DOS SHELL: Apparently INT 2Eh (command shell) was not implemented. Bo…

…rrow INT 2Eh handler from DOSBox SVN to add it. This fixes certain demoscene productions that rely on INT 2Eh to direct COMMAND.COM for some demo parts

src/shell/shell.cpp

@@ -32,6 +32,8 @@
 
 extern bool dos_shell_running_program;
 
+Bitu shell_psp = 0;
+
 void CALLBACK_DeAllocate(Bitu in);
 
 Bitu call_shellstop = 0;
@@ -563,6 +565,41 @@ void AUTOEXEC_Init() {
 	AddVMEventFunction(VM_EVENT_DOS_SURPRISE_REBOOT,AddVMEventFunctionFuncPair(AUTOEXEC_ShutDown));
 }
 
+static Bitu INT2E_Handler(void) {
+	/* Save return address and current process */
+	RealPt save_ret=real_readd(SegValue(ss),reg_sp);
+	Bit16u save_psp=dos.psp();
+
+	/* Set first shell as process and copy command */
+	dos.psp(shell_psp);//DOS_FIRST_SHELL);
+	DOS_PSP psp(shell_psp);//DOS_FIRST_SHELL);
+	psp.SetCommandTail(RealMakeSeg(ds,reg_si));
+	SegSet16(ss,RealSeg(psp.GetStack()));
+	reg_sp=2046;
+
+	/* Read and fix up command string */
+	CommandTail tail;
+	MEM_BlockRead(PhysMake(dos.psp(),128),&tail,128);
+	if (tail.count<127) tail.buffer[tail.count]=0;
+	else tail.buffer[126]=0;
+	char* crlf=strpbrk(tail.buffer,"\r\n");
+	if (crlf) *crlf=0;
+
+	/* Execute command */
+	if (strlen(tail.buffer)) {
+		DOS_Shell temp;
+		temp.ParseLine(tail.buffer);
+		temp.RunInternal();
+	}
+
+	/* Restore process and "return" to caller */
+	dos.psp(save_psp);
+	SegSet16(cs,RealSeg(save_ret));
+	reg_ip=RealOff(save_ret);
+	reg_ax=0;
+	return CBRET_NONE;
+}
+
 static char const * const path_string="PATH=Z:\\";
 static char const * const comspec_string="COMSPEC=Z:\\COMMAND.COM";
 static char const * const prompt_string="PROMPT=$P$G";
@@ -915,6 +952,7 @@ void SHELL_Init() {
 
     // now COMMAND.COM has a main body and PSP segment, reflect it
     dos.psp(psp_seg);
+    shell_psp = psp_seg;
 
     {
         DOS_MCB mcb((Bit16u)(env_seg-1));
@@ -943,7 +981,13 @@ void SHELL_Init() {
 
 	/* Set up int 23 to "int 20" in the psp. Fixes what.exe */
 	real_writed(0,0x23*4,((Bit32u)psp_seg<<16));
-
+
+	/* Set up int 2e handler */
+	Bitu call_int2e=CALLBACK_Allocate();
+	RealPt addr_int2e=RealMake(psp_seg+16+1,8);
+	CALLBACK_Setup(call_int2e,&INT2E_Handler,CB_IRET_STI,Real2Phys(addr_int2e),"Shell Int 2e");
+	RealSetVec(0x2e,addr_int2e);
+
 	/* Setup environment */
 	PhysPt env_write=PhysMake(env_seg,0);
 	MEM_BlockWrite(env_write,path_string,(Bitu)(strlen(path_string)+1));