From: Denys Vlasenko <dvlasenk@redhat.com>
Date: Wed, 24 Aug 2011 23:13:43 +0000 (+0200)
Subject: Opotimize "scno >= 0 && scno < nsyscalls" check
X-Git-Tag: v4.7~287
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=cb6f056004a10d5c3ed0341366e3ddeb53cac5e6;p=strace

Opotimize "scno >= 0 && scno < nsyscalls" check

gcc can't figure out on its own that this check can be done with
single compare, and does two compares. We can help it by casting
scno to unsigned long: ((unsigned long)(scno) < nsyscalls)

* defs.h: New macro SCNO_IN_RANGE(long_var).
* count.c (count_syscall): Use SCNO_IN_RANGE() instead of open-coded check.
* syscall.c (getrval2): Use SCNO_IN_RANGE() instead of open-coded check.
This fixes a bug: missing check for scno < 0 and scno > nsyscalls
instead of scno >= nsyscalls.
(get_scno): Use SCNO_IN_RANGE() instead of open-coded check.
This fixes a bug: scno > nsyscalls instead of scno >= nsyscalls.
(known_scno): Use SCNO_IN_RANGE() instead of open-coded check.
(internal_syscall): Likewise.
(syscall_enter): Likewise.
(trace_syscall_entering): Likewise.
(get_error): Likewise.
(trace_syscall_exiting): Likewise.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
---

diff --git a/count.c b/count.c
index 86b19531..77fc919d 100644
--- a/count.c
+++ b/count.c
@@ -50,7 +50,7 @@ static struct timeval shortest = { 1000000, 0 };
 void
 count_syscall(struct tcb *tcp, struct timeval *tv)
 {
-	if (tcp->scno < 0 || tcp->scno >= nsyscalls)
+	if (!SCNO_IN_RANGE(tcp->scno))
 		return;
 
 	if (!counts) {
diff --git a/defs.h b/defs.h
index a6b2da71..d0cb058f 100644
--- a/defs.h
+++ b/defs.h
@@ -728,6 +728,8 @@ extern unsigned nioctlents;
 extern const char *const *signalent;
 extern unsigned nsignals;
 
+#define SCNO_IN_RANGE(scno) ((unsigned long)(scno) < nsyscalls)
+
 #if HAVE_LONG_LONG
 
 /* _l refers to the lower numbered u_arg,
diff --git a/syscall.c b/syscall.c
index 5a09b315..a04b0041 100644
--- a/syscall.c
+++ b/syscall.c
@@ -675,11 +675,12 @@ getrval2(struct tcb *tcp)
 int
 sys_indir(struct tcb *tcp)
 {
-	int i, scno, nargs;
+	int i, nargs;
+	long scno;
 
 	if (entering(tcp)) {
 		scno = tcp->u_arg[0];
-		if (scno > nsyscalls) {
+		if (!SCNO_IN_RANGE(scno)) {
 			fprintf(stderr, "Bogus syscall: %u\n", scno);
 			return 0;
 		}
@@ -1045,7 +1046,7 @@ get_scno(struct tcb *tcp)
 	r2 = regs[REG_V0];
 
 	scno = r2;
-	if (scno < 0 || scno > nsyscalls) {
+	if (!SCNO_IN_RANGE(scno)) {
 		if (a3 == 0 || a3 == -1) {
 			if (debug)
 				fprintf(stderr, "stray syscall exit: v0 = %ld\n", scno);
@@ -1058,7 +1059,7 @@ get_scno(struct tcb *tcp)
 	if (upeek(tcp, REG_V0, &scno) < 0)
 		return -1;
 
-	if (scno < 0 || scno > nsyscalls) {
+	if (!SCNO_IN_RANGE(scno)) {
 		if (a3 == 0 || a3 == -1) {
 			if (debug)
 				fprintf(stderr, "stray syscall exit: v0 = %ld\n", scno);
@@ -1075,7 +1076,7 @@ get_scno(struct tcb *tcp)
 	 * Do some sanity checks to figure out if it's
 	 * really a syscall entry
 	 */
-	if (scno < 0 || scno > nsyscalls) {
+	if (!SCNO_IN_RANGE(scno)) {
 		if (a3 == 0 || a3 == -1) {
 			if (debug)
 				fprintf(stderr, "stray syscall exit: r0 = %ld\n", scno);
@@ -1228,7 +1229,7 @@ known_scno(struct tcb *tcp)
 {
 	long scno = tcp->scno;
 #if SUPPORTED_PERSONALITIES > 1
-	if (scno >= 0 && scno < nsyscalls && sysent[scno].native_scno != 0)
+	if (SCNO_IN_RANGE(scno) && sysent[scno].native_scno != 0)
 		scno = sysent[scno].native_scno;
 	else
 #endif
@@ -1425,7 +1426,7 @@ internal_syscall(struct tcb *tcp)
 	 */
 	int (*func)();
 
-	if (tcp->scno < 0 || tcp->scno >= nsyscalls)
+	if (!SCNO_IN_RANGE(tcp->scno))
 		return 0;
 
 	func = sysent[tcp->scno].sys_func;
@@ -1464,7 +1465,7 @@ syscall_enter(struct tcb *tcp)
 #ifdef LINUX
 	int i, nargs;
 
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls)
+	if (SCNO_IN_RANGE(tcp->scno))
 		nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
 		nargs = tcp->u_nargs = MAX_ARGS;
@@ -1635,7 +1636,7 @@ syscall_enter(struct tcb *tcp)
 #endif /* LINUX */
 #ifdef SUNOS4
 	int i, nargs;
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls)
+	if (SCNO_IN_RANGE(tcp->scno))
 		nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
 		nargs = tcp->u_nargs = MAX_ARGS;
@@ -1653,7 +1654,7 @@ syscall_enter(struct tcb *tcp)
 	 * SGI is broken: even though it has pr_sysarg, it doesn't
 	 * set them on system call entry.  Get a clue.
 	 */
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls)
+	if (SCNO_IN_RANGE(tcp->scno))
 		tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
 		tcp->u_nargs = tcp->status.pr_nsysarg;
@@ -1671,7 +1672,7 @@ syscall_enter(struct tcb *tcp)
 	/*
 	 * Like SGI, UnixWare doesn't set pr_sysarg until system call exit
 	 */
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls)
+	if (SCNO_IN_RANGE(tcp->scno))
 		tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
 		tcp->u_nargs = tcp->status.pr_lwp.pr_nsysarg;
@@ -1679,14 +1680,14 @@ syscall_enter(struct tcb *tcp)
 		tcp->u_nargs * sizeof(tcp->u_arg[0]), (char *) tcp->u_arg);
 # elif defined(HAVE_PR_SYSCALL)
 	int i;
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls)
+	if (SCNO_IN_RANGE(tcp->scno))
 		tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
 		tcp->u_nargs = tcp->status.pr_nsysarg;
 	for (i = 0; i < tcp->u_nargs; i++)
 		tcp->u_arg[i] = tcp->status.pr_sysarg[i];
 # elif defined(I386)
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls)
+	if (SCNO_IN_RANGE(tcp->scno))
 		tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
 		tcp->u_nargs = 5;
@@ -1698,7 +1699,7 @@ syscall_enter(struct tcb *tcp)
 # endif
 #endif /* SVR4 */
 #ifdef FREEBSD
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls &&
+	if (SCNO_IN_RANGE(tcp->scno) &&
 	    sysent[tcp->scno].nargs > tcp->status.val)
 		tcp->u_nargs = sysent[tcp->scno].nargs;
 	else
@@ -1756,7 +1757,7 @@ trace_syscall_entering(struct tcb *tcp)
 		tcp_last = tcp;
 		if (scno_good != 1)
 			tprintf("????" /* anti-trigraph gap */ "(");
-		else if (tcp->scno >= nsyscalls || tcp->scno < 0)
+		else if (!SCNO_IN_RANGE(tcp->scno))
 			tprintf("syscall_%lu(", tcp->scno);
 		else
 			tprintf("%s(", sysent[tcp->scno].sys_name);
@@ -1857,7 +1858,7 @@ trace_syscall_entering(struct tcb *tcp)
 
 	internal_syscall(tcp);
 
-	if ((tcp->scno >= 0 && tcp->scno < nsyscalls &&
+	if ((SCNO_IN_RANGE(tcp->scno) &&
 	     !(qual_flags[tcp->scno] & QUAL_TRACE)) ||
 	    (tracing_paths && !pathtrace_match(tcp))) {
 		tcp->flags |= TCB_INSYSCALL | TCB_FILTERED;
@@ -1874,11 +1875,11 @@ trace_syscall_entering(struct tcb *tcp)
 	printleader(tcp);
 	tcp->flags &= ~TCB_REPRINT;
 	tcp_last = tcp;
-	if (tcp->scno >= nsyscalls || tcp->scno < 0)
+	if (!SCNO_IN_RANGE(tcp->scno))
 		tprintf("syscall_%lu(", tcp->scno);
 	else
 		tprintf("%s(", sysent[tcp->scno].sys_name);
-	if (tcp->scno >= nsyscalls || tcp->scno < 0 ||
+	if (!SCNO_IN_RANGE(tcp->scno) ||
 	    ((qual_flags[tcp->scno] & QUAL_RAW) &&
 	     sysent[tcp->scno].sys_func != sys_exit))
 		res = printargs(tcp);
@@ -2011,7 +2012,7 @@ get_error(struct tcb *tcp)
 	int u_error = 0;
 #ifdef LINUX
 	int check_errno = 1;
-	if (tcp->scno >= 0 && tcp->scno < nsyscalls &&
+	if (SCNO_IN_RANGE(tcp->scno) &&
 	    sysent[tcp->scno].sys_flags & SYSCALL_NEVER_FAILS) {
 		check_errno = 0;
 	}
@@ -2257,7 +2258,7 @@ dumpio(struct tcb *tcp)
 		return;
 	if (tcp->u_arg[0] < 0 || tcp->u_arg[0] >= MAX_QUALS)
 		return;
-	if (tcp->scno < 0 || tcp->scno >= nsyscalls)
+	if (!SCNO_IN_RANGE(tcp->scno))
 		return;
 	if (sysent[tcp->scno].sys_func == printargs)
 		return;
@@ -2317,7 +2318,7 @@ trace_syscall_exiting(struct tcb *tcp)
 
 	if (tcp->flags & TCB_REPRINT) {
 		printleader(tcp);
-		if (tcp->scno >= nsyscalls || tcp->scno < 0)
+		if (!SCNO_IN_RANGE(tcp->scno))
 			tprintf("<... syscall_%lu resumed> ", tcp->scno);
 		else
 			tprintf("<... %s resumed> ", sysent[tcp->scno].sys_name);
@@ -2340,7 +2341,7 @@ trace_syscall_exiting(struct tcb *tcp)
 		return res;
 	}
 
-	if (tcp->scno >= nsyscalls || tcp->scno < 0
+	if (!SCNO_IN_RANGE(tcp->scno)
 	    || (qual_flags[tcp->scno] & QUAL_RAW))
 		sys_res = printargs(tcp);
 	else {
@@ -2360,7 +2361,7 @@ trace_syscall_exiting(struct tcb *tcp)
 	tprintf(") ");
 	tabto(acolumn);
 	u_error = tcp->u_error;
-	if (tcp->scno >= nsyscalls || tcp->scno < 0 ||
+	if (!SCNO_IN_RANGE(tcp->scno) ||
 	    qual_flags[tcp->scno] & QUAL_RAW) {
 		if (u_error)
 			tprintf("= -1 (errno %ld)", u_error);