proc_open: Use posix_spawn(3) interface on systems where it is profitable

As the size of the PHP process increases, forking gets slower and memory
consumption increases, degrading the performance in varying degrees.

This patch makes proc_open use posix_spawn only on systems which is known to be
safe, faster than the HAVE_FORK path and have posix_spawn_file_actions_addchdir_np(3)
action.
Non scientific benchmark shows running php own's test suite on linux completes
dozens of seconds faster, the impact is probably higher on systems where
posix_spawn is a syscall.

Author: crrodriguez

ext/standard/config.m4

@@ -376,6 +376,8 @@ dnl
 
 PHP_CHECK_FUNC(res_search, resolv, bind, socket)
 
+PHP_CHECK_FUNC(posix_spawn_file_actions_addchdir_np)
+
 dnl
 dnl Check for strptime()
 dnl

ext/standard/proc_open.c

@@ -36,6 +36,18 @@
 #include <fcntl.h>
 #endif
 
+#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP
+/* Only defined on glibc >= 2.29, FreeBSD CURRENT, musl >= 1.1.24,
+ * MacOS Catalina or later..
+ * It should be posible to modify this so it is also
+ * used in older systems when $cwd == NULL but care must be taken
+ * as at least glibc < 2.24 has a legacy implementation known
+ * to be really buggy.
+ */
+#include <spawn.h>
+#define USE_POSIX_SPAWN
+#endif
+
 /* This symbol is defined in ext/standard/config.m4.
  * Essentially, it is set if you HAVE_FORK || PHP_WIN32
  * Other platforms may modify that configure check and add suitable #ifdefs
@@ -982,6 +994,36 @@ static zend_result set_proc_descriptor_from_resource(zval *resource, descriptors
 }
 
 #ifndef PHP_WIN32
+#if defined(USE_POSIX_SPAWN)
+static zend_result close_parentends_of_pipes(posix_spawn_file_actions_t * actions, descriptorspec_item *descriptors, int ndesc)
+{
+	int r;
+	for (int i = 0; i < ndesc; i++) {
+		if (descriptors[i].type != DESCRIPTOR_TYPE_STD) {
+			r = posix_spawn_file_actions_addclose(actions, descriptors[i].parentend);
+			if (r != 0) {
+				php_error_docref(NULL, E_WARNING, "Cannot close file descriptor %d: %s", descriptors[i].parentend, strerror(r));
+				return FAILURE;
+			}
+		}
+		if (descriptors[i].childend != descriptors[i].index) {
+			r = posix_spawn_file_actions_adddup2(actions, descriptors[i].childend, descriptors[i].index);
+			if (r != 0) {
+				php_error_docref(NULL, E_WARNING, "Unable to copy file descriptor %d (for pipe) into "
+						"file descriptor %d: %s", descriptors[i].childend, descriptors[i].index, strerror(r));
+				return FAILURE;
+			}
+			r = posix_spawn_file_actions_addclose(actions, descriptors[i].childend);
+			if (r != 0) {
+				php_error_docref(NULL, E_WARNING, "Cannot close file descriptor %d: %s", descriptors[i].childend, strerror(r));
+				return FAILURE;
+			}
+		}
+	}
+
+	return SUCCESS;
+}
+#else
 static zend_result close_parentends_of_pipes(descriptorspec_item *descriptors, int ndesc)
 {
 	/* We are running in child process
@@ -1005,6 +1047,7 @@ static zend_result close_parentends_of_pipes(descriptorspec_item *descriptors, i
 	return SUCCESS;
 }
 #endif
+#endif
 
 static void close_all_descriptors(descriptorspec_item *descriptors, int ndesc)
 {
@@ -1216,6 +1259,37 @@ PHP_FUNCTION(proc_open)
 	childHandle = pi.hProcess;
 	child       = pi.dwProcessId;
 	CloseHandle(pi.hThread);
+#elif defined(USE_POSIX_SPAWN)
+	posix_spawn_file_actions_t factions;
+	int r;
+	posix_spawn_file_actions_init(&factions);
+
+	if (close_parentends_of_pipes(&factions, descriptors, ndesc) == FAILURE) {
+		posix_spawn_file_actions_destroy(&factions);
+		close_all_descriptors(descriptors, ndesc);
+		goto exit_fail;
+	}
+
+	if (cwd) {
+		r = posix_spawn_file_actions_addchdir_np(&factions, cwd);
+		if (r != 0) {
+			php_error_docref(NULL, E_WARNING, "posix_spawn_file_actions_addchdir_np() failed: %s", strerror(r));
+		}
+	}
+
+	if (argv) {
+		r = posix_spawnp(&child, ZSTR_VAL(command_str), &factions, NULL, argv, (env.envarray ? env.envarray : environ));
+	} else {
+		r = posix_spawn(&child, "/bin/sh" , &factions, NULL,
+				(char * const[]) {"sh", "-c", ZSTR_VAL(command_str), NULL},
+				env.envarray ? env.envarray : environ);
+	}
+	posix_spawn_file_actions_destroy(&factions);
+	if (r != 0) {
+		close_all_descriptors(descriptors, ndesc);
+		php_error_docref(NULL, E_WARNING, "posix_spawn() failed: %s", strerror(r));
+		goto exit_fail;
+	}
 #elif HAVE_FORK
 	/* the Unix way */
 	child = fork();