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,
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)
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;
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
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
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Sven Schnelle -
Thomas Weißschuh -
Willy Tarreau