linux-kernel - Re: [bisected] Re: [PATCH 05 of 12] xen: add p2m mfn_list

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Message-ID: <20080528141012.GA4669@uranus.ravnborg.org>
Date:	Wed, 28 May 2008 16:10:12 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>, x86@...nel.org
Subject: Re: [bisected] Re: [PATCH 05 of 12] xen: add p2m mfn_list_list

On Wed, May 28, 2008 at 03:02:14PM +0100, Jeremy Fitzhardinge wrote:
> 
> The use of __section(.data.page_aligned) (or worse 
> __attribute__((section(".data.page_aligned"))) is fairly verbose and 
> brittle. I've got a (totally untested) proposed patch below, to 
> introduce __page_aligned_data|bss which sets the section and the 
> alignment. This will work, but it requires that all page-aligned 
> variables also have an alignment associated with them, so that mis-sized 
> ones don't push the others around.
> 
> There aren't very many users of .data|bss.page_aligned, so it should be 
> easy enough to fix them all up.
> 
> A link-time warning would be good too, of course.

I cooked up this:
diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
index ce5ed08..963b2ae 100644
--- a/arch/x86/kernel/vmlinux_32.lds.S
+++ b/arch/x86/kernel/vmlinux_32.lds.S
@@ -40,6 +40,7 @@ SECTIONS
   .text : AT(ADDR(.text) - LOAD_OFFSET) {
        . = ALIGN(PAGE_SIZE); /* not really needed, already page aligned */
        *(.text.page_aligned)
+       end_text_page_aligned = .;
        TEXT_TEXT
        SCHED_TEXT
        LOCK_TEXT
@@ -49,6 +50,9 @@ SECTIONS
        _etext = .;                     /* End of text section */
   } :text = 0x9090

+       ASSERT((end_text_page_aligned == ALIGN((end_text_page_aligned), PAGE_SIZE)),
+              "Text in .text.page_aligned are not modulo PAGE_SIZE")
+
   . = ALIGN(16);               /* Exception table */
   __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
        __start___ex_table = .;
@@ -89,6 +93,8 @@ SECTIONS
        *(.data.page_aligned)
        *(.data.idt)
   }
+       ASSERT((. == ALIGN(PAGE_SIZE)),
+              "Data in .data.page_aligned are not modulo PAGE_SIZE")

   . = ALIGN(32);
   .data.cacheline_aligned : AT(ADDR(.data.cacheline_aligned) - LOAD_OFFSET) {


But we should try to do it so all archs can benefit.
And it failed in the second ASSERT - I dunno why.

Soccer duties - so I have to run.

	Sam
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