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diff --git a/lib/libc/gen/posix_spawn.c b/lib/libc/gen/posix_spawn.c
--- a/lib/libc/gen/posix_spawn.c
+++ b/lib/libc/gen/posix_spawn.c
@@ -236,7 +236,6 @@
#define PSPAWN_STACK_ALIGN(sz) \
(((sz) + PSPAWN_STACK_ALIGNBYTES) & ~PSPAWN_STACK_ALIGNBYTES)
-#if defined(__i386__) || defined(__amd64__)
/*
* Below we'll assume that _RFORK_THREAD_STACK_SIZE is appropriately aligned for
* the posix_spawn() case where we do not end up calling execvpe and won't ever
@@ -245,7 +244,6 @@
#define _RFORK_THREAD_STACK_SIZE 4096
_Static_assert((_RFORK_THREAD_STACK_SIZE % PSPAWN_STACK_ALIGNMENT) == 0,
"Inappropriate stack size alignment");
-#endif
static int
_posix_spawn_thr(void *data)
@@ -287,10 +285,10 @@
pid_t p;
int pfd;
bool do_pfd;
-#ifdef _RFORK_THREAD_STACK_SIZE
char *stack;
- size_t cnt, stacksz;
+ size_t cnt __used, stacksz;
+#if defined(__i386__) || defined(__amd64__)
stacksz = _RFORK_THREAD_STACK_SIZE;
if (use_env_path) {
/*
@@ -319,6 +317,9 @@
return (ENOMEM);
stacksz = (((uintptr_t)stack + stacksz) & ~PSPAWN_STACK_ALIGNBYTES) -
(uintptr_t)stack;
+#else
+ stack = NULL;
+ stacksz = 0;
#endif
psa.path = path;
psa.fa = fa;
@@ -341,13 +342,16 @@
* a special property of the libthr rtld locks ensure that
* rtld is operational in the child. In particular, libthr
* rtld locks do not store owner' tid into the lock word.
- */
-#ifdef _RFORK_THREAD_STACK_SIZE
- /*
- * x86 stores the return address on the stack, so rfork(2) cannot work
- * as-is because the child would clobber the return address of the
- * parent. Because of this, we must use rfork_thread instead while
- * almost every other arch stores the return address in a register.
+ *
+ * x86 stores the return address on the stack, so rfork(2)
+ * cannot work as-is because the child would clobber the
+ * return address of the parent. Because of this, we must use
+ * rfork_thread instead.
+ *
+ * Every other architecture stores the return address in a
+ * register, the trivial rfork_thread() wrapper is provided
+ * for them. The only minor drawback is that the stack is
+ * temporarily allocated.
*/
if (do_pfd) {
p = pdrfork_thread(&pfd, PD_CLOEXEC | (*sa)->sa_pdflags,
@@ -357,16 +361,7 @@
&psa);
}
free(stack);
-#else
- if (do_pfd) {
- p = pdrfork(&pfd, PD_CLOEXEC | (*sa)->sa_pdflags, RFSPAWN);
- } else {
- p = rfork(RFSPAWN);
- }
- if (p == 0)
- /* _posix_spawn_thr does not return */
- _posix_spawn_thr(&psa);
-#endif
+
/*
* The above block should leave us in a state where we've either
* succeeded and we're ready to process the results, or we need to
diff --git a/lib/libsys/Symbol.sys.map b/lib/libsys/Symbol.sys.map
--- a/lib/libsys/Symbol.sys.map
+++ b/lib/libsys/Symbol.sys.map
@@ -182,6 +182,7 @@
rename;
revoke;
rfork;
+ rfork_thread;
rmdir;
rtprio;
rtprio_thread;
@@ -391,6 +392,7 @@
FBSD_1.9 {
pdrfork;
+ pdrfork_thread;
};
FBSDprivate_1.0 {
diff --git a/lib/libsys/aarch64/Makefile.sys b/lib/libsys/aarch64/Makefile.sys
--- a/lib/libsys/aarch64/Makefile.sys
+++ b/lib/libsys/aarch64/Makefile.sys
@@ -1,6 +1,8 @@
MIASM:= ${MIASM:Nfreebsd[467]_*}
SRCS+= __vdso_gettc.c \
+ pdrfork_thread_gen.c \
+ rfork_thread_gen.c \
sched_getcpu_gen.c
MDASM= cerror.S \
diff --git a/lib/libsys/amd64/Symbol.sys.map b/lib/libsys/amd64/Symbol.sys.map
--- a/lib/libsys/amd64/Symbol.sys.map
+++ b/lib/libsys/amd64/Symbol.sys.map
@@ -1,5 +1,4 @@
FBSD_1.0 {
- rfork_thread;
amd64_get_fsbase;
amd64_get_gsbase;
amd64_set_fsbase;
@@ -17,10 +16,6 @@
amd64_set_tlsbase;
};
-FBSD_1.9 {
- pdrfork_thread;
-};
-
FBSDprivate_1.0 {
_vfork;
};
diff --git a/lib/libsys/arm/Makefile.sys b/lib/libsys/arm/Makefile.sys
--- a/lib/libsys/arm/Makefile.sys
+++ b/lib/libsys/arm/Makefile.sys
@@ -1,4 +1,6 @@
SRCS+= __vdso_gettc.c \
+ pdrfork_thread_gen.c \
+ rfork_thread_gen.c \
sched_getcpu_gen.c
MDASM= \
diff --git a/lib/libsys/i386/Symbol.sys.map b/lib/libsys/i386/Symbol.sys.map
--- a/lib/libsys/i386/Symbol.sys.map
+++ b/lib/libsys/i386/Symbol.sys.map
@@ -10,7 +10,6 @@
i386_set_ldt;
i386_set_watch;
i386_vm86;
- rfork_thread;
};
FBSD_1.6 {
@@ -20,10 +19,6 @@
x86_pkru_unprotect_range;
};
-FBSD_1.9 {
- pdrfork_thread;
-};
-
FBSDprivate_1.0 {
_vfork;
};
diff --git a/lib/libsys/pdrfork_thread_gen.c b/lib/libsys/pdrfork_thread_gen.c
new file mode 100644
--- /dev/null
+++ b/lib/libsys/pdrfork_thread_gen.c
@@ -0,0 +1,34 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2026 The FreeBSD Foundation
+ *
+ * This software were developed by
+ * Konstantin Belousov <kib@FreeBSD.org> under sponsorship from
+ * the FreeBSD Foundation.
+ */
+
+#include <sys/types.h>
+#include <sys/procdesc.h>
+#include <errno.h>
+#include <unistd.h>
+
+pid_t
+pdrfork_thread(int *fdp, int pdflags, int rfflags, void *stack_addr,
+ int (*start_fn)(void *), void *arg)
+{
+ pid_t res;
+ int ret;
+
+ /* See comment in rfork_thread_gen.c. */
+ if (stack_addr != NULL) {
+ errno = EOPNOTSUPP;
+ return (-1);
+ }
+ res = pdrfork(fdp, pdflags, rfflags);
+ if (res == 0) {
+ ret = start_fn(arg);
+ _exit(ret);
+ }
+ return (res);
+}
diff --git a/lib/libsys/powerpc/Makefile.sys b/lib/libsys/powerpc/Makefile.sys
--- a/lib/libsys/powerpc/Makefile.sys
+++ b/lib/libsys/powerpc/Makefile.sys
@@ -1,4 +1,6 @@
SRCS+= __vdso_gettc.c \
+ pdrfork_thread_gen.c \
+ rfork_thread_gen.c \
sched_getcpu_gen.c
MDASM+= cerror.S
diff --git a/lib/libsys/powerpc64/Makefile.sys b/lib/libsys/powerpc64/Makefile.sys
--- a/lib/libsys/powerpc64/Makefile.sys
+++ b/lib/libsys/powerpc64/Makefile.sys
@@ -1,4 +1,6 @@
SRCS+= __vdso_gettc.c \
+ pdrfork_thread_gen.c \
+ rfork_thread_gen.c \
sched_getcpu_gen.c
MDASM+= cerror.S
diff --git a/lib/libsys/rfork_thread_gen.c b/lib/libsys/rfork_thread_gen.c
new file mode 100644
--- /dev/null
+++ b/lib/libsys/rfork_thread_gen.c
@@ -0,0 +1,40 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2026 The FreeBSD Foundation
+ *
+ * This software were developed by
+ * Konstantin Belousov <kib@FreeBSD.org> under sponsorship from
+ * the FreeBSD Foundation.
+ */
+
+#include <errno.h>
+#include <unistd.h>
+
+pid_t
+rfork_thread(int flags, void *stack_addr, int (*start_fn)(void *), void *arg)
+{
+ pid_t res;
+ int ret;
+
+ /*
+ * Generic implementation cannot switch stacks. Only
+ * architecture-specific code knows how to do it. Require
+ * that caller knows that, and refuse to do operate if the
+ * stack was supplied.
+ *
+ * Note that implementations that do switch stack, would fault
+ * immediately if the passed stack is NULL. They do not need
+ * specifically check for the NULL stack value.
+ */
+ if (stack_addr != NULL) {
+ errno = EOPNOTSUPP;
+ return (-1);
+ }
+ res = rfork(flags);
+ if (res == 0) {
+ ret = start_fn(arg);
+ _exit(ret);
+ }
+ return (res);
+}
diff --git a/lib/libsys/riscv/Makefile.sys b/lib/libsys/riscv/Makefile.sys
--- a/lib/libsys/riscv/Makefile.sys
+++ b/lib/libsys/riscv/Makefile.sys
@@ -1,4 +1,6 @@
SRCS+= __vdso_gettc.c \
+ pdrfork_thread_gen.c \
+ rfork_thread_gen.c \
sched_getcpu_gen.c
MDASM= cerror.S \

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