ash: use alloca to get rid of setjmp

Now that the only thing protected by setjmp/longjmp is the saved string,
we can allocate it on the stack to get rid of the jump.

Based on commit bd35d8e from git://git.kernel.org/pub/scm/utils/dash/dash.git
by Herbert Xu.

function                                             old     new   delta
readtoken1                                          3182    3116     -66
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-66)             Total: -66 bytes

Signed-off-by: Ron Yorston <rmy@frippery.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 2 insertions, 34 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 6627cec9b..f4779ee2b 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -11132,19 +11132,6 @@ readtoken1(int c, int syntax, char *eofmark, int striptabs)
 
         IF_ASH_BASH_COMPAT(smallint bash_dollar_squote = 0;)
 
-#if __GNUC__
-        /* Avoid longjmp clobbering */
-        (void) &out;
-        (void) &quotef;
-        (void) &dblquote;
-        (void) &varnest;
-        (void) &arinest;
-        (void) &parenlevel;
-        (void) &dqvarnest;
-        (void) &oldstyle;
-        (void) &prevsyntax;
-        (void) &syntax;
-#endif
         startlinno = g_parsefile->linno;
         bqlist = NULL;
         quotef = 0;
@@ -11609,30 +11596,16 @@ parsesub: {
 parsebackq: {
         struct nodelist **nlpp;
         union node *n;
-        char *volatile str;
-        struct jmploc jmploc;
-        struct jmploc *volatile savehandler;
+        char *str;
         size_t savelen;
         smallint saveprompt = 0;
 
-#ifdef __GNUC__
-        (void) &saveprompt;
-#endif
-        if (setjmp(jmploc.loc)) {
-                free(str);
-                exception_handler = savehandler;
-                longjmp(exception_handler->loc, 1);
-        }
-        INT_OFF;
         str = NULL;
         savelen = out - (char *)stackblock();
         if (savelen > 0) {
-                str = ckmalloc(savelen);
+                str = alloca(savelen);
                 memcpy(str, stackblock(), savelen);
         }
-        savehandler = exception_handler;
-        exception_handler = &jmploc;
-        INT_ON;
         if (oldstyle) {
                 /* We must read until the closing backquote, giving special
                  * treatment to some slashes, and then push the string and
@@ -11731,12 +11704,7 @@ parsebackq: {
         if (str) {
                 memcpy(out, str, savelen);
                 STADJUST(savelen, out);
-                INT_OFF;
-                free(str);
-                str = NULL;
-                INT_ON;
         }
-        exception_handler = savehandler;
         USTPUTC(CTLBACKQ, out);
         if (oldstyle)
                 goto parsebackq_oldreturn;