1 files changed, 29 insertions, 10 deletions

diff --git a/arch/i386/boot/memory.c b/arch/i386/boot/memory.c
index 1a2e62db8bed..378353956b5d 100644
--- a/arch/i386/boot/memory.c
+++ b/arch/i386/boot/memory.c
@@ -20,6 +20,7 @@
 
 static int detect_memory_e820(void)
 {
+        int count = 0;
         u32 next = 0;
         u32 size, id;
         u8 err;
@@ -27,20 +28,33 @@ 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
+                   screwed up the map at that point, we might have a
+                   partial map, the full map, or complete garbage, so
+                   just return failure. */
+                if (id != SMAP) {
+                        count = 0;
+                        break;
+                }
 
-                if (err || id != SMAP)
+                if (err)
                         break;
 
-                boot_params.e820_entries++;
+                count++;
                 desc++;
-        } while (next && boot_params.e820_entries < E820MAX);
+        } while (next && count < E820MAX);
 
-        return boot_params.e820_entries;
+        return boot_params.e820_entries = count;
 }
 
 static int detect_memory_e801(void)
@@ -89,11 +103,16 @@ static int detect_memory_88(void)
 
 int detect_memory(void)
 {
+        int err = -1;
+
         if (detect_memory_e820() > 0)
-                return 0;
+                err = 0;
 
         if (!detect_memory_e801())
-                return 0;
+                err = 0;
+
+        if (!detect_memory_88())
+                err = 0;
 
-        return detect_memory_88();
+        return err;
 }