tools/nolibc: Provide vfork()

To allow testing of vfork() support in the arm64 basic-gcs test provide an
implementation for nolibc, using the vfork() syscall if one is available
and otherwise clone3(). We implement in terms of clone3() since the order
of the arguments for clone() varies between architectures.

As for fork() SPARC returns the parent PID rather than 0 in the child
for vfork() so needs custom handling.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250703-arm64-gcs-vfork-exit-v3-2-1e9a9d2ddbbe@kernel.org
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

diff --git a/tools/include/nolibc/arch-sparc.h b/tools/include/nolibc/arch-sparc.h
index 1435172f3dfe33566cd8c61d726455702c804f6a..ca420d843e254b831ed74b968f1b53faeab1b13c 100644 (file)
--- a/tools/include/nolibc/arch-sparc.h
+++ b/tools/include/nolibc/arch-sparc.h
@@ -188,4 +188,20 @@ pid_t sys_fork(void)
 }
 #define sys_fork sys_fork
 
+static __attribute__((unused))
+pid_t sys_vfork(void)
+{
+       pid_t parent, ret;
+
+       parent = getpid();
+       ret = my_syscall0(__NR_vfork);
+
+       /* The syscall returns the parent pid in the child instead of 0 */
+       if (ret == parent)
+               return 0;
+       else
+               return ret;
+}
+#define sys_vfork sys_vfork
+
 #endif /* _NOLIBC_ARCH_SPARC_H */

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index aabac97a7fb0fa635b3d1fa08399dcf215f7b103..295e71d34abadb7f9c7ca995012b4395b6830975 100644 (file)
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -22,6 +22,7 @@
 #include <linux/time.h>
 #include <linux/auxvec.h>
 #include <linux/fcntl.h> /* for O_* and AT_* */
+#include <linux/sched.h> /* for clone_args */
 #include <linux/stat.h>  /* for statx() */
 
 #include "errno.h"
@@ -340,6 +341,34 @@ pid_t fork(void)
        return __sysret(sys_fork());
 }
 
+#ifndef sys_vfork
+static __attribute__((unused))
+pid_t sys_vfork(void)
+{
+#if defined(__NR_vfork)
+       return my_syscall0(__NR_vfork);
+#elif defined(__NR_clone3)
+       /*
+        * clone() could be used but has different argument orders per
+        * architecture.
+        */
+       struct clone_args args = {
+               .flags          = CLONE_VM | CLONE_VFORK,
+               .exit_signal    = SIGCHLD,
+       };
+
+       return my_syscall2(__NR_clone3, &args, sizeof(args));
+#else
+       return __nolibc_enosys(__func__);
+#endif
+}
+#endif
+
+static __attribute__((unused))
+pid_t vfork(void)
+{
+       return __sysret(sys_vfork());
+}
 
 /*
  * int fsync(int fd);