Allow SA_RESTART for SIGALRM

If no explicit restart_syscalls is passed, default to
restart_syscalls=0 for SIGALRM only, to reduce BC impact.

Author: nikic

NEWS

@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 7.4.0RC4
 
+- Pcntl:
+  . Fixed bug #77335 (PHP is preventing SIGALRM from specifying SA_RESTART).
+    (Nikita)
+
 - SimpleXML:
   . Fixed bug #75245 (Don't set content of elements with only whitespaces). 
     (eriklundin)

UPGRADING

@@ -82,6 +82,11 @@ PHP 7.4 UPGRADE NOTES
     function does not throw, so explicitly checking it is not necessary.
     RFC: http://php.net/manual/de/function.openssl-random-pseudo-bytes.php
 
+- Pcntl:
+  . The $restart_syscalls flag for pcntl_signal() will now be respected for
+    SIGALARM. Previously it was hardcoded to false. To reduce the backwards
+    compatibility impact, the default for SIGALARM will remain false however.
+
 - PCRE:
   . When PREG_UNMATCHED_AS_NULL mode is used, trailing unmatched capturing
     groups will now also be set to null (or [null, -1] if offset capture is

ext/pcntl/pcntl.c

@@ -1057,8 +1057,9 @@ PHP_FUNCTION(pcntl_signal)
 	zval *handle;
 	zend_long signo;
 	zend_bool restart_syscalls = 1;
+	zend_bool restart_syscalls_is_null = 1;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "lz|b", &signo, &handle, &restart_syscalls) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "lz|b!", &signo, &handle, &restart_syscalls, &restart_syscalls_is_null) == FAILURE) {
 		return;
 	}
 
@@ -1080,6 +1081,13 @@ PHP_FUNCTION(pcntl_signal)
 		}
 	}
 
+	/* If restart_syscalls was not explicitly specified and the signal is SIGALRM, then default
+	 * restart_syscalls to false. PHP used to enforce that restart_syscalls is false for SIGALRM,
+	 * so we keep this differing default to reduce the degree of BC breakage. */
+	if (restart_syscalls_is_null && signo == SIGALRM) {
+		restart_syscalls = 0;
+	}
+
 	/* Special long value case for SIG_DFL and SIG_IGN */
 	if (Z_TYPE_P(handle) == IS_LONG) {
 		if (Z_LVAL_P(handle) != (zend_long) SIG_DFL && Z_LVAL_P(handle) != (zend_long) SIG_IGN) {

ext/pcntl/php_signal.c

@@ -41,7 +41,7 @@ Sigfunc *php_signal4(int signo, Sigfunc *func, int restart, int mask_all)
 #ifdef HAVE_STRUCT_SIGINFO_T
 	act.sa_flags |= SA_SIGINFO;
 #endif
-	if (signo == SIGALRM || (! restart)) {
+	if (!restart) {
 #ifdef SA_INTERRUPT
 		act.sa_flags |= SA_INTERRUPT; /* SunOS */
 #endif