Apply fix contributed by George Koehler:

- don't crash if BSS overlaps BDOS
- fix stack initialisation bug
- fix command line argification

diff --git a/plat/cpm/boot.s b/plat/cpm/boot.s
index b36d1ce..960dc40 100644 (file)
--- a/plat/cpm/boot.s
+++ b/plat/cpm/boot.s
@@ -15,12 +15,21 @@ MAX_ARGV = 8
 .sect .bss
 STACKSIZE = 2*1024
 .comm stack, STACKSIZE
-.comm oldstack, 2
 
 .sect .text
 begtext:
-       ! The absolute first thing we have to do is to clear the bss. (argify
-       ! requires it.)
+       ! Check if bss would overlap BDOS.  We must not overwrite
+       ! BDOS and crash CP/M.  We cheat by comparing only high bytes
+       ! of each address.
+
+       lxi b, __end
+       lda 0x0007
+       mov c, a                ! c = high byte of BDOS address
+       mov a, b                ! a = high byte of _end
+       cmp c
+       jnc __exit              ! emergency exit if a >= c
+
+       ! We have to clear the bss. (argify requires it.)
        
        lxi h, begbss
        lxi b, endbss
@@ -36,8 +45,8 @@ begtext:
        jnz 1b
 
        ! Set up the stack (now it's been cleared, since it's in the BSS).
-               
-       lxi sp, oldstack + STACKSIZE
+
+       lxi sp, stack + STACKSIZE
 
        ! C-ify the command line at 0x0080.
        
@@ -54,43 +63,38 @@ begtext:
        ! Now argify it.
        
        lxi b, 0x0081            ! bc = command line pointer
-       lxi d, argv              ! de = argv pointer
-               
-       ldax b                   ! peek for any leading whitespace
-       ora a
-       cpi ' '
-       jz 3f
-       
-1:  xchg                     ! write out the next argument
-    mov m, c
-    inx h
-    mov m, b
-    inx h
-    xchg
-
-       lda argc                 ! exit if this was the last argument
+       lxi h, argv              ! hl = argv pointer
+
+loop_of_argify:
+       ldax b                  ! a = next character
+       ora a                   ! check for end of string
+       jz end_of_argify
+       cpi ' '                 ! scan for non-space
+       jz 2f
+
+       mov m, c                ! put next argument in argv
+       inx h
+       mov m, b
+       inx h
+
+       lda argc                ! increment argc
        inr a
        sta argc
-       cpi MAX_ARGV
-    jz end_of_argify
-    
-2:  inx b                    ! scan for whitespace
-    ldax b
-    ora a
-    jz end_of_argify
-    cpi ' '
-    jnz 2b
-    
-    xra a                    ! replace the space with a \0
-    stax b
-    
-3:  inx b                    ! scan for non-whitespace
-    ldax b
-    ora a
-    jz end_of_argify
-    cpi ' '
-    jz 3b
-    jmp 1b
+       cpi MAX_ARGV            ! exit loop if argv is full
+       jz end_of_argify
+
+1:     inx b                   ! scan for space
+       ldax b
+       ora a
+       jz end_of_argify
+       cpi ' '
+       jnz 1b
+
+       xra a                   ! replace the space with a '\0'
+       stax b
+
+2:     inx b
+       jmp loop_of_argify
 end_of_argify:
 
        ! Add the fake parameter for the program name.
@@ -110,8 +114,8 @@ end_of_argify:
        mvi h, 0
        push h
        call __m_a_i_n
-       jmp EXIT
-       
+       ! FALLTHROUGH
+
 ! Emergency exit routine.
 
 .define EXIT, __exit