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Date:   Sun, 22 Jan 2023 01:40:49 -0800
From:   "H. Peter Anvin" <hpa@zytor.com>
To:     Ammar Faizi <ammarfaizi2@gnuweeb.org>,
        "Li, Xin3" <xin3.li@intel.com>
CC:     Dave Hansen <dave.hansen@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        x86 Mailing List <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: RE: the x86 sysret_rip test fails on the Intel FRED architecture
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References: <SA1PR11MB6734FA9139B9C9F6CC2ED123A8C59@SA1PR11MB6734.namprd11.prod.outlook.com> <5d4ad3e3-034f-c7da-d141-9c001c2343af@intel.com> <18B5DB6D-AEBD-4A67-A7B3-CE64940819B7@zytor.com> <SA1PR11MB673498933098295BFC7C2900A8CB9@SA1PR11MB6734.namprd11.prod.outlook.com> <b6e36a5c-6f5e-eda6-54ad-a0c20eb00402@intel.com> <65D9F1DE-96D4-4CC7-A21C-A740B7DDE0C8@zytor.com> <SA1PR11MB67344F0957245A2BC8CA57B7A8CB9@SA1PR11MB6734.namprd11.prod.outlook.com> <b764c6d8-2a84-27f2-31e2-936c357f8111@gnuweeb.org>
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On January 22, 2023 12:54:56 AM PST, Ammar Faizi <ammarfaizi2@gnuweeb=2Eorg=
> wrote:
>On 1/22/23 3:22 PM, Li, Xin3 wrote:
>> The problem is where/how to set %r11 =3D %rflags in the test code=2E
>>=20
>> The check happens in the USER1 signal handler, and we could set %r11
>> just before calling raise(SIGUSR1)=2E  However, the C library implement=
ation
>> of raise() modifies %r11, thus we can't preserve %r11 until the SYSCALL
>> instruction=2E And the test still fails=2E
>
>From "man 3 raise":
>
>"""
>The raise() function sends a signal to the calling process or thread=2E
>In a single-threaded program it is equivalent to
>
>        kill(getpid(), sig);
>"""
>
>Implementing kill syscall with %r11 modified before entering the kernel
>may look like this?
>
>static void __raise(int sig)
>{
>        __asm__ volatile (
>                "pushf\n\t"
>                "popq %%r11\n\t"
>                "syscall"
>                :
>                : "D"(getpid()),        /* %rdi */
>                  "S"(sig),             /* %rsi */
>                  "a"(__NR_kill)        /* %rax */
>                : "rcx", "r11", "memory"
>        );
>}
>

Exactly=2E