kill + ps: implement SYS_KILL (pid 1 immortal) and a ps tool

- PCB gains PROC_PROG (running program id), set by exec, inherited on fork.
- sys_kill(pid): reject pid 1 (immortal) and unknown/dead pids; mark the target
  zombie, reparent its children to init, wake its parent if blocked in wait;
  schedule away if a process kills itself. Reuses FindPcbByPid/ReparentToInit.
- sys_ps(slot,buf)->{pid,state,prog}; sys_progname(id) via NameTable reverse
  lookup. NameTable gains sh/ps/kill.
- libc: kill/psget/progname; tools ps (pid state cmd) and kill <pid>.
- verified: ps lists sh(B)+ps(R); kill 1 refused; kill 42 fails.

10 files changed, 260 insertions, 5 deletions

diff --git a/Makefile b/Makefile
index 9b871fa..e2a86eb 100644
--- a/Makefile
+++ b/Makefile
@@ -20,7 +20,7 @@ $(BUILD)/%.o: src/%.asm | $(BUILD)
 # C programs: compiled with SDCC into ROM-bank blobs and INCBIN'd by programs.asm
 CBLOBS := c/chello.bin c/echo.bin c/true.bin c/false.bin c/uname.bin \
           c/pid.bin c/cat.bin c/wc.bin c/head.bin c/args.bin \
-          c/ls.bin c/save.bin c/rm.bin c/sh.bin
+          c/ls.bin c/save.bin c/rm.bin c/sh.bin c/ps.bin c/kill.bin
 $(BUILD)/programs.o: $(CBLOBS)
 
 # C programs also depend on the shared libc sources
diff --git a/c/gbos.h b/c/gbos.h
index fa926fd..5f22a5a 100644
--- a/c/gbos.h
+++ b/c/gbos.h
@@ -38,4 +38,7 @@ unsigned char wait(void);
 void          setin(unsigned char fd);      /* redirect stdin  ($FF=console) */
 void          setout(unsigned char fd);     /* redirect stdout ($FF=console) */
 unsigned char lookup(const char *name);     /* command name -> program id    */
+unsigned char kill(unsigned char pid);      /* terminate a pid (1 is immortal)*/
+unsigned char psget(unsigned char slot, unsigned char *buf); /* {pid,state,prog}*/
+void          progname(unsigned char id, char *buf);         /* id -> name     */
 #endif
diff --git a/c/kill.c b/c/kill.c
new file mode 100644
index 0000000..e524627
--- /dev/null
+++ b/c/kill.c
@@ -0,0 +1,10 @@
+#include "gbos.h"
+/* kill <pid>: terminate a process (pid 1 is immortal). */
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    unsigned char pid;
+    if (argc < 1) { puts("usage: kill <pid>"); nl(); return; }
+    pid = atou(argv[0]);
+    if (kill(pid)) { puts("kill: no such pid (or immortal)"); nl(); }
+}
diff --git a/c/libc.s b/c/libc.s
index 857a16d..bcc8199 100644
--- a/c/libc.s
+++ b/c/libc.s
@@ -167,3 +167,23 @@ _lookup:
 	ld	c, #19			; SYS_LOOKUP
 	rst	#0x30
 	ret
+
+	.globl _kill, _psget, _progname
+	;; unsigned char kill(unsigned char pid /*A*/) -> A (0 ok, $FF fail)
+_kill:
+	ld	b, a
+	ld	c, #9			; SYS_KILL
+	rst	#0x30
+	ret
+	;; unsigned char psget(unsigned char slot /*A*/, unsigned char *buf /*DE*/) -> A
+_psget:
+	ld	b, a
+	ld	c, #20			; SYS_PS
+	rst	#0x30
+	ret
+	;; void progname(unsigned char id /*A*/, char *buf /*DE*/)
+_progname:
+	ld	b, a
+	ld	c, #21			; SYS_PROGNAME
+	rst	#0x30
+	ret
diff --git a/c/ps.c b/c/ps.c
new file mode 100644
index 0000000..7bfc0de
--- /dev/null
+++ b/c/ps.c
@@ -0,0 +1,14 @@
+#include "gbos.h"
+/* ps: list live processes (pid, state, command). */
+void main(void) {
+    unsigned char i, buf[3];
+    char name[9];
+    for (i = 0; i < 8; i++) {
+        if (psget(i, buf)) {              /* buf = {pid, state, prog} */
+            putu(buf[0]); putc(' ');
+            putc("-RrBZ"[buf[1]]); putc(' ');
+            progname(buf[2], name);
+            puts(name); nl();
+        }
+    }
+}
diff --git a/include/gbos.inc b/include/gbos.inc
index 6aaaf73..30c3a50 100644
--- a/include/gbos.inc
+++ b/include/gbos.inc
@@ -69,8 +69,11 @@ DEF PROC_PARENT RB 1
 DEF PROC_EXIT   RB 1    ; exit code (valid when PS_ZOMBIE)
 DEF PROC_STDIN  RB 1    ; $FF = console, else an open-file fd
 DEF PROC_STDOUT RB 1    ; $FF = console, else an open-file fd
+DEF PROC_PROG   RB 1    ; program id currently running ($FF = none), for ps
 DEF PROC_SIZE   RB 0
 
+DEF KILL_CODE   EQU 137 ; exit status of a killed process (128 + SIGKILL)
+
 DEF STD_CONSOLE EQU $FF
 
 ; -----------------------------------------------------------------------------
@@ -96,7 +99,10 @@ DEF SYS_PUTC    EQU 16   ; write a byte to stdout         (E=byte)
 DEF SYS_SETIN   EQU 17   ; set current stdin  fd          (B=fd, $FF=console)
 DEF SYS_SETOUT  EQU 18   ; set current stdout fd          (B=fd, $FF=console)
 DEF SYS_LOOKUP  EQU 19   ; program id for a command name  (DE=name -> A=id/$FF)
-DEF SYS_MAX     EQU 20
+DEF SYS_PS      EQU 20   ; process table entry            (B=slot, DE=buf3 -> A=1/0)
+DEF SYS_PROGNAME EQU 21  ; program id -> name             (B=id, DE=namebuf)
+DEF SYS_MAX     EQU 22
+; SYS_KILL (9) is now implemented (B=pid -> A=0/$FF; pid 1 is immortal)
 ; (SYS_OPEN=4 / SYS_CLOSE=5 are now implemented by the filesystem)
 
 ; -----------------------------------------------------------------------------
@@ -138,5 +144,8 @@ DEF PROG_ARGS   EQU 12
 DEF PROG_LS     EQU 13
 DEF PROG_SAVE   EQU 14
 DEF PROG_RM     EQU 15
+DEF PROG_PS     EQU 16
+DEF PROG_KILL   EQU 17
+DEF PROG_SPIN   EQU 18
 
     ENDC
diff --git a/src/kdata.asm b/src/kdata.asm
index ea18756..b299021 100644
--- a/src/kdata.asm
+++ b/src/kdata.asm
@@ -46,3 +46,6 @@ wFsSlot::    DS 1
 wFsByte::    DS 1
 wFsOFPtr::   DS 2
 wKChar::     DS 1       ; scratch for KPutc
+wKillParent::DS 1       ; scratch for sys_kill
+wPsBuf::     DS 2       ; scratch for sys_ps
+wPnStart::   DS 2       ; scratch for sys_progname
diff --git a/src/proc.asm b/src/proc.asm
index ab1c807..cd79160 100644
--- a/src/proc.asm
+++ b/src/proc.asm
@@ -224,7 +224,9 @@ ProcCreate::
     ld [hl+], a                 ; PROC_EXIT
     ld a, STD_CONSOLE
     ld [hl+], a                 ; PROC_STDIN  = console
-    ld [hl], a                  ; PROC_STDOUT = console
+    ld [hl+], a                 ; PROC_STDOUT = console
+    ld a, $FF
+    ld [hl], a                  ; PROC_PROG   = none
 
     ; build the initial stack frame in the task's RAM bank
     ld a, [wTmpEntry]
@@ -453,7 +455,10 @@ sys_fork::
     ld [hl+], a                 ; child STDIN = parent STDIN
     inc de
     ld a, [de]
-    ld [hl], a                  ; child STDOUT = parent STDOUT
+    ld [hl+], a                 ; child STDOUT = parent STDOUT
+    inc de
+    ld a, [de]
+    ld [hl], a                  ; child PROC_PROG = parent PROC_PROG
 
     ; ---- return to the parent with child pid ----
     ld a, [wForkUserSP]
@@ -484,6 +489,15 @@ sys_fork::
 ; our demo programs keep no pre-initialized RAM.
 ; =============================================================================
 sys_exec::
+    ; record the running program id in the PCB (for ps)
+    ld a, [wCurProc]
+    add PROC_PROG
+    ld l, a
+    ld a, [wCurProc+1]
+    adc 0
+    ld h, a
+    ld a, b
+    ld [hl], a
     ; HL = &ProgramTable[B] = ProgramTable + B*4
     ld hl, ProgramTable
     ld a, b
diff --git a/src/programs.asm b/src/programs.asm
index 1a7092e..f21d40b 100644
--- a/src/programs.asm
+++ b/src/programs.asm
@@ -88,6 +88,12 @@ ProgSave:
 SECTION "prog_rm",     ROMX[$4000], BANK[17]
 ProgRm:
     INCBIN "c/rm.bin"
+SECTION "prog_ps",     ROMX[$4000], BANK[18]
+ProgPs:
+    INCBIN "c/ps.bin"
+SECTION "prog_kill",   ROMX[$4000], BANK[19]
+ProgKill:
+    INCBIN "c/kill.bin"
 
 ; -----------------------------------------------------------------------------
 ; PROG_SH (bank 3) - the shell, now written in C (c/sh.c): parses >/</| and
@@ -162,6 +168,10 @@ ProgramTable::
     dw ProgSave
     db LOW(BANK(ProgRm)), HIGH(BANK(ProgRm))
     dw ProgRm
+    db LOW(BANK(ProgPs)), HIGH(BANK(ProgPs))
+    dw ProgPs
+    db LOW(BANK(ProgKill)), HIGH(BANK(ProgKill))
+    dw ProgKill
 
 ; -----------------------------------------------------------------------------
 ; NameTable (ROM0) - command name -> program id, searched by sys_lookup.
@@ -198,4 +208,10 @@ NameTable::
     db PROG_SAVE
     db "rm", 0
     db PROG_RM
+    db "sh", 0
+    db PROG_SH
+    db "ps", 0
+    db PROG_PS
+    db "kill", 0
+    db PROG_KILL
     db 0
diff --git a/src/syscall.asm b/src/syscall.asm
index f149a76..0b47c05 100644
--- a/src/syscall.asm
+++ b/src/syscall.asm
@@ -43,7 +43,7 @@ SyscallTable:
     dw sys_exec                 ; 6  EXEC
     dw sys_wait                 ; 7  WAIT
     dw sys_getpid               ; 8  GETPID
-    dw sys_nosys                ; 9  KILL  (TODO)
+    dw sys_kill                 ; 9  KILL
     dw sys_nosys                ; 10 BRK   (TODO)
     dw sys_yield                ; 11 YIELD
     dw sys_getb                 ; 12 GETB
@@ -54,6 +54,8 @@ SyscallTable:
     dw sys_setin                ; 17 SETIN
     dw sys_setout               ; 18 SETOUT
     dw sys_lookup               ; 19 LOOKUP
+    dw sys_ps                   ; 20 PS
+    dw sys_progname             ; 21 PROGNAME
 
 ; -----------------------------------------------------------------------------
 sys_nosys:
@@ -388,3 +390,167 @@ sys_wait:
 .nochild
     ld a, $FF
     ret
+
+; =============================================================================
+; sys_kill(B = pid) -> A = 0 ok / $FF fail. pid 1 (init/shell) is immortal.
+; Terminates the target: mark zombie, reparent its children to init, wake its
+; parent if blocked in wait. If we killed ourselves, schedule away forever.
+; =============================================================================
+sys_kill::
+    ld a, b
+    cp INIT_PID
+    jr z, .fail                 ; init is immortal
+    call FindPcbByPid           ; A=pid -> DE=&PCB, CF if not found (B preserved=pid)
+    jr c, .fail
+    ld a, [de]                  ; state
+    cp PS_FREE
+    jr z, .fail
+    cp PS_ZOMBIE
+    jr z, .fail                 ; already dead
+    ; mark ZOMBIE
+    ld a, PS_ZOMBIE
+    ld [de], a
+    ; PROC_EXIT = KILL_CODE
+    ld a, e
+    add PROC_EXIT
+    ld l, a
+    ld a, d
+    adc 0
+    ld h, a
+    ld a, KILL_CODE
+    ld [hl], a
+    ; victim's parent pid
+    ld a, e
+    add PROC_PARENT
+    ld l, a
+    ld a, d
+    adc 0
+    ld h, a
+    ld a, [hl]
+    ld [wKillParent], a
+    ; reparent victim's children to init (B still = victim pid)
+    ld a, b
+    ld [wExitMyPid], a
+    call ReparentToInit
+    ; wake victim's parent if it is blocked in wait()
+    ld a, [wKillParent]
+    call FindPcbByPid
+    jr c, .maybe_self
+    ld a, [de]
+    cp PS_BLOCKED
+    jr nz, .maybe_self
+    ld a, PS_READY
+    ld [de], a
+.maybe_self
+    ; if the victim is the current process, don't return to it
+    ld a, [wCurProc]
+    add PROC_PID
+    ld l, a
+    ld a, [wCurProc+1]
+    adc 0
+    ld h, a
+    ld a, [wExitMyPid]
+    cp [hl]
+    jr nz, .ok
+.dead
+    call SchedYield
+    jr .dead
+.ok
+    xor a
+    ret
+.fail
+    ld a, $FF
+    ret
+
+; =============================================================================
+; sys_ps(B = slot, DE = buf[3]) -> A = 1 if used (buf = pid,state,prog), else 0
+; =============================================================================
+sys_ps::
+    ld a, e
+    ld [wPsBuf], a
+    ld a, d
+    ld [wPsBuf+1], a
+    ld a, b
+    cp MAX_PROCS
+    jr nc, .no
+    call PcbPtr                 ; DE = &PCB[slot]
+    ld a, [de]                  ; state
+    cp PS_FREE
+    jr z, .no
+    ld a, [wPsBuf]
+    ld l, a
+    ld a, [wPsBuf+1]
+    ld h, a                     ; HL = buf
+    push de                     ; PCB
+    ld a, e
+    add PROC_PID
+    ld e, a
+    ld a, d
+    adc 0
+    ld d, a
+    ld a, [de]                  ; pid
+    ld [hl+], a
+    pop de
+    push de
+    ld a, [de]                  ; state
+    ld [hl+], a
+    pop de
+    ld a, e
+    add PROC_PROG
+    ld e, a
+    ld a, d
+    adc 0
+    ld d, a
+    ld a, [de]                  ; prog id
+    ld [hl], a
+    ld a, 1
+    ret
+.no
+    xor a
+    ret
+
+; =============================================================================
+; sys_progname(B = id, DE = namebuf) - copy the command name for a program id.
+; =============================================================================
+sys_progname::
+    ld hl, NameTable
+.l
+    ld a, [hl]
+    or a
+    jr z, .none
+    ld a, l
+    ld [wPnStart], a
+    ld a, h
+    ld [wPnStart+1], a
+.sk
+    ld a, [hl+]
+    or a
+    jr nz, .sk                  ; HL now at the id byte
+    ld a, [hl]
+    cp b
+    jr z, .match
+    inc hl                      ; skip id -> next entry
+    jr .l
+.match
+    ld a, [wPnStart]
+    ld l, a
+    ld a, [wPnStart+1]
+    ld h, a
+    ld b, 8
+.cp
+    ld a, [hl+]
+    ld [de], a
+    inc de
+    or a
+    jr z, .done
+    dec b
+    jr nz, .cp
+.done
+    ret
+.none
+    ld a, $3F                   ; '?'
+    ld [de], a
+    inc de
+    xor a
+    ld [de], a
+    ret