I've noticed this some time ago and, while it doesn't seem to be
a problem in practice, it's still undefined. C says what happens with
pointers:
- within the bounds of an array
- one past the last element of an array
but nothing about a pointer one element before the first element of an
array.
Thoughts?
Index: history.c
===================================================================
RCS file: /d/cvs/src/bin/ksh/history.c,v
retrieving revision 1.69
diff -u -p -p -u -r1.69 history.c
--- history.c 30 Aug 2017 17:08:45 -0000 1.69
+++ history.c 31 Aug 2017 12:01:48 -0000
@@ -39,6 +39,7 @@ static char **hist_get_oldest(void);
static void histbackup(void);
static FILE *histfh;
+static char **histbase; /* actual start of the history[] allocation */
static char **current; /* current position in history[] */
static char *hname; /* current name of history file */
static int hstarted; /* set after hist_init() called */
@@ -557,8 +558,9 @@ sethistsize(int n)
memmove(history, histptr - offset, n * sizeof(char *));
}
- history = areallocarray(history, n, sizeof(char *), APERM);
histsize = n;
+ histbase = areallocarray(histbase, n + 1, sizeof(char *),
APERM);
+ history = histbase + 1;
histptr = history + offset;
}
}
@@ -597,9 +599,15 @@ sethistfile(const char *name)
void
init_histvec(void)
{
- if (history == NULL) {
+ if (histbase == NULL) {
histsize = HISTORYSIZE;
- history = areallocarray(NULL, histsize, sizeof(char *), APERM);
+ /*
+ * allocate one extra element so that histptr always
+ * lays within array bounds
+ */
+ histbase = areallocarray(NULL, histsize + 1, sizeof(char *),
+ APERM);
+ history = histbase + 1;
histptr = history - 1;
}
}
--
jca | PGP : 0x1524E7EE / 5135 92C1 AD36 5293 2BDF DDCC 0DFA 74AE 1524 E7EE
