From 4ee5b10abeb2b5581be10d3022694cd19084e9b0 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Thu, 27 Sep 2007 17:17:12 -0700
Subject: [PATCH] [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@zytor.com>
---
arch/i386/boot/memory.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/i386/boot/memory.c b/arch/i386/boot/memory.c
index bccaa1cf6645..378353956b5d 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
--
2.20.1