[x86 setup] Don't rely on the VESA BIOS being register-clean

The VESA BIOS is specified to be register-clean.  However, we have now
found at least one system which violates that.  Thus, be as paranoid
about VESA calls as about everything else.

Huge thanks to Will Simoneau for reporting, diagnosing, and testing
this out on Dell Inspiron 5150.

Cc: Will Simoneau <simoneau@ele.uri.edu>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/i386/boot/video-vesa.c

@@ -29,7 +29,7 @@ static void vesa_store_mode_params_graphics(void);
 static int vesa_probe(void)
 {
 #if defined(CONFIG_VIDEO_VESA) || defined(CONFIG_FIRMWARE_EDID)
-	u16 ax;
+	u16 ax, cx, di;
 	u16 mode;
 	addr_t mode_ptr;
 	struct mode_info *mi;
@@ -39,9 +39,11 @@ static int vesa_probe(void)
 
 	vginfo.signature = VBE2_MAGIC;
 
-	/* Optimistically assume a VESA BIOS is register-clean... */
 	ax = 0x4f00;
-	asm("int $0x10" : "+a" (ax), "=m" (vginfo) : "D" (&vginfo));
+	di = (size_t)&vginfo;
+	asm(INT10
+	    : "+a" (ax), "+D" (di), "=m" (vginfo)
+	    : : "ebx", "ecx", "edx", "esi");
 
 	if (ax != 0x004f ||
 	    vginfo.signature != VESA_MAGIC ||
@@ -64,9 +66,11 @@ static int vesa_probe(void)
 		memset(&vminfo, 0, sizeof vminfo); /* Just in case... */
 
 		ax = 0x4f01;
-		asm("int $0x10"
-		    : "+a" (ax), "=m" (vminfo)
-		    : "c" (mode), "D" (&vminfo));
+		cx = mode;
+		di = (size_t)&vminfo;
+		asm(INT10
+		    : "+a" (ax), "+c" (cx), "+D" (di), "=m" (vminfo)
+		    : : "ebx", "edx", "esi");
 
 		if (ax != 0x004f)
 			continue;
@@ -102,16 +106,18 @@ static int vesa_probe(void)
 
 static int vesa_set_mode(struct mode_info *mode)
 {
-	u16 ax;
+	u16 ax, bx, cx, di;
 	int is_graphic;
 	u16 vesa_mode = mode->mode - VIDEO_FIRST_VESA;
 
 	memset(&vminfo, 0, sizeof vminfo); /* Just in case... */
 
 	ax = 0x4f01;
-	asm("int $0x10"
-	    : "+a" (ax), "=m" (vminfo)
-	    : "c" (vesa_mode), "D" (&vminfo));
+	cx = vesa_mode;
+	di = (size_t)&vminfo;
+	asm(INT10
+	    : "+a" (ax), "+c" (cx), "+D" (di), "=m" (vminfo)
+	    : : "ebx", "edx", "esi");
 
 	if (ax != 0x004f)
 		return -1;
@@ -129,9 +135,11 @@ static int vesa_set_mode(struct mode_info *mode)
 
 
 	ax = 0x4f02;
-	asm volatile("int $0x10"
-		     : "+a" (ax)
-		     : "b" (vesa_mode), "D" (0));
+	bx = vesa_mode;
+	di = 0;
+	asm volatile(INT10
+		     : "+a" (ax), "+b" (bx), "+D" (di)
+		     : : "ecx", "edx", "esi");
 
 	if (ax != 0x004f)
 		return -1;