linux-kernel - [GIT PULL] Correct the SMAP check in the e820 probe (fixed)

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Message-Id: <200709281753.l8SHrwRe019689@tazenda.hos.anvin.org>
Date:	Fri, 28 Sep 2007 10:53:58 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	jkeating@...hat.com, cebbert@...hat.com, jordan.crouse@....com,
	pommnitz@...oo.com
Subject: [GIT PULL] Correct the SMAP check in the e820 probe (fixed)

Hi Linus,

Please pull:

  git://git.kernel.org/pub/scm/linux/kernel/git/hpa/linux-2.6-x86setup.git for-linus

Thanks for catching the obvious thinko.

H. Peter Anvin (1):
      [x86 setup] Correct the SMAP check for INT 0x15, AX=0xe820

 arch/i386/boot/memory.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

[Log messages and full diffs follow]

commit 4ee5b10abeb2b5581be10d3022694cd19084e9b0
Author: H. Peter Anvin <hpa@...or.com>
Date:   Thu Sep 27 17:17:12 2007 -0700

    [x86 setup] Correct the SMAP check for INT 0x15, AX=0xe820
    
    The e820 probe code was checking %edx, not %eax, for the SMAP
    signature on return.  This worked on *almost* all systems, since %edx
    still contained SMAP from the call on entry, but on a handful of
    systems it failed -- plus, we would have missed real mismatches.
    
    The error output is "=d" to make sure gcc knows %edx is clobbered
    here.
    
    Signed-off-by: H. Peter Anvin <hpa@...or.com>

diff --git a/arch/i386/boot/memory.c b/arch/i386/boot/memory.c
index bccaa1c..3783539 100644
--- a/arch/i386/boot/memory.c
+++ b/arch/i386/boot/memory.c
@@ -28,11 +28,14 @@ static int detect_memory_e820(void)
 
 	do {
 		size = sizeof(struct e820entry);
-		id = SMAP;
+
+		/* Important: %edx is clobbered by some BIOSes,
+		   so it must be either used for the error output
+		   or explicitly marked clobbered. */
 		asm("int $0x15; setc %0"
-		    : "=am" (err), "+b" (next), "+d" (id), "+c" (size),
+		    : "=d" (err), "+b" (next), "=a" (id), "+c" (size),
 		      "=m" (*desc)
-		    : "D" (desc), "a" (0xe820));
+		    : "D" (desc), "d" (SMAP), "a" (0xe820));
 
 		/* Some BIOSes stop returning SMAP in the middle of
 		   the search loop.  We don't know exactly how the BIOS
-
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