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/*
* mini stub for dj64.
* Copyright (C) 2024, @stsp
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*
*/
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#define DJSTUB_API_VER 5
typedef struct
{
unsigned long edi;
unsigned long esi;
unsigned long ebp;
unsigned long resrvd;
unsigned long ebx;
unsigned long edx;
unsigned long ecx;
unsigned long eax;
unsigned short flags;
unsigned short es;
unsigned short ds;
unsigned short fs;
unsigned short gs;
unsigned short ip;
unsigned short cs;
unsigned short sp;
unsigned short ss;
} __dpmi_int_regs;
int __dpmi_int(int intno, __dpmi_int_regs* regs);
int DPMIQueryExtension(unsigned short *sel, unsigned short *off,
const char *name)
{
asm(
"push es\n"
"mov eax, 0x168a\n"
"mov esi, [ebp+16]\n" // name
"int 0x2f\n"
"test al, al\n"
"jnz fail\n"
"mov ebx, [ebp+8]\n" // sel
"mov [ebx], es\n"
"mov ebx, [ebp+12]\n"
"mov [ebx], edi\n"
"pop es\n"
"xor ah, ah\n"
"fail:\n"
);
}
static void enter_stub(unsigned sel, unsigned off,
int argc, char *argv[], int envc, char *envp[], unsigned psp,
int fd, int ver)
{
asm(
"mov eax, [ebp+32]\n" // psp
"mov ecx, [ebp+40]\n" // ver
"shl ecx, 16\n"
"or eax, ecx\n"
"mov ecx, [ebp+16]\n" // argc
"mov edx, [ebp+20]\n" // argv
"mov ebx, [ebp+24]\n" // envc
"mov esi, [ebp+28]\n" // envp
"mov edi, [ebp+36]\n" // fd
"push dword [ebp+8]\n " // sel
"push dword [ebp+12]\n" // off
"call far [ss:esp]\n"
"add esp, 8\n"
);
}
extern void* __dpmi_psp;
extern void* __dpmi_env;
static unsigned psp;
int main(int argc, char *argv[])
{
static const char *ext_nm = "DJ64STUB";
unsigned char *env = __dpmi_env;
char **envp;
unsigned short sel, off;
int envc, i, letter;
int err;
int fd;
__dpmi_int_regs regs;
if (argc == 0) {
puts("no env");
return 1;
}
for (envc = i = letter = 0;; i++) {
if (env[i] == '\0') {
letter = 0;
if (env[i + 1] == '\0')
break;
} else {
if (!letter) {
letter = 1;
envc++;
}
}
}
envp = malloc((envc + 1) * sizeof(char *));
envp[envc] = NULL;
if (envc) {
int envc2;
for (envc2 = i = letter = 0;; i++) {
if (env[i] == '\0') {
letter = 0;
if (env[i + 1] == '\0')
break;
} else {
if (!letter) {
letter = 1;
envp[envc2++] = &env[i];
}
}
}
}
asm(
"mov eax, 0\n" // alloc desc for PSP
"mov ecx, 1\n" // 1 desc
"int 31h\n"
"mov [_psp], ax\n"
"mov eax, 7\n" // set base
"mov bx, [_psp]\n"
"extern ___dpmi_psp\n"
"mov cx, [___dpmi_psp + 2]\n"
"mov dx, [___dpmi_psp]\n"
"int 31h\n"
"mov eax, 8\n" // set limit
"mov bx, [_psp]\n"
"mov cx, 0\n"
"mov dx, 0ffh\n" // to PSP size
"int 31h\n"
);
err = DPMIQueryExtension(&sel, &off, ext_nm);
if (err) {
printf("%s unsupported (%x)\n", ext_nm, err);
return 1;
}
fd = open(argv[0], O_RDONLY);
if (fd == -1) {
printf("unable to open %s: %s\n", argv[0], strerror(errno));
return 1;
}
memset(®s, 0, sizeof(regs));
/* nuke out initial stub as it is no longer needed */
regs.eax = 0x4a00;
regs.ebx = 0x10; // leave only PSP
regs.es = (unsigned)__dpmi_psp >> 4;
__dpmi_int(0x21, ®s);
enter_stub(sel, off, argc, argv, envc, envp, psp, fd, DJSTUB_API_VER);
close(fd);
puts("stub returned");
return 0;
}
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