linux-kernel - Re: [RFC -tip] x86: introduce ENTRY(KPROBE)_X86 assembly helpers to catch unbalanced declaration

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Message-ID: <20081123223553.GA3066@elte.hu>
Date:	Sun, 23 Nov 2008 23:35:53 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] x86: introduce ENTRY(KPROBE)_X86  assembly helpers
	to catch unbalanced declaration


* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> [Ingo Molnar - Sun, Nov 23, 2008 at 08:31:34PM +0100]
> ...
> | > 
> | > Just got an error in implementation -- we have to support nested
> | > ENTRY without problem. Will check. What a surprise :-)
> | 
> | do you mean:
> | 
> |   ENTRY(system_call)
> |   ENTRY(system_call_after_swapgs)
> |   ...
> |   END(system_call)
> | 
> | that's more of a bug - system_call_after_swapgs is not a real entry 
> | point, we just need the label of it. Perhaps something like __ENTRY() 
> | for that case would be enough.
> | 
> | nor is this one real:
> | 
> |   ENTRY(interrupt)
> |   ENTRY(irq_entries_start)
> |   ...
> |   END(irq_entries_start)
> |   END(interrupt)
> | 
> | do we really need .irq_entries_start?
> | 
> | I think in general we should define a flat hierarchy of entries.
> | 
> | 	Ingo
> | 
> 
> Yeah, I meant these cases. I don't think we really need 
> irq_entries_start (didn't find any mention of them in tree). In case 
> of system_call_after_swapgs I'm not that sure, but since xen use it 
> as a plain jmp (at least now) it could be converted to a plain 
> label. [...]

system_call_after_swapgs is a slowpath and should be converted to a 
simple:

 .globl system_call_after_swapgs
 system_call_after_swapgs:

symbol definition - with no particular jump target alignment tweaks.

(the above sequence should be generalized as an __ENTRY() macro - i.e. 
raw global symbol definition without any alignment tweaks)

	Ingo
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