[SeaBIOS] [PATCH 8/8] SeaVGABios/cbvga: Add crash detection handler

[Patrick Rudolph]

Add a crash detection handler to detect a crash on mode
change and don't clear the screen on mode change ever again.

This is a workaround for Microsoft Windows doing some magic
to the INT 15 handler, preventing memcpy_high to function properly.

Allows Microsoft's Windows 7 to boot in safe mode.
Some artifacts might stay in the unused part of the framebuffer,
but at least it is possible to use all advertised VESA modes.

Signed-off-by: Patrick Rudolph <siro at das-labor.org>

diff --git a/vgasrc/cbvga.c b/vgasrc/cbvga.c
index bc5b79e..af4b138 100644
--- a/vgasrc/cbvga.c
+++ b/vgasrc/cbvga.c
@@ -195,6 +195,8 @@ cbvga_save_restore(int cmd, u16 seg, void *data)
     return bda_save_restore(cmd, seg, data);
 }
 
+static u16 crash_detect VAR16;
+
 int
 cbvga_set_mode(struct vgamode_s *vmode_g, int flags)
 {
@@ -210,6 +212,18 @@ cbvga_set_mode(struct vgamode_s *vmode_g, int flags)
             memset16_far(SEG_CTEXT, (void*)0, 0x0720, 80*25*2);
             return 0;
         }
+        /* Windows replaced INT 15h handler, resulting in a crash, as
+         * mempcpy_high doesn't work any more.
+         * We can't do anything about that, but try to detect the crash
+         * and don't clear the screen.
+         */
+        if (GET_GLOBAL(crash_detect) == 0xdead) {
+            dprintf(1, "Detected crash, skipping clear screen.\n");
+            return 0;
+        }
+        /* Install crash signal */
+        SET_VGA(crash_detect, 0xdead);
+
         struct gfx_op op;
         init_gfx_op(&op, &CBmodeinfo);
         op.x = op.y = 0;
@@ -217,6 +231,9 @@ cbvga_set_mode(struct vgamode_s *vmode_g, int flags)
         op.ylen = GET_GLOBAL(CBmodeinfo.height);
         op.op = GO_MEMSET;
         handle_gfx_op(&op);
+
+        /* Reset crash signal */
+        SET_VGA(crash_detect, 0);
     }
     return 0;
 }
-- 
2.9.3