x86 setup: fix asm constraints in vesa_store_edid

Impact: fix potential miscompile (currently believed non-manifest)

As the comment explains, the VBE DDC call can clobber any register.
Tell the compiler about that fact.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 6 deletions

diff --git a/arch/x86/boot/video-vesa.c b/arch/x86/boot/video-vesa.c
index 75115849af33..4a58c8ce3f69 100644
--- a/arch/x86/boot/video-vesa.c
+++ b/arch/x86/boot/video-vesa.c
@@ -269,9 +269,8 @@ void vesa_store_edid(void)
            we genuinely have to assume all registers are destroyed here. */
 
         asm("pushw %%es; movw %2,%%es; "INT10"; popw %%es"
-            : "+a" (ax), "+b" (bx)
-            :  "c" (cx), "D" (di)
-            : "esi");
+            : "+a" (ax), "+b" (bx), "+c" (cx), "+D" (di)
+            : : "esi", "edx");
 
         if (ax != 0x004f)
                 return;         /* No EDID */
@@ -285,9 +284,9 @@ void vesa_store_edid(void)
         dx = 0;                 /* EDID block number */
         di =(size_t) &boot_params.edid_info; /* (ES:)Pointer to block */
         asm(INT10
-            : "+a" (ax), "+b" (bx), "+d" (dx), "=m" (boot_params.edid_info)
-            : "c" (cx), "D" (di)
-            : "esi");
+            : "+a" (ax), "+b" (bx), "+d" (dx), "=m" (boot_params.edid_info),
+              "+c" (cx), "+D" (di)
+            : : "esi");
 #endif /* CONFIG_FIRMWARE_EDID */
 }