[PATCH v3] x86emu: Correctly handle 0x66 prefix for some instructions
I repost this patch because I havn't got any replies from maintainers since I posted the initial patch back in March. Some instructions are not emulated correctly by x86emu when they are prefixed by the 0x66 opcode. I've identified problems in the emulation of these intructions: ret, enter, leave, iret and some forms of call. Most of the time, the problem is that these instructions should push or pop 32-bit values to/from the stack, instead of 16bit, when they are prefixed by the 0x66 special opcode. The SeaBIOS project aims to produce a complete legacy BIOS implementation as well as a VGA option ROM, entirely written in C and using the GCC compiler. In 16bit code produced by the GCC compiler, the 0x66 prefix is used almost everywhere. This patch is necessary to allow the SeaBIOS VGA option ROM to function with Xorg when using the vesa driver. SeaBIOS currently use postprocessing on the ROM assembly output to replace the affected instruction with alternative unaffected instructions. This is obviously not very elegant, and this fix in x86emu would be more appropriate. v2: - Decrement BP instead of EBP in accordance with the Intel Manual - Assign EIP instead of IP when poping the return address from the stack in 32-bit operand size mode in ret_far_IMM, ret_far, and iret - When poping EFLAGS from the stack in iret in 32-bit operand size mode, apply some mask to preserve Read-only flags. v3: - Rebase Signed-off-by: Julian Pidancet <julian.pidancet@gmail.com> --- hw/xfree86/x86emu/ops.c | 192 ++++++++++++++++++++++++++++++++++------------ 1 files changed, 142 insertions(+), 50 deletions(-) diff --git a/hw/xfree86/x86emu/ops.c b/hw/xfree86/x86emu/ops.c index 76b8358..d4a4caf 100644 --- a/hw/xfree86/x86emu/ops.c +++ b/hw/xfree86/x86emu/ops.c @@ -8949,7 +8949,11 @@ x86emuOp_ret_near_IMM(u8 X86EMU_UNUSED(op1)) DECODE_PRINTF2("%x\n", imm); RETURN_TRACE("RET", M.x86.saved_cs, M.x86.saved_ip); TRACE_AND_STEP(); - M.x86.R_IP = pop_word(); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_EIP = pop_long(); + } else { + M.x86.R_IP = pop_word(); + } M.x86.R_SP += imm; DECODE_CLEAR_SEGOVR(); END_OF_INSTR(); @@ -8966,7 +8970,11 @@ x86emuOp_ret_near(u8 X86EMU_UNUSED(op1)) DECODE_PRINTF("RET\n"); RETURN_TRACE("RET", M.x86.saved_cs, M.x86.saved_ip); TRACE_AND_STEP(); - M.x86.R_IP = pop_word(); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_EIP = pop_long(); + } else { + M.x86.R_IP = pop_word(); + } DECODE_CLEAR_SEGOVR(); END_OF_INSTR(); } @@ -9259,8 +9267,13 @@ x86emuOp_enter(u8 X86EMU_UNUSED(op1)) frame_pointer = M.x86.R_SP; if (nesting > 0) { for (i = 1; i < nesting; i++) { - M.x86.R_BP -= 2; - push_word(fetch_data_word_abs(M.x86.R_SS, M.x86.R_BP)); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_BP -= 4; + push_long(fetch_data_long_abs(M.x86.R_SS, M.x86.R_BP)); + } else { + M.x86.R_BP -= 2; + push_word(fetch_data_word_abs(M.x86.R_SS, M.x86.R_BP)); + } } push_word(frame_pointer); } @@ -9281,7 +9294,11 @@ x86emuOp_leave(u8 X86EMU_UNUSED(op1)) DECODE_PRINTF("LEAVE\n"); TRACE_AND_STEP(); M.x86.R_SP = M.x86.R_BP; - M.x86.R_BP = pop_word(); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_EBP = pop_long(); + } else { + M.x86.R_BP = pop_word(); + } DECODE_CLEAR_SEGOVR(); END_OF_INSTR(); } @@ -9301,8 +9318,13 @@ x86emuOp_ret_far_IMM(u8 X86EMU_UNUSED(op1)) DECODE_PRINTF2("%x\n", imm); RETURN_TRACE("RETF", M.x86.saved_cs, M.x86.saved_ip); TRACE_AND_STEP(); - M.x86.R_IP = pop_word(); - M.x86.R_CS = pop_word(); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_EIP = pop_long(); + M.x86.R_CS = pop_long() & 0xffff; + } else { + M.x86.R_IP = pop_word(); + M.x86.R_CS = pop_word(); + } M.x86.R_SP += imm; DECODE_CLEAR_SEGOVR(); END_OF_INSTR(); @@ -9319,8 +9341,13 @@ x86emuOp_ret_far(u8 X86EMU_UNUSED(op1)) DECODE_PRINTF("RETF\n"); RETURN_TRACE("RETF", M.x86.saved_cs, M.x86.saved_ip); TRACE_AND_STEP(); - M.x86.R_IP = pop_word(); - M.x86.R_CS = pop_word(); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_EIP = pop_long(); + M.x86.R_CS = pop_long() & 0xffff; + } else { + M.x86.R_IP = pop_word(); + M.x86.R_CS = pop_word(); + } DECODE_CLEAR_SEGOVR(); END_OF_INSTR(); } @@ -9421,9 +9448,15 @@ x86emuOp_iret(u8 X86EMU_UNUSED(op1)) TRACE_AND_STEP(); - M.x86.R_IP = pop_word(); - M.x86.R_CS = pop_word(); - M.x86.R_FLG = pop_word(); + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + M.x86.R_EIP = pop_long(); + M.x86.R_CS = pop_long() & 0xffff; + M.x86.R_EFLG = (pop_long() & 0x257FD5) | (M.x86.R_EFLG & 0x1A0000); + } else { + M.x86.R_IP = pop_word(); + M.x86.R_CS = pop_word(); + M.x86.R_FLG = pop_word(); + } DECODE_CLEAR_SEGOVR(); END_OF_INSTR(); } @@ -11740,19 +11773,36 @@ x86emuOp_opcFF_word_RM(u8 X86EMU_UNUSED(op1)) } break; case 2: /* call word ptr ... */ - destval = fetch_data_word(destoffset); - TRACE_AND_STEP(); - push_word(M.x86.R_IP); - M.x86.R_IP = destval; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destval = fetch_data_long(destoffset); + TRACE_AND_STEP(); + push_long(M.x86.R_EIP); + M.x86.R_EIP = destval; + } else { + destval = fetch_data_word(destoffset); + TRACE_AND_STEP(); + push_word(M.x86.R_IP); + M.x86.R_IP = destval; + } break; case 3: /* call far ptr ... */ - destval = fetch_data_word(destoffset); - destval2 = fetch_data_word(destoffset + 2); - TRACE_AND_STEP(); - push_word(M.x86.R_CS); - M.x86.R_CS = destval2; - push_word(M.x86.R_IP); - M.x86.R_IP = destval; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destval = fetch_data_long(destoffset); + destval2 = fetch_data_word(destoffset + 4); + TRACE_AND_STEP(); + push_long(M.x86.R_CS); + M.x86.R_CS = destval2; + push_long(M.x86.R_EIP); + M.x86.R_EIP = destval; + } else { + destval = fetch_data_word(destoffset); + destval2 = fetch_data_word(destoffset + 2); + TRACE_AND_STEP(); + push_word(M.x86.R_CS); + M.x86.R_CS = destval2; + push_word(M.x86.R_IP); + M.x86.R_IP = destval; + } break; case 4: /* jmp word ptr ... */ destval = fetch_data_word(destoffset); @@ -11825,19 +11875,36 @@ x86emuOp_opcFF_word_RM(u8 X86EMU_UNUSED(op1)) } break; case 2: /* call word ptr ... */ - destval = fetch_data_word(destoffset); - TRACE_AND_STEP(); - push_word(M.x86.R_IP); - M.x86.R_IP = destval; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destval = fetch_data_long(destoffset); + TRACE_AND_STEP(); + push_long(M.x86.R_EIP); + M.x86.R_EIP = destval; + } else { + destval = fetch_data_word(destoffset); + TRACE_AND_STEP(); + push_word(M.x86.R_IP); + M.x86.R_IP = destval; + } break; case 3: /* call far ptr ... */ - destval = fetch_data_word(destoffset); - destval2 = fetch_data_word(destoffset + 2); - TRACE_AND_STEP(); - push_word(M.x86.R_CS); - M.x86.R_CS = destval2; - push_word(M.x86.R_IP); - M.x86.R_IP = destval; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destval = fetch_data_long(destoffset); + destval2 = fetch_data_word(destoffset + 4); + TRACE_AND_STEP(); + push_long(M.x86.R_CS); + M.x86.R_CS = destval2; + push_long(M.x86.R_EIP); + M.x86.R_EIP = destval; + } else { + destval = fetch_data_word(destoffset); + destval2 = fetch_data_word(destoffset + 2); + TRACE_AND_STEP(); + push_word(M.x86.R_CS); + M.x86.R_CS = destval2; + push_word(M.x86.R_IP); + M.x86.R_IP = destval; + } break; case 4: /* jmp word ptr ... */ destval = fetch_data_word(destoffset); @@ -11910,19 +11977,36 @@ x86emuOp_opcFF_word_RM(u8 X86EMU_UNUSED(op1)) } break; case 2: /* call word ptr ... */ - destval = fetch_data_word(destoffset); - TRACE_AND_STEP(); - push_word(M.x86.R_IP); - M.x86.R_IP = destval; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destval = fetch_data_long(destoffset); + TRACE_AND_STEP(); + push_long(M.x86.R_EIP); + M.x86.R_EIP = destval; + } else { + destval = fetch_data_word(destoffset); + TRACE_AND_STEP(); + push_word(M.x86.R_IP); + M.x86.R_IP = destval; + } break; case 3: /* call far ptr ... */ - destval = fetch_data_word(destoffset); - destval2 = fetch_data_word(destoffset + 2); - TRACE_AND_STEP(); - push_word(M.x86.R_CS); - M.x86.R_CS = destval2; - push_word(M.x86.R_IP); - M.x86.R_IP = destval; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destval = fetch_data_long(destoffset); + destval2 = fetch_data_word(destoffset + 4); + TRACE_AND_STEP(); + push_long(M.x86.R_CS); + M.x86.R_CS = destval2; + push_long(M.x86.R_EIP); + M.x86.R_EIP = destval; + } else { + destval = fetch_data_word(destoffset); + destval2 = fetch_data_word(destoffset + 2); + TRACE_AND_STEP(); + push_word(M.x86.R_CS); + M.x86.R_CS = destval2; + push_word(M.x86.R_IP); + M.x86.R_IP = destval; + } break; case 4: /* jmp word ptr ... */ destval = fetch_data_word(destoffset); @@ -11993,11 +12077,19 @@ x86emuOp_opcFF_word_RM(u8 X86EMU_UNUSED(op1)) } break; case 2: /* call word ptr ... */ - destreg = DECODE_RM_WORD_REGISTER(rl); - DECODE_PRINTF("\n"); - TRACE_AND_STEP(); - push_word(M.x86.R_IP); - M.x86.R_IP = *destreg; + if (M.x86.mode & SYSMODE_PREFIX_DATA) { + destreg = DECODE_RM_LONG_REGISTER(rl); + DECODE_PRINTF("\n"); + TRACE_AND_STEP(); + push_long(M.x86.R_EIP); + M.x86.R_EIP = *destreg; + } else { + destreg = DECODE_RM_WORD_REGISTER(rl); + DECODE_PRINTF("\n"); + TRACE_AND_STEP(); + push_word(M.x86.R_IP); + M.x86.R_IP = *destreg; + } break; case 3: /* jmp far ptr ... */ DECODE_PRINTF("OPERATION UNDEFINED 0XFF \n"); 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