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From: Kevin O'Connor <kevin@koconnor.net>
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Date: Wed Feb 5 22:47:29 2014 -0500
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Subject: vgabios: Attempt to detect old x86emu and force a fault.
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Upstream-Commit: 8032b8a0fec550de5cb2f7d37aa031cebc2200c3
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Bug-Debian: http://bugs.debian.org/737142
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Check for cases where the leal instruction does not work. This
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instruction is known to not be emulated properly on old versions of
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x86emu. If a broken version of x86emu is found, force a fault that
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x86emu will easily detect. This should help prevent soft failures
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when running old software.
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Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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diff --git a/vgasrc/vgaentry.S b/vgasrc/vgaentry.S
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index 9854448..6e31c4e 100644
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--- a/vgasrc/vgaentry.S
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+++ b/vgasrc/vgaentry.S
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@@ -45,9 +45,26 @@ _rom_header_signature:
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* Entry points
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****************************************************************/
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- // This macro is the same as ENTRY_ARG except the "calll"
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- // instruction is avoided to work around known issues in the
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- // emulation of some versions of x86emu.
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+ // Force a fault if found to be running on broken x86emu versions.
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+ DECLFUNC x86emu_fault
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+x86emu_fault:
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+1: hlt
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+ jmp 1b
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+
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+ // This macro implements a call while avoiding instructions
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+ // that old versions of x86emu have problems with.
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+ .macro VGA_CALLL cfunc
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+ // Make sure leal instruction works.
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+ movl $0x8000, %ecx
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+ leal (%ecx, %ecx, 1), %ecx
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+ cmpl $0x10000, %ecx
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+ jne x86emu_fault
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+ // Use callw instead of calll
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+ push %ax
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+ callw \cfunc
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+ .endm
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+
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+ // This macro is the same as ENTRY_ARG except VGA_CALLL is used.
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.macro ENTRY_ARG_VGA cfunc
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cli
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cld
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@@ -57,7 +74,7 @@ _rom_header_signature:
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movl %esp, %ebx // Backup %esp, then zero high bits
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movzwl %sp, %esp
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movl %esp, %eax // First arg is pointer to struct bregs
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- pushw %ax ; callw \cfunc
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+ VGA_CALLL \cfunc
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movl %ebx, %esp // Restore %esp (including high bits)
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POPBREGS
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.endm
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@@ -103,7 +120,7 @@ entry_10_extrastack:
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movw %ds, %dx // Setup %ss/%esp and call function
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movw %dx, %ss
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movl %eax, %esp
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- pushw %ax ; callw handle_10
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+ VGA_CALLL handle_10
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movl %esp, %eax // Restore registers and return
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movw BREGS_size+4(%eax), %ss
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