xspawn: Work around a NetBSD posix_spawn() bug

NetBSD's posix_spawn() surprisingly has the same bug as its
posix_spawnp(): the executable is resolved before the file actions.
Detect this case and work around it by falling back to fork()/exec() if
we need to.

2 files changed, 29 insertions, 13 deletions

diff --git a/src/xspawn.c b/src/xspawn.c
index 7fa16b7..7ead45a 100644
--- a/src/xspawn.c
+++ b/src/xspawn.c
@@ -232,6 +232,11 @@ int bfs_spawn_adddup2(struct bfs_spawn *ctx, int oldfd, int newfd) {
  */
 #define BFS_POSIX_SPAWNP_AFTER_FCHDIR !(__APPLE__ || __NetBSD__)
 
+/**
+ * NetBSD even resolves the executable before file actions with posix_spawn()!
+ */
+#define BFS_POSIX_SPAWN_AFTER_FCHDIR !__NetBSD__
+
 int bfs_spawn_addfchdir(struct bfs_spawn *ctx, int fd) {
 	struct bfs_spawn_action *action = bfs_spawn_action(BFS_SPAWN_FCHDIR);
 	if (!action) {
@@ -553,6 +558,12 @@ static bool bfs_use_posix_spawn(const struct bfs_resolver *res, const struct bfs
 	}
 #endif
 
+#if !BFS_POSIX_SPAWN_AFTER_FCHDIR
+	if (res->exe[0] != '/' && bfs_spawn_will_chdir(ctx)) {
+		return false;
+	}
+#endif
+
 	return true;
 }
 
diff --git a/tests/xspawn.c b/tests/xspawn.c
index 0244006..6864192 100644
--- a/tests/xspawn.c
+++ b/tests/xspawn.c
@@ -99,6 +99,22 @@ static int reset_path(char *old_path) {
 	return ret;
 }
 
+/** Spawn the test binary and check for success. */
+static void check_spawnee(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) {
+	pid_t pid = bfs_spawn(exe, ctx, argv, envp);
+	if (!bfs_echeck(pid >= 0, "bfs_spawn('%s')", exe)) {
+		return;
+	}
+
+	int wstatus;
+	bool exited = bfs_echeck(xwaitpid(pid, &wstatus, 0) == pid)
+		&& bfs_check(WIFEXITED(wstatus));
+	if (exited) {
+		int wexit = WEXITSTATUS(wstatus);
+		bfs_check(wexit == EXIT_SUCCESS, "xspawnee: exit(%d)", wexit);
+	}
+}
+
 /** Check that we resolve executables in $PATH correctly. */
 static void check_use_path(bool use_posix) {
 	struct bfs_spawn spawn;
@@ -133,20 +149,9 @@ static void check_use_path(bool use_posix) {
 	}
 
 	char *argv[] = {"xspawnee", old_path, NULL};
-	pid_t pid = bfs_spawn("xspawnee", &spawn, argv, envp);
-	if (!bfs_echeck(pid >= 0, "bfs_spawn()")) {
-		goto path;
-	}
-
-	int wstatus;
-	bool exited = bfs_echeck(xwaitpid(pid, &wstatus, 0) == pid)
-		&& bfs_check(WIFEXITED(wstatus));
-	if (exited) {
-		int wexit = WEXITSTATUS(wstatus);
-		bfs_check(wexit == EXIT_SUCCESS, "xspawnee: exit(%d)", wexit);
-	}
+	check_spawnee("xspawnee", &spawn, argv, envp);
+	check_spawnee("tests/xspawnee", &spawn, argv, envp);
 
-path:
 	bfs_echeck(reset_path(old_path) == 0);
 env:
 	for (char **var = envp; *var; ++var) {