Index: sys/boot/efi/loader/arch/amd64/framebuffer.c
===================================================================
--- sys/boot/efi/loader/arch/amd64/framebuffer.c	(revision 287317)
+++ sys/boot/efi/loader/arch/amd64/framebuffer.c	(working copy)
@@ -43,6 +43,21 @@
 static EFI_GUID pciio_guid = EFI_PCI_IO_PROTOCOL_GUID;
 static EFI_GUID uga_guid = EFI_UGA_DRAW_PROTOCOL_GUID;
 
+static u_int
+efifb_color_depth(struct efi_fb *efifb)
+{
+	uint32_t mask;
+	u_int depth;
+
+	mask = efifb->fb_mask_red | efifb->fb_mask_green |
+	    efifb->fb_mask_blue | efifb->fb_mask_reserved;
+	if (mask == 0)
+		return (0);
+	for (depth = 1; mask != 1; depth++)
+		mask >>= 1;
+	return (depth);
+}
+
 static int
 efifb_mask_from_pixfmt(struct efi_fb *efifb, EFI_GRAPHICS_PIXEL_FORMAT pixfmt,
     EFI_PIXEL_BITMASK *pixinfo)
@@ -95,6 +110,7 @@
 static int
 efifb_from_uga(struct efi_fb *efifb, EFI_UGA_DRAW_PROTOCOL *uga)
 {
+	EFI_UGA_PIXEL pix0, pix1;
 	uint8_t *buf;
 	EFI_PCI_IO_PROTOCOL *pciio;
 	EFI_HANDLE handle;
@@ -102,7 +118,8 @@
 	UINTN bufofs, bufsz;
 	uint64_t address, length;
 	uint32_t horiz, vert, depth, refresh;
-	u_int bar;
+	uint32_t raw0, raw1;
+	u_int bar, bpp, fbbar;
 
 	status = uga->GetMode(uga, &horiz, &vert, &depth, &refresh);
         if (EFI_ERROR(status))
@@ -138,6 +155,7 @@
 	/* Attempt to get the frame buffer address (imprecise). */
 	efifb->fb_addr = 0;
 	efifb->fb_size = 0;
+	fbbar = -1;
 	for (bar = 0; bar < 6; bar++) {
 		status = pciio->GetBarAttributes(pciio, bar, NULL,
 		    (EFI_HANDLE *)&buf);
@@ -163,12 +181,34 @@
 		if (length > efifb->fb_size) {
 			efifb->fb_addr = address;
 			efifb->fb_size = length;
+			fbbar = bar;
 		}
 	}
 	if (efifb->fb_addr == 0 || efifb->fb_size == 0)
 		return (1);
-	/* TODO determine the stride. */
-	efifb->fb_stride = efifb->fb_width;	/* XXX */
+	/*
+	 * Determine the stride by changing the frame buffer, starting at
+	 * the offset in the frame buffer that corresponds to the width,
+	 * and checking if the first pixel on the second scan line changed.
+	 */
+	uga->Blt(uga, &pix0, EfiUgaVideoToBltBuffer, 0, 1, 0, 0, 1, 1, 0);
+	bpp = (efifb_color_depth(efifb) + 7) >> 3;
+	efifb->fb_stride = efifb->fb_width;
+	while (1) {
+		address = efifb->fb_stride * bpp;
+		pciio->Mem.Read(pciio, EfiPciIoWidthUint32, fbbar, address,
+		    1, &raw0);
+		raw1 = ~raw0;
+		pciio->Mem.Write(pciio, EfiPciIoWidthUint32, fbbar, address,
+		    1, &raw1);
+		uga->Blt(uga, &pix1, EfiUgaVideoToBltBuffer, 0, 1, 0, 0,
+		    1, 1, 0);
+		pciio->Mem.Write(pciio, EfiPciIoWidthUint32, fbbar, address,
+		    1, &raw0);
+		if (memcmp(&pix0, &pix1, sizeof(EFI_UGA_PIXEL)))
+			break;
+		efifb->fb_stride++;
+	}
 	return (0);
 }
 
@@ -193,18 +233,11 @@
 static void
 print_efifb(int mode, struct efi_fb *efifb, int verbose)
 {
-	uint32_t mask;
 	u_int depth;
 
 	if (mode >= 0)
 		printf("mode %d: ", mode);
-	mask = efifb->fb_mask_red | efifb->fb_mask_green |
-	    efifb->fb_mask_blue | efifb->fb_mask_reserved;
-	if (mask > 0) {
-		for (depth = 1; mask != 1; depth++)
-			mask >>= 1;
-	} else
-		depth = 0;
+	depth = efifb_color_depth(efifb);
 	printf("%ux%ux%u, stride=%u", efifb->fb_width, efifb->fb_height,
 	    depth, efifb->fb_stride);
 	if (verbose) {