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x86emu: fix jump_near_IMM to handle DATA: flag correctly 

Before (data flag ignored -> broken):
66                  DATA:
e944f1              JMP       1ff6

After (fixed):
66                  DATA:
e944f1ffff          JMP       00001ff8

This subtle difference in the length of decoded instruction meant
that the VBE call jumped to the routine setting AX=0x14F (VBE Failed)
instead of the routine that set AX=0x4F (VBE success).

The ability to run the same code in vm86 significantly aided the
debugging of this issue. Those X.org developers who would like to drop
vm86 better take special care towards _all_ vesa bugs, as those will
expose further issues.

Imported from:
http://cgit.freedesktop.org/xorg/xserver/commit/hw/xfree86/x86emu?id=cc2c73ddcb4370a7c3ad439cda4da825156c26c9
Signed-off-by: Stefan Reinauer <reinauer@google.com>

Change-Id: Id08ead9b17468cf19ede45508e5dcc50e45b5acf
Signed-off-by: Luc Verhaegen <libv@skynet.be>
Tested-by: Luc Verhaegen <libv@skynet.be>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-on: http://review.coreboot.org/1365
Tested-by: build bot (Jenkins)
Reviewed-by: Anton Kochkov <anton.kochkov@gmail.com>
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
This commit is contained in:
Stefan Reinauer 2012-07-26 15:48:17 -07:00 committed by Patrick Georgi
parent 3b69578cd2
commit 170d19c2ad
1 changed files with 16 additions and 7 deletions
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13
src/devices/oprom/x86emu/ops.c
View File

@ -4301,16 +4301,25 @@ Handles opcode 0xe9
****************************************************************************/
static void x86emuOp_jump_near_IMM(u8 X86EMU_UNUSED(op1))
{
int ip;
u32 ip;
START_OF_INSTR();
DECODE_PRINTF("JMP\t");
if (M.x86.mode & SYSMODE_PREFIX_DATA) {
ip = (u32)fetch_long_imm();
ip += (u32)M.x86.R_EIP;
DECODE_PRINTF2("%08x\n", (u32)ip);
JMP_TRACE(M.x86.saved_cs, M.x86.saved_ip, M.x86.R_CS, ip, " NEAR ");
TRACE_AND_STEP();
M.x86.R_EIP = (u32)ip;
} else {
ip = (s16)fetch_word_imm();
ip += (s16)M.x86.R_IP;
DECODE_PRINTF2("%04x\n", ip);
DECODE_PRINTF2("%04x\n", (u16)ip);
JMP_TRACE(M.x86.saved_cs, M.x86.saved_ip, M.x86.R_CS, ip, " NEAR ");
TRACE_AND_STEP();
M.x86.R_IP = (u16)ip;
}
DECODE_CLEAR_SEGOVR();
END_OF_INSTR();
}