nuttx/libs/libc/libc.csv at a229e8b87e7123d2d16029b56a2de99ef1b80eef

mirror of https://github.com/apache/nuttx.git synced 2026-08-01 20:28:58 +00:00

Marco Casaroli a229e8b87e sched/arch/libc: give fork(), vfork() and task_fork() separate semantics

NuttX implemented fork() and vfork() as the same function.  Both were libc
wrappers around a single up_fork() syscall; vfork() differed only by a
trailing waitpid().  Underneath, the child joined the parent's address
environment -- the same addrenv_join() that pthread_create() uses -- and got
a private copy of the stack.  So the child shared .data, .bss and the heap
with its parent and ran concurrently with it.

That is not fork().  It is vfork()-with-a-private-stack under fork()'s name,
and the history says so: today's fork() is NuttX's old vfork(), renamed in
c33d1c9c97 (2023) without any change of behaviour.  The failure was silent --
a program written against POSIX fork() compiled, ran, and had its child's
writes land in the parent's variables.

Separate them into three primitives, chosen by which function the caller
called rather than by what the hardware happens to be:

  fork()       child gets its own copy of the parent's memory at the same
               virtual addresses; runs concurrently.  Only where an address
               environment can be duplicated -- elsewhere it is not declared
               at all, so calling it is a build error naming the function.
  vfork()      child shares the parent's memory; parent suspended until the
               child _exit()s or exec()s.  Implementable everywhere.
  task_fork()  the historical behaviour under an honest name: shares memory,
               private stack copy, both running.  Non-POSIX, in sched.h.

Below libc there are now three syscalls -- up_task_fork(), up_vfork() and
up_fork().  The per-arch register snapshot is common to all three; each
architecture's entry points share one sequence and differ only in a
FORK_TYPE_* selector (include/nuttx/fork.h) handed to nxtask_setup_fork(),
which is the single place the memory semantics are decided.

The vfork() parent suspension moves out of libc into nxtask_start_vfork(),
released from nxsched_release_tcb().  Two things follow: the parent is
resumed at exec(), since exec_swap() has already handed the child's pid to
the loaded program by the time the vfork stub exits, and vfork() no longer
depends on CONFIG_SCHED_WAITPID.

Releasing there requires one fix in nxtask_exit().  It raises rtcb->lockcount
directly rather than through sched_lock() while it tears the TCB down, so the
nxsem_post() that wakes the vfork() parent queues it on g_pendingtasks -- and
the matching raw lockcount-- does not merge that list the way sched_unlock()
would, leaving the parent stranded with nothing left to move it off.  A
nxsched_merge_pending() after the decrement publishes it.  The call is a
no-op while pre-emption is still disabled, and up_exit() re-reads this_task()
afterwards, so a change of the ready-to-run head is honoured.  Without it
vfork() deadlocks on any configuration where no other task happens to call
sched_unlock() afterwards -- rv-virt:nsh64 and rv-virt:pnsh64, for instance,
where NSH is blocked in waitpid() holding the lock.

fork() is built on a new addrenv_fork(), backed by an up_addrenv_fork() hook
that duplicates an address environment into freshly allocated pages mapped at
the same virtual addresses -- unlike up_addrenv_clone(), which copies only
the representation and leaves both pointing at the same page tables.  The
child then adopts the parent's stack geometry rather than being given a
relocated copy: a pointer to a stack local taken before fork() must name the
same object in the child that it named in the parent, and the parent's stack
is already in the duplicate, with its contents, at the parent's address.

No architecture implements up_addrenv_fork() yet, so this commit leaves
fork() unavailable everywhere.  That is the intended state.  It withdraws
fork() from ARCH_ARM, flat ARCH_ARM64, ARCH_RISCV, ARCH_SIM and ARCH_X86_64,
where until now it named the sharing primitive; per-architecture patches
restore it, with POSIX semantics, as up_addrenv_fork() lands.  Nothing is
lost in the meantime: task_fork() is that same sharing primitive under its
own name, and CONFIG_FORK_IS_TASK_FORK (default n) aliases fork() back to it
for legacy code, on exactly the configurations that had fork() before.

Kconfig: ARCH_HAVE_TASK_FORK and ARCH_HAVE_VFORK inherit ARCH_HAVE_FORK's
select lines, conditions included, so no configuration gains machinery;
ARCH_HAVE_FORK is redefined to mean "can provide POSIX fork() semantics" and
derives from the new ARCH_HAVE_ADDRENV_FORK.

There is one deliberate departure from "verbatim".  ARCH_ARM selected the
fork family unconditionally, BUILD_KERNEL included, and that has never
worked:  on a kernel build the architecture's fork entry point sees the
kernel's return address and stack pointer rather than the caller's, so the
child resumes at a kernel address.  On qemu-armv7a:knsh master faults in
ostest's task_fork case with "Child did not run" and then a data abort;
without the condition this change faults the same way through vfork().
ARCH_ARM64 and ARCH_X86_64 already carried "if !BUILD_KERNEL" for exactly
this reason -- ARM was the outlier.  Conditioning it turns a runtime fault
into an honest absence, which is the whole point of the change; arch/arm
takes the condition off again in the patch that adds its saved-syscall-frame
path.  Only the MMU-capable ARM ports are affected, since Cortex-M cannot
build BUILD_KERNEL at all.

Also fixes two latent syntax errors found on the way: a missing comma in
riscv_fork.c and mips_fork.c, both in *_FRAMEPOINTER && !SAVE_GP branches
that are never compiled today.

Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>

Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

2026-07-29 16:39:07 +02:00

30 KiB

Raw Blame History

1	__assert	assert.h		void	FAR const char *	int	FAR const char *
2	__cxa_atexit	stdlib.h		int	FAR CODE void ()(FAR void )\|FAR void *	FAR void *	FAR void *
3	aio_suspend	aio.h	defined(CONFIG_FS_AIO)	int	FAR const struct aiocb * const []\|FAR const struct aiocb * const *	int	FAR const struct timespec *
4	asprintf	stdio.h		int	FAR char **	FAR const IPTR char *	...
5	crc32part	nuttx/crc32.h		uint32_t	FAR const uint8_t *	size_t	uint32_t
6	dq_addafter	nuttx/queue.h		void	FAR dq_entry_t *	FAR dq_entry_t *	FAR dq_queue_t *
7	fgets	stdio.h	defined(CONFIG_FILE_STREAM)	FAR char *	FAR char *	int	FAR FILE *
8	fnmatch	fnmatch.h		int	FAR const char *	FAR const char *	int
9	fprintf	stdio.h	defined(CONFIG_FILE_STREAM)	int	FAR FILE *	FAR const IPTR char *	...
10	fscanf	stdio.h		int	FAR FILE *	FAR const char *	...
11	fseek	stdio.h	defined(CONFIG_FILE_STREAM)	int	FAR FILE *	long int	int
12	getopt	unistd.h		int	int	FAR char * const []\|FAR char * const *	FAR const char *
13	getrandom	sys/random.h	!defined(CONFIG_BUILD_KERNEL)	ssize_t	FAR void *	size_t	unsigned int
14	inet_pton	arpa/inet.h		int	int	FAR const char *	FAR void *
15	lib_dumpbuffer	debug.h		void	FAR const char *	FAR const uint8_t *	unsigned int
16	mbrlen	wchar.h		size_t	FAR const char *	size_t	FAR mbstate_t *
17	mbstowcs	stdlib.h		size_t	FAR wchar_t *	FAR const char *	size_t
18	mbtowc	stdlib.h		int	FAR wchar_t *	FAR const char *	size_t
19	memchr	string.h		FAR void *	FAR const void *	int	size_t
20	memcmp	string.h		int	FAR const void *	FAR const void *	size_t
21	memcpy	string.h		FAR void *	FAR void *	FAR const void *	size_t
22	memmove	string.h		FAR void *	FAR void *	FAR const void *	size_t
23	memset	string.h		FAR void *	FAR void *	int	size_t
24	posix_fallocate	fcntl.h		int	int	off_t	off_t
25	posix_memalign	stdlib.h		int	FAR void **	size_t	size_t
26	pthread_barrier_init	pthread.h	!defined(CONFIG_DISABLE_PTHREAD)	int	FAR pthread_barrier_t *	FAR const pthread_barrierattr_t *	unsigned int
27	pthread_cond_timedwait	pthread.h	!defined(CONFIG_DISABLE_PTHREAD)	int	FAR pthread_cond_t *	FAR pthread_mutex_t *	FAR const struct timespec *
28	pthread_getname_np	pthread.h	!defined(CONFIG_DISABLE_PTHREAD)	int	pthread_t	char *	size_t
29	pthread_mutex_setprioceiling	pthread.h	!defined(CONFIG_DISABLE_PTHREAD) && defined(CONFIG_PRIORITY_PROTECT)	int	FAR pthread_mutex_t *	int	FAR int *
30	readdir_r	dirent.h		int	FAR DIR *	FAR struct dirent *	FAR struct dirent **
31	readv	sys/uio.h		ssize_t	int	FAR const struct iovec *	int
32	sem_init	semaphore.h		int	FAR sem_t *	int	unsigned int
33	setpriority	sys/resource.h		int	int	id_t	int
34	sprintf	stdio.h		int	FAR char *	FAR const IPTR char *	...
35	sprintf	stdio.h		int	FAR char *	FAR const IPTR char *	...
36	sq_addafter	nuttx/queue.h		void	FAR sq_entry_t *	FAR sq_entry_t *	FAR sq_queue_t *
37	sscanf	stdio.h		int	FAR const IPTR char *	FAR const char *	...
38	sscanf	stdio.h		int	FAR const char *	FAR const char *	...
39	strerror_r	string.h		int	int	FAR char *	size_t
40	strlcpy	string.h		size_t	FAR char *	FAR const char *	size_t
41	strncasecmp	strings.h		int	FAR const char *	FAR const char *	size_t
42	strncat	string.h		FAR char *	FAR char *	FAR const char *	size_t
43	strncmp	string.h		int	FAR const char *	FAR const char *	size_t
44	strncpy	string.h		FAR char *	FAR char *	FAR const char *	size_t
45	strtoimax	inttypes.h		intmax_t	FAR const char *	FAR char **	int
46	strtok_r	string.h		FAR char *	FAR char *	FAR const char *	FAR char **
47	strtol	stdlib.h		long	FAR const char *	FAR char **	int
48	strtoll	stdlib.h		long long	FAR const char *	FAR char **	int
49	strtoul	stdlib.h		unsigned long	FAR const char *	FAR char **	int
50	strtoull	stdlib.h		unsigned long long int	FAR const char *	FAR char **	int
51	strtoull	stdlib.h		unsigned long long	FAR const char *	FAR char **	int
52	strtoumax	inttypes.h		uintmax_t	FAR const char *	FAR char **	int
53	strxfrm	string.h	defined(CONFIG_LIBC_LOCALE)	size_t	FAR char *	FAR const char *	size_t
54	swab	unistd.h		void	FAR const void *	FAR void *	ssize_t
55	syslog	syslog.h		void	int	FAR const IPTR char *	...
56	tcsetattr	termios.h		int	int	int	FAR const struct termios *
57	vasprintf	stdio.h		int	FAR char **	FAR const IPTR char *	va_list
58	vfprintf	stdio.h	defined(CONFIG_FILE_STREAM)	int	FAR FILE *	FAR const IPTR char *	va_list
59	vsprintf	stdio.h		int	FAR char *	FAR const IPTR char *	va_list
60	vsscanf	stdio.h		int	FAR const char *	FAR const IPTR char *	va_list
61	vsyslog	syslog.h		void	int	FAR const IPTR char *	va_list
62	wcrtomb	wchar.h		size_t	FAR char *	wchar_t	FAR mbstate_t *
63	wcslcat	wchar.h		size_t	FAR wchar_t *	FAR const wchar_t *	size_t
64	wcsncat	wchar.h		FAR wchar_t *	FAR wchar_t *	FAR const wchar_t *	size_t
65	wcsncmp	wchar.h		int	FAR const wchar_t *	FAR const wchar_t *	size_t
66	wcsncpy	wchar.h		FAR wchar_t *	FAR wchar_t *	FAR const wchar_t *	size_t
67	wcslcpy	wchar.h		size_t	FAR wchar_t *	FAR const wchar_t *	size_t
68	wcstok	wchar.h		FAR wchar_t *	FAR wchar_t *	FAR const wchar_t *	FAR wchar_t **
69	wcstol	wchar.h		long int	FAR const wchar_t *	FAR wchar_t **	int
70	wcstoll	wchar.h		long long int	FAR const wchar_t *	FAR wchar_t **	int
71	wcstombs	stdlib.h		size_t	FAR char *	FAR const wchar_t *	size_t
72	wcstoul	wchar.h		unsigned long int	FAR const wchar_t *	FAR wchar_t **	int
73	wcsxfrm	wchar.h		size_t	FAR wchar_t *	FAR const wchar_t *	size_t
74	wmemchr	wchar.h		FAR wchar_t *	FAR const wchar_t *	wchar_t	size_t
75	wmemcmp	wchar.h		int	FAR const wchar_t *	FAR const wchar_t *	size_t
76	wmemcpy	wchar.h		FAR wchat_t *	FAR wchar_t *	FAR const wchar_t *	size_t
77	wmemmove	wchar.h		FAR wchat_t *	FAR wchar_t *	FAR const wchar_t *	size_t
78	wmemset	wchar.h		FAR wchat_t *	FAR wchar_t *	wchar_t	size_t
79	writev	sys/uio.h		ssize_t	int	FAR const struct iovec *	int

30 KiB Raw Blame History

30 KiB

Raw Blame History