If a VBE mode set call is made, stop using the vgabios 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 <[email protected]> Signed-off-by: Kevin O'Connor <[email protected]> --- I ran some further tests with the Windows emulator crashing problem. I eventually came up with the targeted solution above. Basically, I tried to find a signature that indicates Windows is running and disable the extra stack in that case. It's a hack for sure, but it seems to work. For the curious, some other tests that I ran that didn't yield a solution: * The "concurrent dos" image I have actually uses vm86 mode and it still expects the vgabios to only use a tiny amount of stack space. So, just disabling the extra stack in vm86 mode breaks this "concurrent dos" image. * Windows faults on the first write access to the e-segment, so testing if the extra stack is read/writable doesn't work (as the test itself causes a fault which halts the emulation). * Windows actually copies the first 1 Meg before starting the emulation, so putting some kind of signature in the extra stack doesn't help detect if it's read-only. * When these troublesome vgabios calls are made, Windows is using a copy of the first 1 Meg instead of accessing it in place. If a log is written to the writable part of the first 1 Meg, then when the log is inspected later it doesn't show any of the troublesome calls. --- vgasrc/vbe.c | 1 + vgasrc/vgabios.h | 1 + vgasrc/vgainit.c | 15 +++++++++++++++ 3 files changed, 17 insertions(+) diff --git a/vgasrc/vbe.c b/vgasrc/vbe.c index af3d0cc..834d7b3 100644 --- a/vgasrc/vbe.c +++ b/vgasrc/vbe.c @@ -205,6 +205,7 @@ static void vbe_104f02(struct bregs *regs) { dprintf(1, "VBE mode set: %x\n", regs->bx); + check_extra_stack(); int mode = regs->bx & ~MF_VBEFLAGS; int flags = regs->bx & MF_VBEFLAGS; diff --git a/vgasrc/vgabios.h b/vgasrc/vgabios.h index fd796f2..985bbbb 100644 --- a/vgasrc/vgabios.h +++ b/vgasrc/vgabios.h @@ -100,6 +100,7 @@ extern u8 vgafont16alt[]; // vgainit.c extern struct video_save_pointer_s video_save_pointer_table; extern struct video_param_s video_param_table[29]; +void check_extra_stack(void); // vgabios.c extern int VgaBDF; diff --git a/vgasrc/vgainit.c b/vgasrc/vgainit.c index 8d12261..4616883 100644 --- a/vgasrc/vgainit.c +++ b/vgasrc/vgainit.c @@ -86,6 +86,21 @@ allocate_extra_stack(void) } } +void +check_extra_stack(void) +{ + if (!CONFIG_VGA_ALLOCATE_EXTRA_STACK) + return; + extern void entry_10(void); + if (GET_IVT(0x10).offset == (u32)entry_10) + return; + // Disable the extra stack if a VBE mode set call is made. This + // works around a bug in Windows Vista when the stack is in the + // e-segment. + dprintf(1, "Disabling SeaVGABIOS extra stack.\n"); + SET_IVT(0x10, SEGOFF(get_global_seg(), (u32)entry_10)); +} + /**************************************************************** * Timer hook -- 1.9.3 _______________________________________________ SeaBIOS mailing list [email protected] http://www.seabios.org/mailman/listinfo/seabios
