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[patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant

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[view original message]
From: Cyrill Gorcunov <gorcunov@...>
To: <ak@...>, <mingo@...>, <sam@...>, <tglx@...>, <hpa@...>, <linux-kernel@...>
Cc: Cyrill Gorcunov <gorcunov@...>
Subject: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 11:17 am

Though we use PDA for regular task stack but that

is not acceptable for init_task wich is special

one. We still have to allocate init_task's stack

in that manner.


Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

---


Ingo, Peter, I can be wrong but take a look please

to x86/lgest/i386_head.S:41


	/* Set up the initial stack so we can run C code. */

	movl $(init_thread_union+THREAD_SIZE),%esp


if we just eliminate this string from lds scripts - I bet

we get bad situation here. Xen has a similar trick.

And even head_32.S and head_64.S both have


32bits

======

ENTRY(stack_start)

	.long init_thread_union+THREAD_SIZE


64bits

======

	ENTRY(init_rsp)

	.quad  init_thread_union+THREAD_SIZE-8


So if we just remove that string from lds file - we will

be screwed up I think ;)


Index: linux-2.6.git/arch/x86/kernel/vmlinux_64.lds.S

===================================================================

--- linux-2.6.git.orig/arch/x86/kernel/vmlinux_64.lds.S	2008-02-17 13:56:54.000000000 +0300

+++ linux-2.6.git/arch/x86/kernel/vmlinux_64.lds.S	2008-02-17 14:10:21.000000000 +0300

@@ -129,7 +129,7 @@ SECTIONS

 #undef VVIRT_OFFSET

 #undef VVIRT


-  . = ALIGN(8192);		/* init_task */

+  . = ALIGN(THREAD_SIZE);	/* init_task */

   .data.init_task : AT(ADDR(.data.init_task) - LOAD_OFFSET) {

 	*(.data.init_task)

   }:data.init


--

--
[view original message]
From: Sam Ravnborg <sam@...>
To: Cyrill Gorcunov <gorcunov@...>
Cc: <ak@...>, <mingo@...>, <tglx@...>, <hpa@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 2:59 pm

hpa had some comments about this particular alignment.

If we keep the alignmnet then Cyrill's patch looks good.


But maybe we should check what is the real alignmment

requirement (outside the scope of wha you do - someone

more intiminate with this coide should do it).


	Sam

--
[view original message]
From: Ingo Molnar <mingo@...>
To: Sam Ravnborg <sam@...>
Cc: Cyrill Gorcunov <gorcunov@...>, <ak@...>, <tglx@...>, <hpa@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 3:08 pm

ok. I've picked up Cyrill's cleanup - can i add your acked-by line?


	Ingo

--
[view original message]
From: Sam Ravnborg <sam@...>
To: Ingo Molnar <mingo@...>
Cc: Cyrill Gorcunov <gorcunov@...>, <ak@...>, <tglx@...>, <hpa@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 3:26 pm

Yes - I should have been specific and not just said "looks good".

Acked-by: Sam Ravnborg <sam@ravnborg.org>


	Sam

--
[view original message]
From: Cyrill Gorcunov <gorcunov@...>
To: Sam Ravnborg <sam@...>
Cc: <ak@...>, <mingo@...>, <tglx@...>, <hpa@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 3:08 pm

[Sam Ravnborg - Sun, Feb 17, 2008 at 07:59:36PM +0100]

| On Sun, Feb 17, 2008 at 06:17:18PM +0300, Cyrill Gorcunov wrote:

| > Though we use PDA for regular task stack but that

| > is not acceptable for init_task wich is special

| > one. We still have to allocate init_task's stack

| > in that manner.

|

| hpa had some comments about this particular alignment.

| If we keep the alignmnet then Cyrill's patch looks good.

|

| But maybe we should check what is the real alignmment

| requirement (outside the scope of wha you do - someone

| more intiminate with this coide should do it).

|

| 	Sam

| 


Yes Sam, I've read Peter and Ingo comments on this patch

(actually I sent the same patch maybe week ago and Peter

and Ingo told me that we use %fs,%gs now for stack) but

as I pointed in comment - this alignment is still using

by Xen and lguest and even x86. So - it would be really

usefull for me if someone give me the last point - YES we

use such an alignment for stack, NO - we don't use it at all.

I was trying to hadle this myself - but I'm not a specialist

in this area you know ;)


		- Cyrill -

--
[view original message]
From: H. Peter Anvin <hpa@...>
To: Cyrill Gorcunov <gorcunov@...>
Cc: Sam Ravnborg <sam@...>, <ak@...>, <mingo@...>, <tglx@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 3:48 pm

It bugs me quite a bit that paravirt clients contain this hack

open-coded, but that's not *your* fault.  There probably should be a

macro to encapsulate the stack pointer location for a specific thread.


	-hpa

--
[view original message]
From: Cyrill Gorcunov <gorcunov@...>
To: H. Peter Anvin <hpa@...>
Cc: Sam Ravnborg <sam@...>, <ak@...>, <mingo@...>, <tglx@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 4:06 pm

Thanks Peter for comments. Peter could you clarify for me a bit

more on the string:


x86/kernel/head_32.S:339


	/* Set up the stack pointer */

	lss stack_start,%esp


but stack_start is defined as head_32.S:647


.data

ENTRY(stack_start)

	.long init_thread_union+THREAD_SIZE


so stack_start *must* be aligned with THREAD_SIZE in vmlinux.lds

at compiling time. There is no PDA at this booting time. Am I wrong?

If you're too busy - just reply me like "Read the code" ;)


		- Cyrill -

--
[view original message]
From: H. Peter Anvin <hpa@...>
To: Cyrill Gorcunov <gorcunov@...>
Cc: Sam Ravnborg <sam@...>, <ak@...>, <mingo@...>, <tglx@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 4:11 pm

That doesn't follow.


You're saying that it *must* be aligned, I don't think that's true

anymore; I think nowadays it's more accurate to say that it *is*

aligned, but I don't think that's fundamental.


	-hpa

--
[view original message]
From: Andi Kleen <ak@...>
To: H. Peter Anvin <hpa@...>
Cc: Cyrill Gorcunov <gorcunov@...>, Sam Ravnborg <sam@...>, <mingo@...>, <tglx@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of
Date: Monday, February 18, 2008 - 10:27 am

At least in .25 mainline current_thread_info() is still using

[re]sp arithmetic.  Also I think the stack backtracers also

rely on suitable alignment of the stack top. So right now it is still

fundamental. Now that could be all fixed by using segment

register references and might be, but so far that doesn't

seem to be finished yet.


-Andi

--
[view original message]
From: Cyrill Gorcunov <gorcunov@...>
To: H. Peter Anvin <hpa@...>
Cc: Sam Ravnborg <sam@...>, <ak@...>, <mingo@...>, <tglx@...>, <linux-kernel@...>
Subject: Re: [patch 2/2] x86: lds - Use THREAD_SIZE instead of numeric constant
Date: Sunday, February 17, 2008 - 4:15 pm

Thanks a lot, Peter.


		- Cyrill -

--
Previous thread: [patch 0/2] x86: vmlinux.lds cleanup by Cyrill Gorcunov on Sunday, February 17, 2008 - 11:17 am. (1 message)

Next thread: [patch 1/2] x86: lds - Use PAGE_SIZE instead of numeric constant by Cyrill Gorcunov on Sunday, February 17, 2008 - 11:17 am. (3 messages)