clone3 on ARC (was Re: [PATCH v3 2/2] arch: wire-up clone3() syscall)

[Vineet Gupta]

On 6/4/19 2:29 PM, Christian Brauner wrote:
> On Tue, Jun 04, 2019 at 08:40:01PM +0200, Arnd Bergmann wrote:
>> On Tue, Jun 4, 2019 at 6:09 PM Christian Brauner <christian@xxxxxxxxxx> wrote:
>>>
>>> Wire up the clone3() call on all arches that don't require hand-rolled
>>> assembly.
>>>
>>> Some of the arches look like they need special assembly massaging and it is
>>> probably smarter if the appropriate arch maintainers would do the actual
>>> wiring. Arches that are wired-up are:
>>> - x86{_32,64}
>>> - arm{64}
>>> - xtensa
>>
>> The ones you did look good to me. I would hope that we can do all other
>> architectures the same way, even if they have special assembly wrappers
>> for the old clone(). The most interesting cases appear to be ia64, alpha,
>> m68k and sparc, so it would be good if their maintainers could take a
>> look.
> 
> Yes, agreed. They can sort this out even after this lands.
> 
>>
>> What do you use for testing? Would it be possible to override the
>> internal clone() function in glibc with an LD_PRELOAD library
>> to quickly test one of the other architectures for regressions?
> 
> I have a test program that is rather horrendously ugly and I compiled
> kernels for x86 and the arms and tested in qemu. The program basically
> looks like [1].

I just got around to fixing this for ARC (patch to follow after we sort out the
testing) and was trying to use the test case below for a qucik and dirty smoke
test (so existing toolchain lacking with headers lacking NR_clone3 or struct
clone_args etc). I did hack those up, but then spotted below

uapi/linux/sched.h

|    struct clone_args {
|	__aligned_u64 flags;
|	__aligned_u64 pidfd;
|	__aligned_u64 child_tid;
|	__aligned_u64 parent_tid;
..
..

Are all clone3 arg fields supposed to be 64-bit wide, even things like @child_tid,
@tls .... which are traditionally ARCH word wide ?


> 
> Christian
> 
> [1]:
> #define _GNU_SOURCE
> #include <err.h>
> #include <errno.h>
> #include <fcntl.h>
> #include <linux/sched.h>
> #include <linux/types.h>
> #include <sched.h>
> #include <signal.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/mount.h>
> #include <sys/socket.h>
> #include <sys/stat.h>
> #include <sys/syscall.h>
> #include <sys/sysmacros.h>
> #include <sys/types.h>
> #include <sys/un.h>
> #include <sys/wait.h>
> #include <unistd.h>
> 
> static pid_t raw_clone(struct clone_args *args)
> {
> 	return syscall(__NR_clone3, args, sizeof(struct clone_args));
> }
> 
> static pid_t raw_clone_legacy(int *pidfd, unsigned int flags)
> {
> 	return syscall(__NR_clone, flags, 0, pidfd, 0, 0);
> }
> 
> static int wait_for_pid(pid_t pid)
> {
> 	int status, ret;
> 
> again:
> 	ret = waitpid(pid, &status, 0);
> 	if (ret == -1) {
> 		if (errno == EINTR)
> 			goto again;
> 
> 		return -1;
> 	}
> 
> 	if (ret != pid)
> 		goto again;
> 
> 	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
> 		return -1;
> 
> 	return 0;
> }
> 
> #define ptr_to_u64(ptr) ((__u64)((uintptr_t)(ptr)))
> #define u64_to_ptr(n) ((uintptr_t)((__u64)(n)))
> 
> int main(int argc, char *argv[])
> {
> 	int pidfd = -1;
> 	pid_t parent_tid = -1, pid = -1;
> 	struct clone_args args = {0};
> 	args.parent_tid = ptr_to_u64(&parent_tid);
> 	args.pidfd = ptr_to_u64(&pidfd);
> 	args.flags = CLONE_PIDFD | CLONE_PARENT_SETTID;
> 	args.exit_signal = SIGCHLD;
> 
> 	pid = raw_clone(&args);
> 	if (pid < 0) {
> 		fprintf(stderr, "%s - Failed to create new process\n",
> 			strerror(errno));
> 		exit(EXIT_FAILURE);
> 	}
> 
> 	if (pid == 0) {
> 		printf("I am the child with pid %d\n", getpid());
> 		exit(EXIT_SUCCESS);
> 	}
> 
> 	printf("raw_clone: I am the parent. My child's pid is   %d\n", pid);
> 	printf("raw_clone: I am the parent. My child's pidfd is %d\n",
> 	       *(int *)args.pidfd);
> 	printf("raw_clone: I am the parent. My child's paren_tid value is %d\n",
> 	       *(pid_t *)args.parent_tid);
> 
> 	if (wait_for_pid(pid))
> 		exit(EXIT_FAILURE);
> 
> 	if (pid != *(pid_t *)args.parent_tid)
> 		exit(EXIT_FAILURE);
> 
> 	close(pidfd);
> 
> 	printf("\n\n");
> 	pidfd = -1;
> 	pid = raw_clone_legacy(&pidfd, CLONE_PIDFD | SIGCHLD);
> 	if (pid < 0) {
> 		fprintf(stderr, "%s - Failed to create new process\n",
> 			strerror(errno));
> 		exit(EXIT_FAILURE);
> 	}
> 
> 	if (pid == 0) {
> 		printf("I am the child with pid %d\n", getpid());
> 		exit(EXIT_SUCCESS);
> 	}
> 
> 	printf("raw_clone_legacy: I am the parent. My child's pid is   %d\n",
> 	       pid);
> 	printf("raw_clone_legacy: I am the parent. My child's pidfd is %d\n",
> 	       pidfd);
> 
> 	if (wait_for_pid(pid))
> 		exit(EXIT_FAILURE);
> 
> 	if (pid != *(pid_t *)args.parent_tid)
> 		exit(EXIT_FAILURE);
> 
> 	return 0;
> }
>