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 two 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.
Below libc there is still one syscall. up_fork() gains a bool saying which
primitive the caller used, since the per-architecture register snapshot is
the same for both, and passes it to nxtask_setup_fork(), which is the single
place the memory semantics are decided. The argument arrives in the first
argument register and is never touched: each architecture's snapshot takes
some other call-clobbered register for its scratch, so the flag is simply
still there when the C worker is called.
The vfork() parent suspension moves out of libc into nxtask_start_fork(),
released from nxsched_release_tcb() by nxtask_resume_vfork(). 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 leaves it queued where a blocked
task collects while pre-emption is off -- g_pendingtasks, or g_readytorun on
SMP -- and the matching raw lockcount-- does not publish it the way
sched_unlock() would, leaving the parent stranded with nothing to move it on.
The fix mirrors sched_unlock() for each case: nxsched_merge_pending(), or
nxsched_deliver_task() under CONFIG_SMP. Both are no-ops 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 wherever no
other task happens to call sched_unlock() afterwards -- rv-virt:nsh64 and
rv-virt:pnsh64, where NSH is blocked in waitpid() holding the lock, and
qemu-armv8a:citest_smp, which hangs the moment the vfork() test runs.
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. In the
meantime the sharing primitive is still there under the name that describes
it: vfork() for a child that runs a program, pthread_create() for a second
flow of control that shares memory, posix_spawn() for both at once.
Kconfig: ARCH_HAVE_VFORK inherits 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 now depends on ARCH_ADDRENV.
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 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.
BREAKING CHANGE: fork() is withdrawn from every architecture. It is no
longer declared in unistd.h, so code that calls it fails to build with an error
naming the function, and the sharing behaviour it used to have is gone rather
than renamed. CONFIG_ARCH_HAVE_FORK no longer means "fork() exists"; it means
"this configuration can provide POSIX fork() semantics", and no architecture
selects it yet.
Quick fix, chosen by why the call was made:
to run a program vfork() + exec*(), or better posix_spawn()
a second flow of control that pthread_create()
shares the caller's memory
a genuinely independent copy keep fork(), and wait for the per-arch patch
of the process that implements up_addrenv_fork() and selects
CONFIG_ARCH_HAVE_FORK
Out-of-tree code that tests CONFIG_ARCH_HAVE_FORK to decide whether a
fork-then-exec path is available wants CONFIG_ARCH_HAVE_VFORK instead, which is
selected in exactly the places CONFIG_ARCH_HAVE_FORK used to be. The full
migration guide is Documentation/guides/fork_vfork_migration.rst.
Assisted-by: Claude Code:claude-opus-5
Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
During the Toybox port to NuttX, Claude noticed that changes in the
menuconfig weren't taking affect. This issue exists for a long time on
NuttX, in fact BayLibre's presentation from 2017 make jokes about our
building system not been reliable:
https://www.youtube.com/watch?v=XUJK2htXxKw&t=320s
Stale archive members from $(AR)'s additive-only behavior can linger
after Kconfig toggles change which files provide a symbol, causing dead
weight or "multiple definition" link errors on incremental builds.
Fixed by splitting ARCHIVE into two macros: ARCHIVE keeps the original
additive behavior for apps/libapps.a, which many independent
subdirectories contribute to across a build, while the new
ARCHIVE_REBUILD deletes then archives for the far more common case
of a single Makefile building its own self-contained $(OBJS)
- all 39 such call sites now use it.
Assisted-By: Claude Sonnet 5
Signed-off-by: Alan C. Assis <acassis@gmail.com>
BREAKING: In an effort to simplify NuttX initialization, NSH_ARCHINIT is
removed. board_app_initialize is also removed. BOARD_LATE_INITIALIZE now
performs all board initialization logic, and is by default enabled. All
references to these symbols are removed. BOARDIOC_INIT remains, but will
result in -ENOTTY when called. It is to be removed in a later commit.
Quick fix: Boards relying on NSH_ARCHINIT should now enable
CONFIG_BOARD_LATE_INITIALIZE instead. If the application needs
fine-grained control over board initialization from userspace, the logic
performed by BOARDIOC_INIT may be copied to the board_finalinitialize
function and used instead via BOARDIOC_FINALINIT. All
board_app_initialize logic provided by NuttX is now moved to
board_late_initialize, and the same should be done for out-of-tree
boards.
Signed-off-by: Matteo Golin <matteo.golin@gmail.com>
debug.h is a NuttX-specific, non-POSIX header. Placing it in the
top-level include/ directory creates naming conflicts with external
projects that define their own debug.h.
This commit moves the canonical header to include/nuttx/debug.h,
following the NuttX convention for non-POSIX/non-standard headers,
and updates all in-tree references.
A backward-compatibility shim is left at include/debug.h that
emits a deprecation #warning and re-includes <nuttx/debug.h>,
allowing out-of-tree code to continue building while migrating.
Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
Refactor heap pointer storage by moving us_heap field from userspace_s
to the nested userspace_data_s structure, enabling future extensibility
of user-space data without modifying the core userspace_s interface across
all board-specific implementations.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
Add validation to ensure allocated stack size does not exceed TLS_MAXSTACK when
CONFIG_TLS_ALIGNED is enabled, and verify proper stack alignment using STACK_ALIGN_MASK
across all architectures. This improves stack safety and prevents potential TLS overflow conditions.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
Rename STACK_ALIGNMENT macro to STACKFRAME_ALIGN throughout the codebase
to provide clearer naming semantics. The new name better reflects the macro's
purpose of frame alignment rather than general stack alignment.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
Move stack alignment and kernel stack macros from architecture-specific internal
headers to public include/nuttx/irq.h. Consolidates duplicate definitions across
17 architecture families, reducing code duplication while enabling common code
to access these core alignment utilities without architecture dependencies.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
Make sure interrupt stack is colored before IRQ is enabled.
Currently, after calling irq_initialize in nx_start to
enable interrupts, there is still a period of execution
path before the interrupt stack is colored.
Signed-off-by: guoshengyuan1 <guoshengyuan1@xiaomi.com>
After irq_dispatch finished, the interrupt stack will be checked to
determine whether overflow occurs.
The relevant configuration reuses the configuration of stack overflow
detection during context switching.
Signed-off-by: guoshengyuan1 <guoshengyuan1@xiaomi.com>
Many times, context switching does not occur when the thread stack
memory is almost exhausted, so we need to mofify up_check_tcbstack to
accurately detect it.
Co-authored-by: Chengdong Wang <wangchengdong@lixiang.com>
Signed-off-by: guoshengyuan1 <guoshengyuan1@xiaomi.com>
Complete the missing scheduling information in some architectures
In these architectures (riscv, avr, tricor) context switching
can occur in both up_switch_context and xx_doirq
Co-authored-by: yinshengkai <yinshengkai@xiaomi.com>
Signed-off-by: guoshengyuan1 <guoshengyuan1@xiaomi.com>
These archs only align the size of the stack, forgeting to do the
stack start addr alignment, this patch fixes it.
Signed-off-by: Chengdong Wang <wangchengdong@lixiang.com>
Renaming "modlib" to "libelf" is more in line with the implementation content,
which makes it easier for individual developers to understand the capabilities of this module.
CONFIG_LIBC_MODLIB -> CONFIG_LIBC_ELF
Signed-off-by: chao an <anchao.archer@bytedance.com>
test:
1.use mps3-an547 build helloxx as module and run it
2.use qemu-armv7a:knsh test kernel build helloxx and run it
Signed-off-by: anjiahao <anjiahao@xiaomi.com>
Inline & inline_function both used make confuze, let's modify all inline
in irq.h to inline_function, also clear the always_inline_funcion
declaration.
Signed-off-by: buxiasen <buxiasen@xiaomi.com>
Most tools used for compliance and SBOM generation use SPDX identifiers
This change brings us a step closer to an easy SBOM generation.
Signed-off-by: Alin Jerpelea <alin.jerpelea@sony.com>
reason:
When entering an exception or interrupt, there are two sets of registers:
one is the "running regs", which we need to save,
and the other is the "ready to running regs", which we may soon use.
For consistency in logic, we can always store the "running regs" in the regs field of g_running_tasks,
otherwise it may lead to errors in the storage location of the "running regs."
When we need to access the "running regs," we should uniformly retrieve them from the regs field of g_running_tasks.
As the next step, we will rename the set_current_regs/up_current_regs functions
for each architecture to more appropriate names, solely for the purpose of identifying interrupts.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
reason:
Replace "inline" with "inline_function" for "up_interrupt_context" to ensure consistency with other arch
Signed-off-by: hujun5 <hujun5@xiaomi.com>
Some app with same code runs on different cores in AMP mode,
need the physical core on which the function is called.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>
for the citimon stats:
thread 0: thread 1:
enter_critical (t0)
up_switch_context
note suspend thread0 (t1)
thread running
IRQ happen, in ISR:
post thread0
up_switch_context
note resume thread0 (t2)
ISR continue f1
ISR continue f2
...
ISR continue fn
leave_critical (t3)
You will see, the thread 0, critical_section time is:
(t1 - t0) + (t3 - t2)
BUT, this result contains f1 f2 .. fn time spent, it is wrong
to tell user thead0 hold the critical lots of time but actually
not belong to it.
Resolve:
change the nxsched_suspend/resume_scheduler to real hanppends
Signed-off-by: ligd <liguiding1@xiaomi.com>
reason:
1 On different architectures, we can utilize more optimized strategies
to implement up_current_regs/up_set_current_regs.
eg. use interrupt registersor percpu registers.
code size
before
text data bss dec hex filename
262848 49985 63893 376726 5bf96 nuttx
after
text data bss dec hex filename
262844 49985 63893 376722 5bf92 nuttx
size change -4
Configuring NuttX and compile:
$ ./tools/configure.sh -l qemu-armv8a:nsh_smp
$ make
Running with qemu
$ qemu-system-aarch64 -cpu cortex-a53 -smp 4 -nographic \
-machine virt,virtualization=on,gic-version=3 \
-net none -chardev stdio,id=con,mux=on -serial chardev:con \
-mon chardev=con,mode=readline -kernel ./nuttx
Signed-off-by: hujun5 <hujun5@xiaomi.com>
