linux-kernel - [PATCH] mark %esi as clobbered in E820 BIOS call

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Date:	Fri, 27 Mar 2009 13:14:41 -0400
From:	"Michael K. Johnson" <johnsonm@...th.com>
To:	jmforbes@...uxtx.org, hpa@...or.com
Cc:	Jordan_Hargrave@...l.com, linux-kernel@...r.kernel.org
Subject: [PATCH] mark %esi as clobbered in E820 BIOS call

Justin and Peter, please review this for stable .y trees.  Peter,
please review this for trunk unless you decide to do a more 
extensive workaround for BIOS register clobbering.

Thanks!

$ cat e820-esi-clobber-workaround.patch
Jordan Hargrave diagnosed a BIOS clobbering %esi in the E820 call.
That particular BIOS has been fixed, but there is a possibility that
this is responsible for other occasional reports of early boot
failure, and it does not hurt to add %esi to the clobbers.

Cc: H. Peter Anvin <hpa@...or.com>
Cc: Justin Forbes <jmforbes@...uxtx.org>

Signed-off-by: Michael K Johnson <johnsonm@...th.com>

diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index 8c3c25f..fa85af7 100644
--- a/arch/x86/boot/memory.c
+++ b/arch/x86/boot/memory.c
@@ -27,13 +27,14 @@ static int detect_memory_e820(void)
 	do {
 		size = sizeof(struct e820entry);

-		/* Important: %edx is clobbered by some BIOSes,
-		   so it must be either used for the error output
+		/* Important: %edx and %esi are clobbered by some BIOSes,
+		   so they must be either used for the error output
 		   or explicitly marked clobbered. */
 		asm("int $0x15; setc %0"
 		    : "=d" (err), "+b" (next), "=a" (id), "+c" (size),
 		      "=m" (*desc)
-		    : "D" (desc), "d" (SMAP), "a" (0xe820));
+		    : "D" (desc), "d" (SMAP), "a" (0xe820)
+		    : "%esi");

 		/* BIOSes which terminate the chain with CF = 1 as opposed
 		   to %ebx = 0 don't always report the SMAP signature on
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