question about prctl return value type

Florian Weimer
Wed Jul 24 10:48:00 GMT 2019

* Yang Xu:

> Since kernel syscall use long value for return, why we set int in
> sys/prctl.h(glibc). as below:
> /include/sys/prctl.h
>    1 #ifndef _SYS_PRCTL_H
>    2 #include_next <sys/prctl.h>
>    3 
>    4 # ifndef _ISOMAC
>    5 
>    6 extern int __prctl (int __option, ...);
>    7 
>    8 # endif /* !_ISOMAC */
>    9 #endif

Note that the actual user-visible header is
sysdeps/unix/sysv/linux/sys/prctl.h, but it has the same issue.

> If we calling prctl(PR_SET_TIMERSLACK, ULONG_MAX) and then calling prctl(PR_GET_TIMERSLACK), the value
> will be truncated into INT_MAX(or convered into unsinged,it is UINT_MAX) on 64bit machine. Or, this is a 
> glibc limitation for prctl interfaces?

I think this is a glibc limitation/bug.  The return type should probably
be __register_t (a type that is currently woefully underused).  We
cannot simply change the return time because once applications are built
against the new prototype, we need to ensure that they also use the new

Would you please file a bug for this?
<> is our bug tracker.


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