[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <0b57d2ab-14e0-14a0-adf3-3186fd2f5282@citrix.com>
Date: Wed, 15 Feb 2023 09:17:23 +0000
From: Andrew Cooper <Andrew.Cooper3@...rix.com>
To: Ammar Faizi <ammarfaizi2@...weeb.org>,
"H. Peter Anvin" <hpa@...or.com>
Cc: Dave Hansen <dave.hansen@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Brian Gerst <brgerst@...il.com>,
Borislav Petkov <bp@...en8.de>, Shuah Khan <shuah@...nel.org>,
Ingo Molnar <mingo@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
x86 Mailing List <x86@...nel.org>,
Linux Kselftest Mailing List
<linux-kselftest@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 1/2] selftests/x86: sysret_rip: Handle syscall in a
FRED system
On 26/01/2023 8:08 pm, Ammar Faizi wrote:
> On Mon, Jan 23, 2023 at 05:40:23PM -0800, H. Peter Anvin wrote:
>> So as per Andrew's comment, add:
>>
>> register void * rsp asm("%rsp");
>>
>> ...
>>
>> "+r" (rsp) /* clobber the redzone */
>>
>> ... as the right way to avoid redzone problems.
> I played with this more. I found something wrong with this. This doesn't
> work for me. The compiler still uses red zone despite I use "+r" (rsp).
>
> What did I do wrong?
Well this is a fine mess...
https://godbolt.org/z/MaPM7s8qr does the right thing, but is now
contrary to the prior discussion regarding calls in asm, which concluded
that the "+r"(rsp) was the way to go.
Furthermore GCC regressed in 9.0 and emits:
warning: listing the stack pointer register 'rsp' in a clobber list is
deprecated [-Wdeprecated]
which might be the intention of the developers, but is wrong seeing as
this is the only way to say "I modify the redzone" to the compiler...
~Andrew
Powered by blists - more mailing lists