linux-kernel - [PATCH 1/2] tools/nolibc: Provide vfork()

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Message-Id: <20250609-arm64-gcs-vfork-exit-v1-1-baad0f085747@kernel.org>
Date: Mon, 09 Jun 2025 16:08:56 +0100
From: Mark Brown <broonie@...nel.org>
To: Willy Tarreau <w@....eu>, 
 Thomas Weißschuh <linux@...ssschuh.net>, 
 Christian Brauner <brauner@...nel.org>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Shuah Khan <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-kselftest@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: [PATCH 1/2] 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.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
 tools/include/nolibc/sys.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 9556c69a6ae1..e056da010f64 100644
--- 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)
+{
+#ifdef __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);

-- 
2.39.5