linux-kernel - Re: [PATCH] x86/entry: Improve system call entry comments

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Message-ID: <CALCETrUqvs8BbNBamk88x_Uv3NhRODYr9x5d6+WO4xpRBbeNHw@mail.gmail.com>
Date:	Tue, 8 Mar 2016 10:45:22 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/entry: Improve system call entry comments

On Tue, Mar 8, 2016 at 10:40 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 03/08/16 02:30, Ingo Molnar wrote:
>>>>> + *
>>>>> + * This is considered a slow path.  It is not used by modern libc
>>>>> + * implementations on modern hardware except during process startup.
>>>>> + *
>>>
>>> Sadly I believe Android still uses int $0x80 in the upstream version.
>>
>> I don't see how that fact conflicts with my statement: on 64-bit kernels INT $0x80
>> will (of course) work, but will land on another entry point: entry_INT80_compat(),
>> not entry_INT80_32().
>>
>> On 32-bit kernels the INT $0x80 entry point is entry_INT80_32().
>>
>
> It doesn't.  I was referring to the above quote. Trying to fix that.

s/modern/most, perhaps?

I'm hoping that some day Bionic goes away and gets replaced by musl.

Of course, musl doesn't always use fast syscalls because it needs a
vdso facility that doesn't currently exist.  I'll deal with that
eventually.

>
>         -hpa
>
>



-- 
Andy Lutomirski
AMA Capital Management, LLC