 PM Ammar Faizi wrote:
> Fortunately, the constraint violation that's fixed by patch 1 doesn't
> yield any bug due to the nature of System V ABI. Should we backport
> this?
hi sir, it might also be interesting to know that even if it never be
inlined, it's still potential to break.
for example this code (https://godbolt.org/z/xWMTxhTET)
__attribute__((__noinline__)) static void x(int a)
{
asm("xorl\t%%r8d, %%r8d"::"a"(a));
}
extern int p(void);
int f(void)
{
int ret = p();
x(ret);
return ret;
}
translates to this asm
x:
movl %edi, %eax
xorl %r8d, %r8d
ret
f:
subq $8, %rsp
call p
movl %eax, %r8d
movl %eax, %edi
call x
movl %r8d, %eax
addq $8, %rsp
ret
See the %r8d? It should be clobbered by a function call too. But since
no one tells the compiler that we clobber %r8d, it assumes %r8d never
changes after that call. The compiler thinks x() is static and will
not clobber %r8d, even the ABI says %r8d will be clobbered by a
function call. So i think it should be backported to the stable
kernel, it's still a fix
-- Viro
next prev parent reply other threads:[~2022-03-01 11:43 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 9:46 [PATCH v4 0/2] Two x86 fixes Ammar Faizi
2022-03-01 9:46 ` [PATCH v4 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()` Ammar Faizi
2022-03-01 9:54 ` David Laight
2022-03-03 0:14 ` Ammar Faizi
2022-03-01 11:33 ` Alviro Iskandar Setiawan [this message]
2022-03-03 0:06 ` Ammar Faizi
2022-03-03 0:35 ` David Laight
2022-03-01 9:46 ` [PATCH v4 2/2] x86/mce/amd: Fix memory leak when `threshold_create_bank()` fails Ammar Faizi
2022-03-02 17:26 ` Yazen Ghannam
2022-03-02 23:20 ` Ammar Faizi
2022-03-02 23:27 ` Ammar Faizi
2022-03-03 1:58 ` Alviro Iskandar Setiawan
2022-03-03 2:07 ` Ammar Faizi
2022-03-03 2:32 ` Ammar Faizi
2022-03-03 2:51 ` Alviro Iskandar Setiawan
2022-03-07 0:27 ` Ammar Faizi
2022-03-09 20:55 ` Yazen Ghannam
2022-03-10 1:56 ` Ammar Faizi
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