[PATCH v2 nolibc 17/53] tools/nolibc/unistd: add syscall()

[Paul E. McKenney]

From: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>

syscall() is used by "normal" libcs to allow users to directly call
syscalls.
By having the same syntax inside nolibc users can more easily write code
that works with different libcs.

The macro logic is adapted from systemtaps STAP_PROBEV() macro that is
released in the public domain / CC0.

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 tools/include/nolibc/unistd.h                | 15 +++++++++++++++
 tools/testing/selftests/nolibc/nolibc-test.c |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/tools/include/nolibc/unistd.h b/tools/include/nolibc/unistd.h
index ac7d53d986cd..0e832e10a0b2 100644
--- a/tools/include/nolibc/unistd.h
+++ b/tools/include/nolibc/unistd.h
@@ -56,6 +56,21 @@ int tcsetpgrp(int fd, pid_t pid)
 	return ioctl(fd, TIOCSPGRP, &pid);
 }
 
+#define _syscall(N, ...)                                                      \
+({                                                                            \
+	long _ret = my_syscall##N(__VA_ARGS__);                               \
+	if (_ret < 0) {                                                       \
+		SET_ERRNO(-_ret);                                             \
+		_ret = -1;                                                    \
+	}                                                                     \
+	_ret;                                                                 \
+})
+
+#define _syscall_narg(...) __syscall_narg(__VA_ARGS__, 6, 5, 4, 3, 2, 1, 0)
+#define __syscall_narg(_0, _1, _2, _3, _4, _5, _6, N, ...) N
+#define _syscall_n(N, ...) _syscall(N, __VA_ARGS__)
+#define syscall(...) _syscall_n(_syscall_narg(__VA_ARGS__), ##__VA_ARGS__)
+
 /* make sure to include all global symbols */
 #include "nolibc.h"
 
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index f042a6436b6b..54bf91847af3 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -588,6 +588,8 @@ int run_syscall(int min, int max)
 		CASE_TEST(waitpid_child);     EXPECT_SYSER(1, waitpid(getpid(), &tmp, WNOHANG), -1, ECHILD); break;
 		CASE_TEST(write_badf);        EXPECT_SYSER(1, write(-1, &tmp, 1), -1, EBADF); break;
 		CASE_TEST(write_zero);        EXPECT_SYSZR(1, write(1, &tmp, 0)); break;
+		CASE_TEST(syscall_noargs);    EXPECT_SYSEQ(1, syscall(__NR_getpid), getpid()); break;
+		CASE_TEST(syscall_args);      EXPECT_SYSER(1, syscall(__NR_fstat, 0, NULL), -1, EFAULT); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */
-- 
2.40.1