[Bug libc/31468] New: sigisemptyset returns true when the set contains signals larger than 34

["shankerwangmiao at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31468

            Bug ID: 31468
           Summary: sigisemptyset returns true when the set contains
                    signals larger than 34
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: shankerwangmiao at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Hi,

I found that there might be a bug in `sigisemptyset`. The following code
reproduces this issue:

```c
#define _GNU_SOURCE
#include<signal.h>
#include<stdio.h>
#include<stdlib.h>

int main(){
        sigset_t set;
        int rc = sigemptyset(&set);
        if (rc < 0){
                perror("sigemptyset");
                exit(1);
        }
        printf("NSIG=%d\n", NSIG);
        rc = sigaddset(&set, 34);
        if (rc < 0){
                perror("sigaddset");
                exit(1);
        }
        printf("isemptyset: %d\n", sigisemptyset(&set));
        printf("ismember(34): %d\n", sigismember(&set, 34));

        return 0;
}
```

`sigisemptyset` returns 1 even when the signal number 34 is in the set. 

The bug may be related to the following code:

https://elixir.bootlin.com/glibc/glibc-2.39/source/sysdeps/unix/sysv/linux/sigsetops.h#L69

where the variable `ret` is declared as `int` rather than `unsigned long int`,
which is used in `struct __sigset_t`. On 64bit platforms where `long` is 64
bits and `int` is 32 bits, the above code leaves the higher 32 bits of each
`__val` member unchecked.

I wonder if this is intended or a bug.

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