[PATCH 0/2] tools/nolibc: fork: fix on s390 and add test

[PATCH 0/2] tools/nolibc: fork: fix on s390 and add test

[Thomas Weißschuh]

The generic fork() implementation in nolibc falls back to the clone()
syscall. On s390 the first two arguments to clone() are swapped compared
to other architectures, breaking the implementation in nolibc.

Add a custom implementation of fork() to s390 that works.

While at it also add a testcase for fork().

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Thomas Weißschuh (2):
      tools/nolibc: s390: provide custom implementation for sys_fork
      tools/nolibc: add testcase for fork()/waitpid()

 tools/include/nolibc/arch-s390.h             |  8 ++++++++
 tools/include/nolibc/sys.h                   |  2 ++
 tools/testing/selftests/nolibc/nolibc-test.c | 20 ++++++++++++++++++++
 3 files changed, 30 insertions(+)
---
base-commit: c1c4f33b6be9b3412d9e0ba01b367f4ffe47c379
change-id: 20230415-nolibc-fork-b7087a345166

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

[PATCH 1/2] tools/nolibc: s390: provide custom implementation for sys_fork

[Thomas Weißschuh]

On s390 the first two arguments to the clone() syscall are swapped,
as documented in clone(2).

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/arch-s390.h | 8 ++++++++
 tools/include/nolibc/sys.h       | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/tools/include/nolibc/arch-s390.h b/tools/include/nolibc/arch-s390.h
index 6b0e54ed543d..db4ea51a4dbb 100644
--- a/tools/include/nolibc/arch-s390.h
+++ b/tools/include/nolibc/arch-s390.h
@@ -5,6 +5,7 @@
 
 #ifndef _NOLIBC_ARCH_S390_H
 #define _NOLIBC_ARCH_S390_H
+#include <asm/signal.h>
 #include <asm/unistd.h>
 
 /* The struct returned by the stat() syscall, equivalent to stat64(). The
@@ -223,4 +224,11 @@ void *sys_mmap(void *addr, size_t length, int prot, int flags, int fd,
 	return (void *)my_syscall1(__NR_mmap, &args);
 }
 #define sys_mmap sys_mmap
+
+static __attribute__((unused))
+pid_t sys_fork(void)
+{
+	return my_syscall5(__NR_clone, 0, SIGCHLD, 0, 0, 0);
+}
+#define sys_fork sys_fork
 #endif // _NOLIBC_ARCH_S390_H
diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index bea9760dbd16..f5a450153a63 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -336,6 +336,7 @@ void exit(int status)
  * pid_t fork(void);
  */
 
+#ifndef sys_fork
 static __attribute__((unused))
 pid_t sys_fork(void)
 {
@@ -351,6 +352,7 @@ pid_t sys_fork(void)
 #error Neither __NR_clone nor __NR_fork defined, cannot implement sys_fork()
 #endif
 }
+#endif
 
 static __attribute__((unused))
 pid_t fork(void)

-- 
2.40.0

Re: [PATCH 1/2] tools/nolibc: s390: provide custom implementation for sys_fork

[Sven Schnelle]

Thomas Weißschuh <linux@weissschuh.net> writes:

> On s390 the first two arguments to the clone() syscall are swapped,
> as documented in clone(2).
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  tools/include/nolibc/arch-s390.h | 8 ++++++++
>  tools/include/nolibc/sys.h       | 2 ++
>  2 files changed, 10 insertions(+)

Acked-by: Sven Schnelle <svens@linux.ibm.com>

[PATCH 2/2] tools/nolibc: add testcase for fork()/waitpid()

[Thomas Weißschuh]

On s390 the arguments to clone() which is used by fork() are different
than other archs.
Make sure everything works correctly.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/testing/selftests/nolibc/nolibc-test.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 888da60eb5ba..d294338cf141 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -474,6 +474,25 @@ static int test_getpagesize(void)
 	return !c;
 }
 
+static int test_fork(void)
+{
+	int status;
+	pid_t pid = fork();
+
+	switch (pid) {
+	case -1:
+		return 1;
+
+	case 0:
+		exit(123);
+
+	default:
+		pid = waitpid(pid, &status, 0);
+
+		return pid == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 123;
+	}
+}
+
 /* Run syscall tests between IDs <min> and <max>.
  * Return 0 on success, non-zero on failure.
  */
@@ -530,6 +549,7 @@ int run_syscall(int min, int max)
 		CASE_TEST(dup3_0);            tmp = dup3(0, 100, 0);  EXPECT_SYSNE(1, tmp, -1); close(tmp); break;
 		CASE_TEST(dup3_m1);           tmp = dup3(-1, 100, 0); EXPECT_SYSER(1, tmp, -1, EBADF); if (tmp != -1) close(tmp); break;
 		CASE_TEST(execve_root);       EXPECT_SYSER(1, execve("/", (char*[]){ [0] = "/", [1] = NULL }, NULL), -1, EACCES); break;
+		CASE_TEST(fork);              EXPECT_SYSZR(1, test_fork()); break;
 		CASE_TEST(getdents64_root);   EXPECT_SYSNE(1, test_getdents64("/"), -1); break;
 		CASE_TEST(getdents64_null);   EXPECT_SYSER(1, test_getdents64("/dev/null"), -1, ENOTDIR); break;
 		CASE_TEST(gettimeofday_null); EXPECT_SYSZR(1, gettimeofday(NULL, NULL)); break;

-- 
2.40.0

Re: [PATCH 0/2] tools/nolibc: fork: fix on s390 and add test

[Willy Tarreau]

Hi Thomas,

On Sat, Apr 15, 2023 at 11:28:46PM +0200, Thomas Weißschuh wrote:
> The generic fork() implementation in nolibc falls back to the clone()
> syscall. On s390 the first two arguments to clone() are swapped compared
> to other architectures, breaking the implementation in nolibc.
> 
> Add a custom implementation of fork() to s390 that works.
> 
> While at it also add a testcase for fork().
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Thanks for these. Please always Cc the authors of code you're fixing
(e.g. there could be more subtle details that only the author knows
about). Here I think it's OK, but I've CCed Sven and will add him to
your fix.

Thank you!
Willy