Rewrite video emulation. Features:

- slightly more accurate VGA hardware emulation;
- more int 10 functions, especially wrt to palette handling;
- first shot at graphics support;
- mode switching.

Bugs:

- graphics too slow;
- only 16 color modes work for now;
- works only under X, and only with 16 bit TrueColor visuals;
- far from being genuinely useful (I can play an old EGA game now, though
  (mahjongg.exe)).

Also, the code has been cleaned up a bit (more to come in a separate commit).

1 files changed, 275 insertions, 4 deletions

diff --git a/usr.bin/doscmd/cpu.c b/usr.bin/doscmd/cpu.c
index c273084..e0d58a7 100644
--- a/usr.bin/doscmd/cpu.c
+++ b/usr.bin/doscmd/cpu.c
@@ -1,9 +1,42 @@
 /*
-** No copyright ?!
-**
-** $FreeBSD$
-*/
+ * Copyright (c) 2001 The FreeBSD Project, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY The FreeBSD Project, Inc. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL The FreeBSD Project, Inc. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
 #include "doscmd.h"
+#include "video.h"
+
+static u_int32_t decode_modrm(u_int8_t *, u_int16_t, regcontext_t *, int *);
+static u_int8_t reg8(u_int8_t c, regcontext_t *);
+static u_int16_t reg16(u_int8_t c, regcontext_t *);
+#if 0
+static u_int32_t reg32(u_int8_t c, regcontext_t *);
+#endif
+static void write_byte(u_int32_t, u_int8_t);
+static void write_word(u_int32_t, u_int16_t);
 
 /*
 ** Hardware /0 interrupt
@@ -68,3 +101,241 @@ cpu_init(void)
     ivec[0x3e] = vec;	/* floating point emulator */
     ivec[0x3f] = vec;	/* floating point emulator */
 }
+
+/*
+ * Emulate CPU instructions. We need this for VGA graphics, at least in the 16
+ * color modes.
+ *
+ * The emulator is far from complete. We are adding the instructions as we
+ * encounter them, so this function is likely to change over time. There are
+ * no optimizations and we only emulate a single instruction at a time.
+ *
+ * As long as there is no support for DPMI or the Operand Size Override prefix
+ * we won't need the 32-bit registers. This also means that the default
+ * operand size is 16 bit.
+ */
+int
+emu_instr(regcontext_t *REGS)
+{
+    int prefix = 1;
+    u_int8_t *cs = (u_int8_t *)(R_CS << 4);
+    int ip = R_IP;
+    int instrlen;
+    int dir;
+    u_int16_t value;
+    u_int16_t seg = R_DS;
+    u_int32_t addr, endaddr;
+    
+    while (prefix) {
+	prefix = 0;
+	switch (cs[ip]) {
+	case 0x26:		/* Segment Override ES */
+	    seg = R_ES;
+	    prefix = 1;
+	    ip++;
+	    break;
+	case 0x2e:		/* Segment Override CS */
+	    seg = R_CS;
+	    prefix = 1;
+	    ip++;
+	    break;
+	case 0x36:		/* Segment Override SS */
+	    seg = R_SS;
+	    prefix = 1;
+	    ip++;
+	    break;
+	case 0x3e:		/* Segment Override DS */
+	    seg = R_DS;
+	    prefix = 1;
+	    ip++;
+	    break;
+	case 0x64:		/* Segment Override FS */
+	    seg = R_FS;
+	    prefix = 1;
+	    ip++;
+	    break;
+	case 0x65:		/* Segment Override GS */
+	    seg = R_GS;
+	    prefix = 1;
+	    ip++;
+	    break;
+	case 0x88:		/* mov r/m8, r8 */
+	    addr = decode_modrm(cs + ip, seg, REGS, &instrlen);
+	    write_byte(addr, reg8(cs[ip + 1], REGS));
+	    ip += 2 + instrlen;
+	    break;
+	case 0xc6:		/* mov r/m8, imm8 */
+	    addr = decode_modrm(cs + ip, seg, REGS, &instrlen);
+	    write_byte(addr, cs[ip + 2 + instrlen]);
+	    ip += 2 + instrlen + 1;
+	    break;
+	case 0xc7:		/* mov r/m32/16, imm32/16 */
+	    addr = decode_modrm(cs + ip, seg, REGS, &instrlen);
+	    value = *(u_int16_t *)&cs[ip + 2 + instrlen];
+	    write_word(addr, value);
+	    ip += 2 + instrlen + 2;
+	    break;
+	case 0xab:		/* stos m32/16*/
+	    break;
+	case 0xf3:		/* rep */
+	    switch (cs[++ip]) {
+	    case 0xab:		/* stos m32/16 */
+		value = R_AX;
+		/* direction */
+		dir = (R_EFLAGS & PSL_D) ? -1 : 1;
+		addr = MAKEPTR(R_ES, R_DI);
+		endaddr = MAKEPTR(R_ES, R_DI) + dir * R_CX;
+		if (addr <= endaddr)
+		    while (addr <= endaddr) {
+			write_word(addr, value);
+			addr += 2;
+		    }
+		else
+		    while (addr >= endaddr) {
+			write_word(addr, value);
+			addr -= 2;
+		    }
+		ip += 2;
+		break;
+	    default:
+		R_IP = ip--;	/* Move IP back to the 'rep' instruction */
+		return -1;
+	    }
+	    break;
+	default:
+	    /* unknown instruction, get out of here and let trap.c:sigbus()
+	       catch it. */
+	    return -1;
+	}
+	R_IP = ip;
+    }
+
+    return 0;
+}
+
+/* Decode the ModR/M byte. Returns the memory address of the operand. 'c'
+   points to the current instruction, 'seg' contains the value for the current
+   base segment; this is usually 'DS', but may have been changed by a segment
+   override prefix. We return the length of the current instruction in
+   'instrlen' so we can adjust 'IP' on return.
+
+   XXX We will probably need a second function for 32-bit instructions.
+
+   XXX We do not check for undefined combinations, like Mod=01, R/M=001. */
+static u_int32_t
+decode_modrm(u_int8_t *c, u_int16_t seg, regcontext_t *REGS, int *instrlen)
+{
+    u_int32_t	addr = 0;		/* absolute address */
+    int16_t	dspl = 0;		/* displacement, signed */
+    *instrlen = 0;
+    
+    switch (c[1] & 0xc0) {	/* decode Mod */
+    case 0x00:			/* DS:[reg] */
+	/* 'reg' is selected in the R/M bits */
+	break;
+    case 0x40:			/* 8 bit displacement */
+	dspl = (int16_t)(int8_t)c[2];
+	*instrlen = 1;
+	break;
+    case 0x80:			/* 16 bit displacement */
+	dspl = *(int16_t *)&c[2];
+	*instrlen = 2;
+	break;
+    case 0xc0:			/* reg in R/M */
+	if (c[0] & 1)		/* 16-bit reg */
+	    return reg16(c[1], REGS);
+	else			/* 8-bit reg */
+	    return reg8(c[1], REGS);
+	break;
+    }
+    
+    switch (c[1] & 0x07) {	/* decode R/M */
+    case 0x00:
+	addr = MAKEPTR(seg, R_BX + R_SI);
+	break;
+    case 0x01:
+	addr = MAKEPTR(seg, R_BX + R_DI);
+	break;
+    case 0x02:
+	addr = MAKEPTR(seg, R_BP + R_SI);
+	break;
+    case 0x03:
+	addr = MAKEPTR(seg, R_BP + R_DI);
+	break;
+    case 0x04:
+	addr = MAKEPTR(seg, R_SI);
+	break;
+    case 0x05:
+	addr = MAKEPTR(seg, R_DI);
+	break;
+    case 0x06:
+	if ((c[1] & 0xc0) >= 0x40)
+	    addr += R_BP;
+	else {
+	    addr = MAKEPTR(seg, *(int16_t *)&c[2]);
+	    *instrlen = 2;
+	}
+	break;
+    case 0x07:
+	addr = MAKEPTR(seg, R_BX + dspl);
+	break;
+    }
+    
+    return addr;
+}
+
+static u_int8_t
+reg8(u_int8_t c, regcontext_t *REGS)
+{
+    u_int8_t	r8[] = {R_AL, R_CL, R_DL, R_BL, R_AH, R_CH, R_DH, R_BH};
+
+    /* select 'rrr' bits in ModR/M */
+    return r8[(c & 0x34) >> 3];
+}
+
+static u_int16_t
+reg16(u_int8_t c, regcontext_t *REGS)
+{
+    u_int16_t	r16[] = {R_AX, R_CX, R_DX, R_BX, R_SP, R_BP, R_SI, R_DI};
+
+    return r16[(c & 0x34) >> 3];
+}
+
+#if 0
+/* not yet */
+static u_int32_t
+reg32(u_int8_t c, regcontext_t *REGS)
+{
+    u_int32_t	r32[] = {R_EAX, R_ECX, R_EDX, R_EBX,
+			 R_ESP, R_EBP, R_ESI, R_EDI};
+
+    return r32[(c & 0x34) >> 3];
+}
+#endif
+
+/* Write an 8-bit value to the location specified by 'addr'. If 'addr' lies
+   within the video memory region, we call video.c:vga_write(). */
+static void
+write_byte(u_int32_t addr, u_int8_t val)
+{
+    if (addr >= 0xa0000 && addr < 0xb0000) {
+	vga_write(addr, val);
+    } else
+	*(u_int8_t *)addr = val;
+
+    return;
+}
+
+/* Write a 16-bit value to the location specified by 'addr'. If 'addr' lies
+   within the video memory region, we call video.c:vga_write(). */
+static void
+write_word(u_int32_t addr, u_int16_t val)
+{
+    if (addr >= 0xa0000 && addr < 0xb0000) {
+	vga_write(addr, (u_int8_t)(val & 0xff));
+	vga_write(addr + 1, (u_int8_t)((val & 0xff00) >> 8));
+    } else
+	*(u_int16_t *)addr = val;
+
+    return;
+}