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authorKevin O'Connor <kevin@koconnor.net>2015-03-17 11:37:25 -0400
committerKevin O'Connor <kevin@koconnor.net>2015-03-18 01:46:56 -0400
commit251e26388b83f4bfd8a5ae28263db295e5b683b5 (patch)
tree0d4c0430771f91336580d1ed83510a8524d65597 /vgasrc
parent184496863a40ac1eff5612ba0da11399535bfa40 (diff)
downloadseabios-251e26388b83f4bfd8a5ae28263db295e5b683b5.tar.gz
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vgabios: Don't use extra stack if it appears a modern OS is in use
If the last mode set (while not in vm86 mode) was done from a VBE mode set call then disable the extra stack. This works under the premise that only a modern OS would invoke the VBE mode changing facilities and a modern OS would always call the vgabios with sufficient stack space. This is an ugly hack to work around a problem Windows Vista (and possibly later Windows releases) has with the VGA BIOS using a stack in the e-segment. Reported-by: Richard Laager <rlaager@wiktel.com> Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Diffstat (limited to 'vgasrc')
-rw-r--r--vgasrc/vgabios.c6
-rw-r--r--vgasrc/vgabios.h4
-rw-r--r--vgasrc/vgaentry.S18
3 files changed, 25 insertions, 3 deletions
diff --git a/vgasrc/vgabios.c b/vgasrc/vgabios.c
index 4aa50e1..7c1f0b8 100644
--- a/vgasrc/vgabios.c
+++ b/vgasrc/vgabios.c
@@ -304,6 +304,12 @@ vga_set_mode(int mode, int flags)
SET_BDA(video_mode, 0xff);
SET_BDA_EXT(vbe_mode, mode | (flags & MF_VBEFLAGS));
SET_BDA_EXT(vgamode_offset, (u32)vmode_g);
+ if (CONFIG_VGA_ALLOCATE_EXTRA_STACK && !(getcr0_vm86() & CR0_PE))
+ // Disable extra stack if it appears a modern OS is in use.
+ // This works around bugs in some versions of Windows (Vista
+ // and possibly later) when the stack is in the e-segment.
+ MASK_BDA_EXT(flags, BF_EXTRA_STACK
+ , (flags & MF_LEGACY) ? BF_EXTRA_STACK : 0);
if (memmodel == MM_TEXT) {
SET_BDA(video_cols, width);
SET_BDA(video_rows, height-1);
diff --git a/vgasrc/vgabios.h b/vgasrc/vgabios.h
index fd796f2..831f694 100644
--- a/vgasrc/vgabios.h
+++ b/vgasrc/vgabios.h
@@ -62,7 +62,8 @@ struct gfx_op {
#define GO_MEMSET 3
#define GO_MEMMOVE 4
-// Custom internal storage in BDA
+// Custom internal storage in BDA (don't change here without also
+// updating vgaentry.S)
#define VGA_CUSTOM_BDA 0xb9
struct vga_bda_s {
@@ -74,6 +75,7 @@ struct vga_bda_s {
#define BF_PM_MASK 0x0f
#define BF_EMULATE_TEXT 0x10
#define BF_SWCURSOR 0x20
+#define BF_EXTRA_STACK 0x40
#define GET_BDA_EXT(var) \
GET_FARVAR(SEG_BDA, ((struct vga_bda_s *)VGA_CUSTOM_BDA)->var)
diff --git a/vgasrc/vgaentry.S b/vgasrc/vgaentry.S
index f9cf656..e0ab954 100644
--- a/vgasrc/vgaentry.S
+++ b/vgasrc/vgaentry.S
@@ -104,14 +104,23 @@ entry_10:
ENTRY_ARG_VGA handle_10
iretw
+#define VGA_CUSTOM_BDA_FLAGS 0xb9
+#define BF_EXTRA_STACK 0x40
+
// Entry point using extra stack
DECLFUNC entry_10_extrastack
entry_10_extrastack:
cli
cld
- pushw %ds // Set %ds:%eax to space on ExtraStack
+ pushw %ds
pushl %eax
- movw %cs:ExtraStackSeg, %ds
+
+ movw $SEG_BDA, %ax // Check if extra stack is enabled
+ movw %ax, %ds
+ testb $BF_EXTRA_STACK, VGA_CUSTOM_BDA_FLAGS
+ jz 1f
+
+ movw %cs:ExtraStackSeg, %ds // Set %ds:%eax to space on ExtraStack
movl $(CONFIG_VGA_EXTRA_STACK_SIZE-PUSHBREGS_size-16), %eax
SAVEBREGS_POP_DSEAX // Save registers on extra stack
movl %esp, PUSHBREGS_size+8(%eax)
@@ -134,6 +143,11 @@ entry_10_extrastack:
RESTOREBREGS_DSEAX
iretw
+1: // Use regular entry point if the extra stack is disabled
+ popl %eax
+ popw %ds
+ jmp entry_10
+
// Timer irq handling
DECLFUNC entry_timer_hook
entry_timer_hook: