set byte [SDA + 39h] during process termination, turn abort to fail

This is compatible to lMS-DOS which sets the flag before running
int 2Fh function 1122h [1] and clears it after closing handles and
freeing memory [2], before branching to the Parent Return Address.

The flag turns any int 24h abort response into a fail instead, to
avoid iterating infinitely during file handle closing.

[1]: https://hg.pushbx.org/ecm/msdos4/file/c057c6a1c9ad/src/DOS/ctrlc.nas#l752
[2]: https://hg.pushbx.org/ecm/msdos4/file/c057c6a1c9ad/src/DOS/ctrlc.nas#l829

Author: ecm-pushbx

kernel/entry.asm

@@ -42,6 +42,7 @@ segment HMA_TEXT
                 extern   _ErrorMode
                 extern   _InDOS
                 extern   _term_type
+                extern   _abort_progress
 %IFDEF WIN31SUPPORT
                 extern   _winInstanced
 %ENDIF ; WIN31SUPPORT
@@ -742,6 +743,9 @@ CritErrExit:
                 ; Abort processing.
                 ;
 CritErrAbort:
+		test	byte [_abort_progress], -1
+		mov	al, FAIL
+		jnz	CritErrExit
 %if 0
                 mov     ax,[_cu_psp]
                 mov     es,ax

kernel/globals.h

@@ -308,6 +308,7 @@ extern BYTE
   ASM swap_always[],                /*  "    "                              */
   ASM swap_indos[],                 /*  "    "                              */
   ASM term_type,                    /* 0 normal, 1 ^C, 2 int 24h, 3 TSR     */
+  ASM abort_progress,               /* set during process termination       */
   ASM break_flg,                    /* true if break was detected           */
   ASM break_ena;                    /* break enabled flag                   */
 extern void FAR * ASM dta;          /* Disk transfer area (kludge)          */

kernel/kernel.asm

@@ -796,6 +796,7 @@ _DayOfWeek      db      2               ; 36 - day of week
 _console_swap   db      0               ; 37 console swapped during read from dev
                 global  _dosidle_flag        
 _dosidle_flag   db      1               ; 38 - safe to call int28 if nonzero
+                global  _abort_progress
 _abort_progress db      0               ; 39 - abort in progress
                 global  _CharReqHdr
 _CharReqHdr:

kernel/task.c

@@ -588,6 +588,8 @@ VOID return_user(void)
   setvec(0x23, p->ps_isv23);
   setvec(0x24, p->ps_isv24);
 
+  abort_progress = -1;
+
   /* And free all process memory if not a TSR return      */
   network_redirector(REM_PROCESS_END);
   /* might be a good idea to do that after closing
@@ -607,6 +609,8 @@ VOID return_user(void)
   cu_psp = p->ps_parent;
   q = MK_FP(cu_psp, 0);
 
+  abort_progress = 0;
+
   irp = (iregs FAR *) q->ps_stack;
 
   irp->CS = FP_SEG(p->ps_isv22);