Re: [PATCH] clone.2: note EINVAL when exit_signal + bad flags

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi Jack,

On 12/2/22 23:44, Jack Pearson wrote:
> Document that Linux will report EINVAL when exit_signal is specified and
> either CLONE_THREAD or CLONE_PARENT is specified.
> 
>  From clone3_args_valid in Linux:
> ```
> 	if ((kargs->flags & (CLONE_THREAD | CLONE_PARENT)) &&
> 	    kargs->exit_signal)
> 		return false;
> ```
> 
> I have verified that this happens on my kernel with a small program, and
> that this doesn't happen with normal `clone` through the glibc helper.

Could you please also send a test program with the glibc wrapper?

BTW, glibc has a clone3(2) wrapper since last year.  It would be interesting to 
document it instead of the raw syscall.

Cheers,

Alex

> 
> The program:
> 
> ```
> #include <stdio.h>
> #include <linux/sched.h>
> #include <signal.h>
> #include <sys/syscall.h>
> #include <unistd.h>
> 
> int main() {
> 	struct clone_args ca = {
> 		.flags = CLONE_THREAD | CLONE_SIGHAND | CLONE_VM,
> 		.exit_signal = SIGCHLD, // comment me out to fix error
> 		.set_tid_size = 0,
> 	};
> 	syscall(SYS_clone3, &ca, sizeof(struct clone_args));
> 	perror("");
> }
> ```
> 
> Signed-off-by: Jack Pearson <jack@pearson.onl>
> ---
>   man2/clone.2 | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/man2/clone.2 b/man2/clone.2
> index 093630859..a0fa50d83 100644
> --- a/man2/clone.2
> +++ b/man2/clone.2
> @@ -1433,6 +1433,16 @@ One of the PIDs specified in
>   .I set_tid
>   was an invalid.
>   .TP
> +.BR EINVAL " (" clone3 "() only)"
> +.\" commit 7f192e3cd316ba58c88dfa26796cf77789dd9872
> +.B CLONE_THREAD
> +or
> +.B CLONE_PARENT
> +was specified in the
> +.I flags
> +mask, but a signal was specified in
> +.I exit_signal.
> +.TP
>   .BR EINVAL " (AArch64 only, Linux 4.6 and earlier)"
>   .I stack
>   was not aligned to a 128-bit boundary.
> --
> 2.35.1
> 

-- 
<http://www.alejandro-colomar.es/>

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