rework mechanism for posix_spawnp calling posix_spawn

previously, a common __posix_spawnx backend was used that accepted an
additional argument for the execve variant to call in the child. this
moderately bloated up the posix_spawn function, shuffling arguments
between stack and/or registers to call a 7-argument function from a
6-argument one.

instead, tuck the exec function pointer in an unused part of the
(large) pthread_spawnattr_t structure, and have posix_spawnp duplicate
the attributes and fill in a pointer to __execvpe. the net code size
change is minimal, but the weight is shifted to the "heavier" function
which already pulls in more dependencies.

as a bonus, we get rid of an external symbol (__posix_spawnx) that had
no really good place for a declaration because it shouldn't have
existed to begin with.

1 files changed, 3 insertions, 1 deletions

diff --git a/include/spawn.h b/include/spawn.h
index bba57ce4..c9bd1939 100644
--- a/include/spawn.h
+++ b/include/spawn.h
@@ -28,7 +28,9 @@ typedef struct {
 	int __flags;
 	pid_t __pgrp;
 	sigset_t __def, __mask;
-	int __prio, __pol, __pad[16];
+	int __prio, __pol;
+	void *__fn;
+	char __pad[64-sizeof(void *)];
 } posix_spawnattr_t;
 
 typedef struct {