wendt@arizona.edu (Alan Lee Wendt) (05/21/88)
Problem: sbrk wraps the break, returning a low number.
Symptom: Segmentation violations. On my system attempts to
backtrace the problem in the debugger crash the system.
System: 80286 Venix V Rev 2.2, but examine other Sys V
in case it's generic.
Reproduce: Set the break to 65022 with a series of sbrk calls.
Then do sbrk(526). My system will set the new break
to 12.
Fix: I added a jump on no-carry (jnb) around some code that
sets the errno to ENOMEM and returns -1. If the addition
to get the new break wraps, it will set the carry and
fall into the error case.
You'll need to disassemble brk.o in /lib/libc. The
routine brk is also in brk.o but is not shown here
because it doesn't need changes.
Apologies for the hard constants.
Fixer: Alan Wendt
.globl _end
.comm _errno,2
.data
.even
_loc: .word _end
.text
.globl _sbrk
_sbrk: push bp
mov bp,sp
mov bx,#17
mov ax,*4(bp)
add ax,_loc
jnb _try *new
mov _errno,*12 *new
mov ax,*-1 *new
j _out1 *new
_try: *new
int 241
jcxz _ok1
mov _errno,cx
j _out1
_ok1: mov bx,_loc
mov ax,bx
add bx,*4(bp)
mov _loc,bx
_out1: pop bp
ret