pthread_getaffinity_np issue

[Konstantin Belousov]

On Thu, Sep 24, 2015 at 12:11:21PM -0700, Jason Schulz wrote:
> Hey Konstantin,
> 
> Thanks for the quick response.  The version I'm developing with is the latest release.
> 
> [jason at fb ~/development/git/uxcn/yafd]$ uname -a
> FreeBSD fb 10.2-RELEASE FreeBSD 10.2-RELEASE #0 r286666: Wed Aug 12 15:26:37 UTC 2015     root at releng1.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC  amd64
> 
> I was able to narrow it down to the following,
> 
> #include <stdio.h>
> 
> #include <pthread.h>
> #include <pthread_np.h>
> 
> int main(int argc, char* argv[argc]) {
> 
>   long cs = 0;
> 
>   pthread_t this = pthread_self();
> 
>   cpuset_t cpus;
> 
>   CPU_ZERO(&cpus);
> 
>   int err = pthread_getaffinity_np(this, sizeof(cpus), &cpus);
> 
>   if (err)
>     return err;
> 
>   cs = (long) CPU_COUNT(&cpus);
> 
>   printf("num cpus... %li\n", cs);
> 
>   return 0;
> }
> 
> Compiling with '-D_XOPEN_SOURCE=700',
> 
> [jason at fb /tmp]$ clang -D_XOPEN_SOURCE=700 -pthread -o num_cpus num_cpus.c
> num_cpus.c:21:15: warning: implicit declaration of function '__bitcountl' is invalid in C99 [-Wimplicit-function-declaration]
>   cs = (long) CPU_COUNT(&cpus);
>               ^
> /usr/include/sys/cpuset.h:63:24: note: expanded from macro 'CPU_COUNT'
> #define CPU_COUNT(p)                    BIT_COUNT(CPU_SETSIZE, p)
>                                         ^
> /usr/include/sys/bitset.h:185:14: note: expanded from macro 'BIT_COUNT'
>                 __count += __bitcountl((p)->__bits[__i]);               \
>                            ^
> 1 warning generated.
> /tmp/num_cpus-560a33.o: In function `main':
> num_cpus.c:(.text+0xbd): undefined reference to `__bitcountl'
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
> 
> However compiling without '-D_XOPEN_SOURCE=700' works,
> 
> [jason at fb /tmp]$ clang -pthread -o num_cpus num_cpus.c
> [jason at fb /tmp]$
> 
> Should I file a bug report?

So your issue only appears when you specify _XOPEN_SOURCE.  This is reasonable,
because __bitcount stuff in sys/types.h was put under _BSD_VISIBLE protection.
I am not sure why and I Cc:ed the author of the change.

IMO all symbols from __bitcount* are in the private namespace and could
be made unconditionally accessible, to avoid surprises.  I put the patch
at the end of the message which does this.

That said, pthread_np.h is not specified by POSIX/X/Open, so your use of
the header and affinity functionality is not covered by _XOPEN_SOURCE
contract.  The consequences of mixing implementation-specific headers
and request for the standard-compliance can be arbitrary.

> 
> -J
> 
> On Thu, Sep 24, 2015 at 09:32:46PM +0300, Konstantin Belousov wrote:
> > On Thu, Sep 24, 2015 at 11:11:27AM -0700, Jason Schulz wrote:
> > > I'm having an issue using the non-posix thread affinity methods.  Specifically, I'm having trouble using CPU_COUNT.  I'm trying to use the following code to get the current number of processors in a processes affinity...
> > > 
> > > 
> > > 
> > > long cs = 0;
> > > 
> > > #if defined(HAVE_LINUX) || defined(HAVE_FREEBSD)
> > > 
> > > pthread_t this = pthread_self();
> > > 
> > > cpu_set_t cpus;
> > > 
> > > CPU_ZERO(&cpus);
> > > 
> > > int err = pthread_getaffinity_np(this, sizeof(cpus), &cpus);
> > > 
> > > if (err)
> > >   return err;
> > > 
> > > cs = (long) CPU_COUNT(&cpus);
> > > 
> > > 
> > > 
> > > However, I get the compiler error...
> > > 
> > > 
> > > 
> > > clang -DHAVE_CONFIG_H -I.      -g -O2 -D_THREAD_SAFE -pthread -pipe -std=c99 -D_XOPEN_SOURCE=700 -pedantic -Wall -Wextra -Wsign-conversion -Wconversion -Werror -MT thread.o -MD -MP -MF .deps/thread.Tpo -c -o thread.o thread.c
> > > thread.c:85:15: error: implicit declaration of function '__bitcountl' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
> > >   cs = (long) CPU_COUNT(&cpus);
> > >               ^
> > > /usr/include/sys/cpuset.h:63:24: note: expanded from macro 'CPU_COUNT'
> > > #define CPU_COUNT(p)                    BIT_COUNT(CPU_SETSIZE, p)
> > >                                         ^
> > > /usr/include/sys/bitset.h:185:14: note: expanded from macro 'BIT_COUNT'
> > >                 __count += __bitcountl((p)->__bits[__i]);               \
> > >                            ^
> > > 1 error generated.
> > > 
> > > 
> > > 
> > > I'm able to use CPU_ISSET to the same effect, but obviously I'd rather use CPU_COUNT.  Suggestions?
> > > 
> > 
> > Show the minimal example demonstrating the issue, specify the version
> > of the system and which you use.  My guess is that you did not added
> > #include <sys/types.h> before including sys/cpuset.h.

diff --git a/sys/sys/types.h b/sys/sys/types.h
index 4a66a4e..4dfd8ef 100644
--- a/sys/sys/types.h
+++ b/sys/sys/types.h
@@ -290,9 +290,6 @@ typedef	_Bool	bool;
  * The following are all things that really shouldn't exist in this header,
  * since its purpose is to provide typedefs, not miscellaneous doodads.
  */
-#if __BSD_VISIBLE
-
-#include <sys/select.h>
 
 #ifdef __POPCNT__
 #define	__bitcount64(x)	__builtin_popcountll((__uint64_t)(x))
@@ -356,6 +353,10 @@ __bitcount64(__uint64_t _x)
 #define	__bitcount(x)	__bitcount32((unsigned int)(x))
 #endif
 
+#if __BSD_VISIBLE
+
+#include <sys/select.h>
+
 /*
  * minor() gives a cookie instead of an index since we don't want to
  * change the meanings of bits 0-15 or waste time and space shifting