From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v3 2/4] x86/syscalls: Specific usage of
 verify_pre_usermode_state
Date: Wed, 22 Mar 2017 13:49:17 -0700
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To: Thomas Garnier <thgarnie@google.com>
Cc: Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@kernel.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, David Howells <dhowells@redhat.com>, Arnd Bergmann <arnd@arndb.de>, Al Viro <viro@zeniv.linux.org.uk>, Dave Hansen <dave.hansen@intel.com>, =?UTF-8?Q?Ren=c3=a9_Nyffenegger?= <mail@renenyffenegger.ch>, Andrew Morton <akpm@linux-foundation.org>, Kees Cook <keescook@chromium.org>, "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>, Andy Lutomirski <luto@kernel.org>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Nicolas Pitre <nicolas.pitre@linaro.org>, Petr Mladek <pmladek@suse.com>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Helge Deller <deller@gmx.de>
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On 03/22/17 13:41, Thomas Garnier wrote:
>>> with the change below for additional feedback.
>>
>> Can you specify what that means?
> 
> If I set inline by default, the compiler chose not to inline it on
> x86. If I force inline the size impact was actually bigger (without
> the architecture specific code).
> 

That's utterly bizarre.  Something strange is going on there.  I suspect
the right thing to do is to out-of-line the error case only, but even
that seems strange.  It should be something like four instructions inline.

>>
>> On x86, where there is only one caller of this, it really seems like it
>> ought to reduce the overhead to almost zero (since it most likely is
>> hidden in the pipeline.)
>>
>> I would like to suggest defining it inline if
>> CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE is set; I really don't
>> care about an architecture which doesn't have it.
> 
> But if there is only one caller, does the compiler is not suppose to
> inline the function based on options?

If it is marked static in the same file, yes, but you have it in a
different file from what I can tell.

> The assembly will call it too, so I would need an inline and a
> non-inline based on the caller.

Where?  I don't see that anywhere, at least for x86.

	-hpa