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>
This change fixes NuttX’s CMake support when NuttX is embedded
in another project via add_subdirectory(). CMake’s CMAKE_SOURCE_DIR
and CMAKE_BINARY_DIR refer to the outermost project, causing NuttX
to access its .config, generated files, host tools, and build artifacts
in the parent project’s directories. The fix introduces NUTTX_DIR and
NUTTX_BINARY_DIR, based on CMAKE_CURRENT_SOURCE_DIR and
CMAKE_CURRENT_BINARY_DIR, and consistently uses them for NuttX
self-references while preserving existing standalone builds. It fixes
the Kconfig initialization failure reported in #19697 and allows an
embedded sim:nsh build to configure, build, and boot successfully.
The change affects only the CMake build system (not Make or Kconfig
defaults), requires the corresponding nuttx-apps change, and does not
extend add_subdirectory() support to cross-compiled non-sim boards due
to CMake’s toolchain-file limitation.
Fixes#19697.
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Alan Carvalho de Assis <acassis@gmail.com>
The compiler-rt builtins build globs every arm/*.S source, but several of
those hand-written assembly files require FPU features the target may not
have. Upstream compiler-rt selects them conditionally; NuttX did not, so
BUILTIN_COMPILER_RT builds for single-precision-FPU Arm targets (e.g.
Cortex-M33, -mfpu=fpv5-sp-d16) failed to assemble with errors such as
"selected FPU does not support instruction -- vadd.f64".
Filter the source list to match the configured FPU, in both the Makefile
and CMake builds:
- chkstk.S / chkstk2.S are Windows/MinGW-only stack probes, always dropped;
- with no hardware FPU (!CONFIG_ARCH_FPU) all arm/*vfp.S are dropped;
- with a single-precision FPU (!CONFIG_ARCH_DPFPU) the double-precision
*df*vfp.S routines are dropped.
Reproduced against compiler-rt 17.0.1 with arm-none-eabi-gcc 14.2 using the
Cortex-M33 single-precision flags: 18 of 86 arm/*.S files failed to assemble
(17 double-precision *df*vfp.S plus chkstk.S); after the filter all remaining
68 files assemble cleanly.
Fixes: https://github.com/apache/nuttx/issues/17386
Generated-by: Claude (Anthropic)
Signed-off-by: Udit Jain <uditjainstjis@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>
compiler-rt/Make.defs:45: target `bin/compiler-rt/compiler-rt/lib/builtins' given more than once in the same rule.
compiler-rt/Make.defs:45: target `kbin/compiler-rt/compiler-rt/lib/builtins' given more than once in the same rule.
Signed-off-by: bijunda <bijunda@bytedance.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>
1. remove_item It needs to use the full path to exclude the file, otherwise the exclusion will fail
2. No include path was added, resulting in the header file not being found
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
remove not related comments from libs/libbuiltin/CMakeLists.txt and
libs/libxx/CMakeLists.txt. These are a copy paste from a Makefile
which doesn't make sense for these files.
Signed-off-by: raiden00pl <raiden00@railab.me>
All implementations of gcov are sunk to the kernel implementation
1. Support three dump modes: serial port output, single file output, standard output
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
Bringing the code coverage option when linking may cause gcc or g++ to automatically link the libgcov.a that comes with the toolchain.
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
Fix some misspelled field names.
These field names seem to be used only in private contexts.
Thus, the probability of external code accessing these fields is very
low.
In the rare case of external usage, compile time errors will easily
direct users to the new field name.
When enable CONFIG_STACK_CANARIES, in general, the stack check in the __gcov_fork function is:
" return fork();
18: e59f3020 ldr r3, [pc, #32] @ 40 <__gcov_fork+0x40>
1c: e5932000 ldr r2, [r3]
20: e59d3004 ldr r3, [sp, #4]
24: e0332002 eors r2, r3, r2
28: e3a03000 mov r3, #0
2c: 1a000002 bne 3c <__gcov_fork+0x3c>"
r3 is obtained by taking the value of sp offset. But after opening thumb, the second comparison value in
"8c6: 4a06 ldr r2, [pc, #24] @ (8e0 <__gcov_fork+0x30>)
8c8: 6811 ldr r1, [r2, #0]
8ca: 687a ldr r2, [r7, #4]
8cc: 4051 eors r1, r2"
is obtained through r7. Since r7 stores the stack address at this time, which stores the address of the parent process, the stack out of bounds will occur in the child process
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
In devices without storage media, you can export data to the
command line and then generate the corresponding gcda file
It can save the result output by calling __gcov_info_to_gcda
The usage is similar to:
https://gcc.gnu.org/onlinedocs/gcc/Freestanding-Environments.html#Profiling-and-Test-Coverage-in-Freestanding-Environments
Usage:
./tools/configure.sh qemu-armv7a:nsh
Modify the configuration
+CONFIG_COVERAGE_ALL=y
+CONFIG_COVERAGE_MINI=y
+CONFIG_SYSTEM_GCOV=y
Run:
qemu-system-arm -cpu cortex-a7 -nographic -smp 4 \
-machine virt,virtualization=off,gic-version=2 \
-net none -chardev stdio,id=con,mux=on -serial chardev:con \
-mon chardev=con,mode=readline -kernel ./nuttx/nuttx -semihosting -s | tee gcov.txt
./nuttx/tools/gcov_convert.py -i ./gcov.txt
./nuttx/tools/gcov.sh -t arm-none-eabi-gcov
Signed-off-by: yinshengkai <yinshengkai@xiaomi.com>
Currently, there are four code coverage statistics implementations:
1. GCC native implementation
2. CLANG native implementation
3. GCC coverage nuttx mini version
4. CLANG coverage nuttx mini version
Coverage Support:
GCC native implementation CLANG native implementation GCC coverage nuttx mini version CLANG coverage nuttx mini version
Compiler version requirements ALL ALL GCC 13.2 and below CLANG 17.0 and below
Program coverage statistics support Main program √ √ √ √
Program coverage statistics support Interrupt program X √ √ √
Configuration options CONFIG_COVERAGE_TOOLCHAIN CONFIG_COVERAGE_COMPILER_RT CONFIG_COVERAGE_MINI CONFIG_COVERAGE_MINI
Platform Support ARM √ √ √ √
ARM64 √ √
(Coming soon, not yet merged)
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
1. Excerpted from: https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/blob/main/samples/src/cpp-baremetal-semihosting-prof/proflib.c
2. Since llvm profile supports more than just gcov, and some features have not yet been explored, two clang gcov implementations are supported after this patch
3. Using this lib only supports the gcov compilation options of "-fprofile-instr-generate -fcoverage-mapping"
4. This file is heavily dependent on the compiler clang version, and is currently aligned with ci, supporting 17.0.1 and below. 18 and above are not supported by this library due to different internal implementations of the compiler
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
1. bin and kbin folders are dynamically generated
2. Context comes before depend, so the bin and kbin folders are created in the context construction phase. When the depend process comes, each library is downloaded, and a relative bin/xxx and kbin/xxx directory is created for each library to place files. This is to prevent duplicate file names.
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
1. Since the implementation of gcov has changed since clang17, versions before clang17 need to use the libunwind.a file
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
1. enable CONFIG_BUILTIN_COMPILER_RT to built libclang_rt.builtins-xxx.a and no longer use the compiler's built-in
2. Modify clang version acquisition to get two decimal points
3. It has been ported to support four architectures: ARM, ARM64, RISCV, and x86_64, among which ARM has been validated
Signed-off-by: wangmingrong1 <wangmingrong1@xiaomi.com>
Marco Casaroli
Alan Carvalho de Assis
Udit Jain
bijunda
Piyush Patle
Huang Qi
wangmingrong1
raiden00pl
chenxiaoyi
buxiasen
Lars Kruse
yinshengkai