tools/nolibc: Make dup2() rely on dup3() when available

A recent boot failure on 5.4-rc3 on arm64 revealed that sys_dup2()
is not available and that only sys_dup3() is implemented.  This commit
detects this and falls back to sys_dup3() when available.  This is a
port of nolibc's upstream commit fd5272ec2c66 to the Linux kernel.
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com> [arm64]
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/include/nolibc/nolibc.h

@@ -1502,10 +1502,22 @@ int sys_dup(int fd)
 	return my_syscall1(__NR_dup, fd);
 }
 
+#ifdef __NR_dup3
+static __attribute__((unused))
+int sys_dup3(int old, int new, int flags)
+{
+	return my_syscall3(__NR_dup3, old, new, flags);
+}
+#endif
+
 static __attribute__((unused))
 int sys_dup2(int old, int new)
 {
+#ifdef __NR_dup3
+	return my_syscall3(__NR_dup3, old, new, 0);
+#else
 	return my_syscall2(__NR_dup2, old, new);
+#endif
 }
 
 static __attribute__((unused))
@@ -1876,6 +1888,20 @@ int dup2(int old, int new)
 	return ret;
 }
 
+#ifdef __NR_dup3
+static __attribute__((unused))
+int dup3(int old, int new, int flags)
+{
+	int ret = sys_dup3(old, new, flags);
+
+	if (ret < 0) {
+		SET_ERRNO(-ret);
+		ret = -1;
+	}
+	return ret;
+}
+#endif
+
 static __attribute__((unused))
 int execve(const char *filename, char *const argv[], char *const envp[])
 {