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From: Xin Li <xin@zytor.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	kernel test robot <lkp@intel.com>,
	linux-kernel@vger.kernel.org
Cc: oe-kbuild-all@lists.linux.dev, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
	x86@kernel.org, hpa@zytor.com, peterz@infradead.org,
	stable@vger.kernel.org
Subject: Re: [PATCH v1 1/1] x86/fred/signal: Prevent single-step upon ERETU completion
Date: Thu, 22 May 2025 23:23:30 -0700	[thread overview]
Message-ID: <98baeeed-345d-4ae9-9418-61df6c689516@zytor.com> (raw)
In-Reply-To: <005d4d4c-f385-42e0-8a30-62c6d77ff0f0@citrix.com>

>>>      arch/x86/include/asm/sighandling.h: In function
>>> 'prevent_single_step_upon_eretu':
>>>>> arch/x86/include/asm/sighandling.h:44:21: error: 'struct pt_regs'
>>>>> has no member named 'fred_ss'
>>>         44 |                 regs->fred_ss.swevent = 0;
>>>            |                     ^~
>>>
>>
>> Hmm, this statement is under IS_ENABLED(CONFIG_X86_FRED), which should
>> be a compile time FALSE with i386.  Why it is still being compiled?
> 
> Because what the compiler is seeing is:
> 
> if (0 && ...)
>      regs->fred_ss.swevent = 0;
> 
> and the bad field name is found at parse time, while the whole
> expression is only discarded during optimisation.
> 
> The one thing you can't IS_ENABLED() around is conditional fields.  That
> needs to be full #ifdef.

Thanks a lot for the explanation.  Just sent out v3 using #ifdef.

     Xin

  reply	other threads:[~2025-05-23  6:24 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-05-22  6:05 Xin Li (Intel)
2025-05-22  7:20 ` H. Peter Anvin
2025-05-22 17:10   ` Xin Li
2025-05-22 17:20 ` kernel test robot
2025-05-22 17:33   ` Xin Li
2025-05-22 17:51     ` Andrew Cooper
2025-05-23  6:23       ` Xin Li [this message]
2025-05-22 17:54     ` Dave Hansen
2025-05-23  6:24       ` Xin Li

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