We can now load and run 32-bit protected-mode executables. We have not,

however, set up the data segment.

plat/msdos386/boot.s

@@ -11,144 +11,12 @@
 .sect .bss
 
 .sect .text
-.use16
-exe_header:
-    .data2 0x5a4d               ! magic number
-    .data2 0                    ! number of bytes in last loadable page
-    .data2 exe_text_paras       ! size of .exe, in pages
-    .data2 0                    ! number of relocation entries
-    .data2 0                    ! start of loadable area, in 16-byte paragraphs
-    .data2 exe_ram_paras        ! required RAM size, in 16-byte paragraphs
-    .data2 0                    ! maximum RAM siz, in 16-byte paragraphse
-    .data2 0                    ! initial SS, relative to program
-    .data2 exe_stack            ! initial SP
-    .data2 0                    ! checksum (ignored)
-    .data2 exe_start            ! initial IP
-    .data2 0                    ! initial CS, relative to program
-    .data2 0                    ! offset of relocation table
-    .data2 0                    ! overlay number
-
-dpmi_edi    = 0x00
-dpmi_esi    = 0x04
-dpmi_ebp    = 0x08
-dpmi_ebx    = 0x10
-dpmi_edx    = 0x14
-dpmi_ecx    = 0x18
-dpmi_eax    = 0x1c
-dpmi_flags  = 0x20
-dpmi_es     = 0x22
-dpmi_ds     = 0x24
-dpmi_fs     = 0x26
-dpmi_gs     = 0x28
-dpmi_ip     = 0x2a
-dpmi_cs     = 0x2c
-dpmi_sp     = 0x2e
-dpmi_ss     = 0x30
-
-dpmi_rs     = 0x32 ! WORD: real segment
-dpmi_psp    = 0x34 ! WORD: PSP segment
-dpmi_switch = 0x38 ! DWORD: far pointer of pmode switch routine
-
-    .seek 0x3c
-exe_start:
-    ! On entry, DS=ES=PSP. Make DS=CS, so we're running in tiny mode.
-
-    push cs
-    pop ds
-    mov (dpmi_rs), ds
-    mov (dpmi_psp), es
-
-    ! Initialise DPMI.
-
-    mov ax, 0x1687
-    int 0x2f
-    or ax, ax
-    jnz no_dpmi
-    mov (dpmi_switch+0), di     ! write back PMODE switch routine
-    mov (dpmi_switch+2), es
-    or si, si                   ! do we need a DPMI private area?
-    jz 1f
-
-    mov bx, si
-    movb ah, 0x48
-    int 0x21                    ! allocate memory from DOS
-    mov es, ax                  ! data area segment -> es
-1:
-    ! Switch to protected mode.
-
-    mov ax, 1                   ! 32-bit app
-    callf (dpmi_switch)
-    jnc pmode                   ! Success!
-
-    ! Could not switch to protected mode.
-
-    mov dx, no_pmode_msg
-    jmp exit_with_error
-
-no_dpmi:
-    mov dx, no_dpmi_msg
-    ! fall through
-
-! Displays the message in dx and exits.
-exit_with_error:
-    movb ah, 9
-    int 0x21                    ! print $-terminated string
-    mov ax, 0x4cff
-    int 0x21                    ! terminate with error code al
-
-pmode:
-    ! We're now in protected mode! Switch our code segment to 32-bit mode.
-
-    mov cx, cs
-    lar cx, cx
-    movb cl, ch
-    movb ch, 0xc0
-    mov bx, cs
-    mov ax, 0x0009
-    int 0x31                    ! Make selector 32 bit
-
-    .use32
-    o16 mov (dpmi_edx), go_msg
-    o16 mov ax, (dpmi_rs)
-    o16 mov (dpmi_ds), ax
-    movb (dpmi_eax+1), 9
-    call int21
-    o16 mov ax, 0x4c00
-    int 0x21
-
-    ! Simulate DOS interrupt bx.
-int21:
-    o16 mov bx, 0x21
-callint:
-    o16 xor ax, ax
-    o16 mov (dpmi_ss), ax           ! zero stack: DPMI host allocates one.
-    o16 mov (dpmi_sp), ax
-    push ds
-    pop es
-    mov di, ax
-    o16 mov ax, 0x300
-    int 0x31                    ! simulate DOS interrupt
-    push cs
-    pop ds
-    ret
-
-go_msg:
-    .ascii "Go!$"
-no_pmode_msg:
-    .ascii "Couldn't switch to protected mode$"
-no_dpmi_msg:
-    .ascii "No DPMI$"
-
-exe_top:
-
-exe_stack = exe_top + 512
-exe_text_paras = [exe_top - exe_header + 511] / 512
-exe_ram_paras = [exe_stack - exe_top + 15] / 16
-
-
 #define STACK_BUFFER 128 /* number of bytes to leave for stack */
 
 begtext:
+    mov eax, 0x4c00
+    int 0x21
+
     ! Make sure we are running under MS-DOS 2 or above.
     !
     ! While at it, also remember the actual DOS version, so that we know

plat/msdos386/build-pkg.lua

@@ -6,6 +6,32 @@ ackfile {
 	vars = { plat = "msdos386" }
 }
 
+ackfile {
+	name = "stub",
+	srcs = { "./stub.s" },
+	vars = { plat = "msdos386" }
+}
+
+normalrule {
+	name = "stub_aout",
+	ins = {
+		"util/led+led",
+		"+stub"
+	},
+	outleaves = { "stub.aout" },
+	commands = { "%{ins[1]} %{ins[2]} -o %{outs[1]}" }
+}
+
+normalrule {
+	name = "stub_exe",
+	ins = {
+		"util/amisc+aslod",
+		"+stub_aout"
+	},
+	outleaves = { "stub.exe" },
+	commands = { "%{ins[1]} %{ins[2]} %{outs[1]}" }
+}
+
 build_plat_libs {
 	name = "libs",
 	arch = "i386",
@@ -19,6 +45,7 @@ installable {
 		"+libs",
         "./include+pkg",
 		["$(PLATIND)/msdos386/boot.o"] = "+boot",
+		["$(PLATIND)/msdos386/stub.exe"] = "+stub_exe",
         ["$(PLATIND)/msdos386/libsys.a"] = "./libsys+lib",
 	}
 }

plat/msdos386/descr

@@ -72,6 +72,6 @@ name cv
 	from .out
 	to .exe
 	program {EM}/bin/aslod
-	args < >
+	args -p {PLATFORMDIR}/stub.exe < >
 	outfile msdos386.exe
 end

plat/msdos386/stub.s

@@ -162,7 +162,7 @@ exe_start:
     mov bx, (fh)
     mov ax, 0x4200
     xor cx, cx                  ! high offset
-    xor dx, dx                  ! low offset
+    mov dx, text_top            ! low offset
     int 0x21                    ! lseek
 
     o32 xor edi, edi            ! destination 32-bit register
@@ -194,7 +194,7 @@ exe_start:
     o32 mov eax, (pmemhandle)
     o32 movzx ebx, (rseg)
     push es
-    push text_top
+    push 0
     retf
 
 bad_dpmi:
@@ -225,12 +225,6 @@ exit_with_error:
     mov ax, 0x4cff
     int 0x21                    ! terminate with error code al
 
-pmode:
-    .use32
-    mov ax, 0x4c00
-    int 0x21
-    .use16
-
     ! Simulate DOS interrupt.
 int21:
     mov (dpmi_eax), ax
@@ -266,6 +260,7 @@ no_file_msg:
     .asciz "Couldn't open .exe"
 no_dpmi_msg:
     .asciz "No DPMI host installed"
+.align 2
 text_top:
 
 exe_text_pages = [text_top - exe_header + 511] / 512

util/amisc/aslod.1

@@ -3,7 +3,7 @@
 aslod \- ACK simple loader
 .SH SYNOPSIS
 .B aslod
-[\-h] [\-v] inputfile outputfile
+[\-h] [\-v] [\-p prefixfile] inputfile outputfile
 .SH DESCRIPTION
 .I aslod
 converts an absolute ack.out file into a simple binary memory dump.
@@ -16,5 +16,8 @@ The file must have all references resolved and be linked to a
 fixed address. aslod will dump the segments, in order, such
 that the first byte of TEXT is at offset 0 in the file
 (regardless of where it is in memory).
+.PP
+If a prefix file is specified, this is prepended to the output before writing.
+No changes to the output itself are made.
 .SH "SEE ALSO"
 ack.out(5)

util/amisc/aslod.c

@@ -37,6 +37,7 @@ struct outsect outsect[S_MAX];
 char* stringarea;
 
 char* outputfile = NULL;                /* Name of output file, or NULL */
+char* prefixfile = NULL;				/* Name of prefix file, or NULL */
 char* program;                          /* Name of current program: argv[0] */
 
 FILE* input;                            /* Input stream */
@@ -136,6 +137,19 @@ void emits(struct outsect* section, struct outsect* nextsect)
 	}
 }
 
+void emitprefixfile(void)
+{
+	FILE* fp = fopen(prefixfile, "rb");
+
+	while (!feof(fp))
+	{
+		char buffer[BUFSIZ];
+		size_t blocksize = fread(buffer, 1, BUFSIZ, fp);
+		writef(buffer, 1, blocksize);
+	}
+
+	fclose(fp);
+}
 
 /* Macros from modules/src/object/obj.h */
 #define Xchar(ch)	((ch) & 0377)
@@ -204,6 +218,12 @@ int main(int argc, char* argv[])
 				verbose = true;
 				break;
 
+			case 'p':
+				argv++;
+				argc--;
+				prefixfile = argv[1];
+				break;
+
 			default:
 			syntaxerror:
 				fatal("syntax error --- try -h for help");
@@ -288,6 +308,8 @@ int main(int argc, char* argv[])
 
 	/* And go! */
 	
+	if (prefixfile)
+		emitprefixfile();
 	emits(&outsect[TEXT], &outsect[ROM]);
 	emits(&outsect[ROM], &outsect[DATA]);
 	emits(&outsect[DATA], NULL);