Author: jilles
Date: Tue Dec 28 21:27:08 2010
New Revision: 216778
URL: http://svn.freebsd.org/changeset/base/216778
Log:
sh: Don't do optimized command substitution if expansions have side effects.
Before considering to execute a command substitution in the same process,
check if any of the expansions may have a side effect; if so, execute it in
a new process just like happens if it is not a single simple command.
Although the check happens at run time, it is a static check that does not
depend on current state. It is triggered by:
- expanding $! (which may cause the job to be remembered)
- ${var=value} default value assignment
- assignment operators in arithmetic
- parameter substitutions in arithmetic except ${#param}, $$, $# and $?
- command substitutions in arithmetic
This means that $((v+1)) does not prevent optimized command substitution,
whereas $(($v+1)) does, because $v might expand to something containing
assignment operators.
Scripts should not depend on these exact details for correctness. It is also
imaginable to have the shell fork if and when a side effect is encountered
or to create a new temporary namespace for variables.
Due to the $! change, the construct $(jobs $!) no longer works. The value of
$! should be stored in a variable outside command substitution first.
Added:
head/tools/regression/bin/sh/expansion/cmdsubst7.0 (contents, props changed)
Modified:
head/bin/sh/eval.c
head/bin/sh/expand.c
head/bin/sh/expand.h
Modified: head/bin/sh/eval.c
==============================================================================
--- head/bin/sh/eval.c Tue Dec 28 21:22:08 2010 (r216777)
+++ head/bin/sh/eval.c Tue Dec 28 21:27:08 2010 (r216778)
@@ -94,6 +94,7 @@ static void evalsubshell(union node *, i
static void evalredir(union node *, int);
static void expredir(union node *);
static void evalpipe(union node *);
+static int is_valid_fast_cmdsubst(union node *n);
static void evalcommand(union node *, int, struct backcmd *);
static void prehash(union node *);
@@ -565,6 +566,19 @@ evalpipe(union node *n)
+static int
+is_valid_fast_cmdsubst(union node *n)
+{
+ union node *argp;
+
+ if (n->type != NCMD)
+ return 0;
+ for (argp = n->ncmd.args ; argp ; argp = argp->narg.next)
+ if (expandhassideeffects(argp->narg.text))
+ return 0;
+ return 1;
+}
+
/*
* Execute a command inside back quotes. If it's a builtin command, we
* want to save its output in a block obtained from malloc. Otherwise
@@ -590,7 +604,7 @@ evalbackcmd(union node *n, struct backcm
exitstatus = 0;
goto out;
}
- if (n->type == NCMD) {
+ if (is_valid_fast_cmdsubst(n)) {
exitstatus = oexitstatus;
savehandler = handler;
if (setjmp(jmploc.loc)) {
Modified: head/bin/sh/expand.c
==============================================================================
--- head/bin/sh/expand.c Tue Dec 28 21:22:08 2010 (r216777)
+++ head/bin/sh/expand.c Tue Dec 28 21:27:08 2010 (r216778)
@@ -1570,6 +1570,78 @@ cvtnum(int num, char *buf)
}
/*
+ * Check statically if expanding a string may have side effects.
+ */
+int
+expandhassideeffects(const char *p)
+{
+ int c;
+ int arinest;
+
+ arinest = 0;
+ while ((c = *p++) != '\0') {
+ switch (c) {
+ case CTLESC:
+ p++;
+ break;
+ case CTLVAR:
+ c = *p++;
+ /* Expanding $! sets the job to remembered. */
+ if (*p == '!')
+ return 1;
+ if ((c & VSTYPE) == VSASSIGN)
+ return 1;
+ /*
+ * If we are in arithmetic, the parameter may contain
+ * '=' which may cause side effects. Exceptions are
+ * the length of a parameter and $$, $# and $? which
+ * are always numeric.
+ */
+ if ((c & VSTYPE) == VSLENGTH) {
+ while (*p != '=')
+ p++;
+ p++;
+ break;
+ }
+ if ((*p == '$' || *p == '#' || *p == '?') &&
+ p[1] == '=') {
+ p += 2;
+ break;
+ }
+ if (arinest > 0)
+ return 1;
+ break;
+ case CTLBACKQ:
+ case CTLBACKQ | CTLQUOTE:
+ if (arinest > 0)
+ return 1;
+ break;
+ case CTLARI:
+ arinest++;
+ break;
+ case CTLENDARI:
+ arinest--;
+ break;
+ case '=':
+ if (*p == '=') {
+ /* Allow '==' operator. */
+ p++;
+ continue;
+ }
+ if (arinest > 0)
+ return 1;
+ break;
+ case '!': case '<': case '>':
+ /* Allow '!=', '<=', '>=' operators. */
+ if (*p == '=')
+ p++;
+ break;
+ }
+ }
+ return 0;
+}
+
+/*
* Do most of the work for wordexp(3).
*/
Modified: head/bin/sh/expand.h
==============================================================================
--- head/bin/sh/expand.h Tue Dec 28 21:22:08 2010 (r216777)
+++ head/bin/sh/expand.h Tue Dec 28 21:27:08 2010 (r216778)
@@ -63,4 +63,5 @@ void expari(int);
int patmatch(const char *, const char *, int);
void rmescapes(char *);
int casematch(union node *, const char *);
+int expandhassideeffects(const char *);
int wordexpcmd(int, char **);
Added: head/tools/regression/bin/sh/expansion/cmdsubst7.0
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ head/tools/regression/bin/sh/expansion/cmdsubst7.0 Tue Dec 28 21:27:08
2010 (r216778)
@@ -0,0 +1,31 @@
+# $FreeBSD$
+
+failures=''
+ok=''
+
+testcase() {
+ code="$1"
+
+ unset v
+ eval ": \$($code)"
+
+ if [ "${v:+bad}" = "" ]; then
+ ok=x$ok
+ else
+ failures=x$failures
+ echo "Failure for $code"
+ fi
+}
+
+testcase ': ${v=0}'
+testcase ': ${v:=0}'
+testcase ': $((v=1))'
+testcase ': $((v+=1))'
+w='v=1'
+testcase ': $(($w))'
+testcase ': $((${$+v=1}))'
+testcase ': $((v${$+=1}))'
+testcase ': $((v $(echo =) 1))'
+testcase ': $(($(echo $w)))'
+
+test "x$failures" = x
_______________________________________________
svn-src-head@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
