Minimal support for child processes.

Implements DOS functions 50h, 51h, 55h and expands 4Ch, adds a handler
for int-22 that terminates the emulator.

With this the in memory debugger in Turbo Pascal 5.5 works.

5 files changed, 104 insertions, 15 deletions

diff --git a/src/dos.c b/src/dos.c
index 4ac59ec..203eff0 100644
--- a/src/dos.c
+++ b/src/dos.c
@@ -892,7 +892,7 @@ static void int21_debug(void)
           ax, fn, cpuGetBX(), cpuGetCX(), cpuGetDX(), cpuGetDI(), cpuGetDS(), cpuGetES());
 }
 
-// DOS int
+// DOS int 21
 void int21()
 {
     // Check CP/M call, INT 21h from address 0x000C0
@@ -918,8 +918,19 @@ void int21()
     debug(debug_int, "D-21%04X: BX=%04X\n", cpuGetAX(), cpuGetBX());
     if(debug_active(debug_dos))
         int21_debug();
-    unsigned ax = cpuGetAX();
-    switch(ax >> 8)
+
+    // Process interrupt
+    unsigned ax = cpuGetAX(), ah = ax >> 8;
+
+    // Store SS:SP into PSP, used at return from child process
+    // According to DOSBOX, only set for certain functions:
+    if(ah != 0x50 && ah != 0x51 && ah != 0x62 && ah != 0x64 && ah < 0x6c)
+    {
+        put16(cpuGetAddress(get_current_PSP(), 0x2E), cpuGetSP());
+        put16(cpuGetAddress(get_current_PSP(), 0x30), cpuGetSS());
+    }
+
+    switch(ah)
     {
     case 0: // TERMINATE PROGRAM
         exit(0);
@@ -1070,22 +1081,17 @@ void int21()
         put16(4 * (ax & 0xFF), cpuGetDX());
         put16(4 * (ax & 0xFF) + 2, cpuGetDS());
         break;
-    case 0x26: // Create PSP (allocate segment (singleton), and copy PSP)
+    case 0x26: // Create PSP (duplicate current PSP)
     {
-        uint8_t *new_base = getptr(cpuGetAddress(cpuGetDX(), 0), 0x100);
-        uint8_t *orig = getptr(cpuGetAddress(get_current_PSP(), 0), 0x100);
-        if(!new_base || !orig)
+        uint8_t *new_psp = getptr(cpuGetAddress(cpuGetDX(), 0), 0x100);
+        uint8_t *orig_psp = getptr(cpuGetAddress(get_current_PSP(), 0), 0x100);
+        if(!new_psp || !orig_psp)
         {
             debug(debug_dos, "\tinvalid new PSP segment %04x.\n", cpuGetDX());
             break;
         }
         // Copy PSP to the new segment, 0x80 is what DOS does - this excludes command line
-        memcpy(new_base, orig, 0x80);
-        debug(debug_dos, "\tnew PSP segment %04x.\n", cpuGetDX());
-        debug(debug_dos, "\tnew PSP size %02x%02x.\n", new_base[7], new_base[6]);
-        debug(debug_dos, "\toriginal PSP segment %04x.\n", get_current_PSP());
-        debug(debug_dos, "\toriginal PSP size %02x%02x.\n", orig[7], orig[6]);
-        // TODO: Initialize PSP values: int 22h, 23h, 24h and parent PSP segment to 0
+        memcpy(new_psp, orig_psp, 0x80);
         break;
     }
     case 0x27: // BLOCK READ FROM FCB
@@ -1672,7 +1678,37 @@ void int21()
         break;
     }
     case 0x4C: // EXIT
-        exit(ax & 0xFF);
+        // Detect if our PSP is last one
+        debug(debug_dos, "\texit PSP:'%04x', PARENT:%04x.\n", get_current_PSP(),
+              get16(cpuGetAddress(get_current_PSP(), 22)));
+        if(0xFFFE == get16(cpuGetAddress(get_current_PSP(), 22)))
+            exit(ax & 0xFF);
+        else
+        {
+            // Exit to parent
+            // TODO: we must close all child file descriptors and dealocate
+            //       child memory.
+            return_code = cpuGetAX() & 0xFF;
+            // Patch INT 22h, 23h and 24h addresses to the ones saved in new PSP
+            put16(0x88, get16(cpuGetAddress(get_current_PSP(), 10)));
+            put16(0x8A, get16(cpuGetAddress(get_current_PSP(), 12)));
+            put16(0x8C, get16(cpuGetAddress(get_current_PSP(), 14)));
+            put16(0x8E, get16(cpuGetAddress(get_current_PSP(), 16)));
+            put16(0x90, get16(cpuGetAddress(get_current_PSP(), 18)));
+            put16(0x92, get16(cpuGetAddress(get_current_PSP(), 20)));
+            // Set PSP to parent
+            set_current_PSP(get16(cpuGetAddress(get_current_PSP(), 22)));
+            // Get last stack
+            cpuSetSS(get16(cpuGetAddress(get_current_PSP(), 0x30)));
+            cpuSetSP(get16(cpuGetAddress(get_current_PSP(), 0x2E)));
+            int stack = cpuGetAddress(cpuGetSS(), cpuGetSP());
+            // Fixup interrupt return
+            put16(stack, get16(0x22 * 4));
+            put16(stack + 2, get16(0x22 * 4 + 2));
+            put16(stack + 4, 0xf202);
+            // And exit!
+        }
+        break;
     case 0x4D: // GET RETURN CODE (ERRORLEVEL)
         cpuSetAX(return_code);
         return_code = 0;
@@ -1684,11 +1720,33 @@ void int21()
     case 0x4F: // FIND NEXT MATCHING FILE
         dos_find_next(0);
         break;
+    case 0x50: // SET CURRENT PSP
+        set_current_PSP(cpuGetBX());
+        break;
+    case 0x51: // GET CURRENT PSP
+        cpuSetBX(get_current_PSP());
+        break;
     case 0x52: // GET SYSVARS
         cpuSetES(dos_sysvars >> 4);
         cpuSetBX((dos_sysvars & 0xF) + 24);
-        cpuClrFlag(cpuFlag_CF);
         break;
+    case 0x55: // Create CHILD PSP
+    {
+        uint8_t *new_psp = getptr(cpuGetAddress(cpuGetDX(), 0), 0x100);
+        uint8_t *orig_psp = getptr(cpuGetAddress(get_current_PSP(), 0), 0x100);
+        if(!new_psp || !orig_psp)
+        {
+            debug(debug_dos, "\tinvalid new PSP segment %04x.\n", cpuGetDX());
+            break;
+        }
+        // Copy PSP to the new segment, 0x80 is what DOS does - this excludes command line
+        memcpy(new_psp, orig_psp, 0x80);
+        // Set parent PSP to the current one
+        new_psp[22] = get_current_PSP() & 0xFF;
+        new_psp[23] = get_current_PSP() >> 8;
+        set_current_PSP(cpuGetDX());
+        break;
+    }
     case 0x56: // RENAME
     {
         char *fname1 = dos_unix_path(cpuGetAddrDS(cpuGetDX()), 0);
@@ -1806,6 +1864,14 @@ void int21()
     }
 }
 
+// DOS int 22 - TERMINATE ADDRESS
+void int22()
+{
+    debug(debug_dos, "D-22: TERMINATE HANDLER CALLED\n");
+    // If we reached here, we must terminate now
+    exit(return_code & 0xFF);
+}
+
 static char *addstr(char *dst, const char *src, int limit)
 {
     while(limit > 0 && *src)
diff --git a/src/dos.h b/src/dos.h
index 0ead371..412f580 100644
--- a/src/dos.h
+++ b/src/dos.h
@@ -6,4 +6,5 @@
 void init_dos(int argc, char **argv);
 void int20(void);
 void int21(void);
+void int22(void);
 void int28(void);
diff --git a/src/loader.c b/src/loader.c
index 1d8225f..7c6c839 100644
--- a/src/loader.c
+++ b/src/loader.c
@@ -666,6 +666,20 @@ uint16_t create_PSP(const char *cmdline, const char *environment, int env_size,
     dosPSP[7] = 0xFE;                   //     this jumps to 0xC0, where an
     dosPSP[8] = 0x1D;                   //     INT 21h is patched.
     dosPSP[9] = 0xF0;
+    dosPSP[10] = 0x22;                  // Handler for INT 22h
+    dosPSP[11] = 0x00;
+    dosPSP[12] = 0x00;
+    dosPSP[13] = 0x00;
+    dosPSP[14] = 0x23;                  // Handler for INT 23h
+    dosPSP[15] = 0x00;
+    dosPSP[16] = 0x00;
+    dosPSP[17] = 0x00;
+    dosPSP[18] = 0x24;                  // Handler for INT 24h
+    dosPSP[19] = 0x00;
+    dosPSP[20] = 0x00;
+    dosPSP[21] = 0x00;
+    dosPSP[22] = 0xFE;                  // 16: Parent PSP, use special value of FFFE
+    dosPSP[23] = 0xFF;                  //     to signal no parent DOS process
     dosPSP[44] = 0xFF & env_seg;        // 2C: environment segment
     dosPSP[45] = 0xFF & (env_seg >> 8); //
     dosPSP[80] = 0xCD;                  // 50: INT 21h / RETF
@@ -698,6 +712,11 @@ unsigned get_current_PSP(void)
     return current_PSP;
 }
 
+void set_current_PSP(unsigned psp_seg)
+{
+    current_PSP = psp_seg;
+}
+
 static int g16(uint8_t *buf)
 {
     return buf[0] + (buf[1] << 8);
diff --git a/src/loader.h b/src/loader.h
index 6f5bfa1..b44f414 100644
--- a/src/loader.h
+++ b/src/loader.h
@@ -7,6 +7,7 @@
 uint16_t create_PSP(const char *cmdline, const char *environment, int env_size,
                     const char *progname);
 unsigned get_current_PSP(void);
+void set_current_PSP(unsigned psp_seg);
 
 // DOS Memory handling
 int mem_resize_segment(int seg, int size);
diff --git a/src/main.c b/src/main.c
index 9bc5b09..d0c0d2f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -84,6 +84,8 @@ void bios_routine(unsigned inum)
         int21();
     else if(inum == 0x20)
         int20();
+    else if(inum == 0x22)
+        int22();
     else if(inum == 0x1A)
         int1A();
     else if(inum == 0x19)