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m4: fix gl_TIMER_TIME() detection of threads on uClibc The timer_time.m4 gl_TIMER_TIME function determines which libraries need to be linked to get access to the timer function, generally -lrt for Linux systems. On platforms where threads are used, librt typically uses thread functions from libpthread. However, the test to determine whether the platform has thread or not is incorrect: it assumes that if the C library is uClibc, then threads are not available. This is actually not true: uClibc has configurable thread support, and when thread support is available, librt calls libpthread functions. This is important when static linking is used, because otherwise only -lrt is used at link time, which fails because librt calls undefined thread functions. Both -lrt and -lpthread must be passed. This problem is fixed by making the uClibc thread detection a bit smarter, thanks to the usage of the __HAS_NO_THREADS__ macro defined in <bits/uClibc_config.h>, which itself is included by <features.h>. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Signed-off-by: Eric Blake <eblake@redhat.com>
author Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
date Sat, 22 Feb 2014 00:41:38 +0100
parents 344018b6e5d7
children
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# timer_time.m4 serial 2
dnl Copyright (C) 2011-2014 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

# Check for timer_settime, and set LIB_TIMER_TIME.

AC_DEFUN([gl_TIMER_TIME],
[
  dnl Based on clock_time.m4. See details there.

  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
  AC_REQUIRE([gl_THREADLIB])

  LIB_TIMER_TIME=
  AC_SUBST([LIB_TIMER_TIME])
  gl_saved_libs=$LIBS
    AC_SEARCH_LIBS([timer_settime], [rt posix4],
                   [test "$ac_cv_search_timer_settime" = "none required" ||
                    LIB_TIMER_TIME=$ac_cv_search_timer_settime])
    dnl GLIBC uses threads to emulate posix timers when kernel support
    dnl is not available (like Linux < 2.6 or when used with kFreeBSD)
    dnl Now the pthread lib is linked automatically in the normal case,
    dnl but when linking statically, it needs to be explicitly specified.
    AC_EGREP_CPP([Thread],
      [
#include <features.h>
#ifdef __GNU_LIBRARY__
 #if ((__GLIBC__ == 2 && __GLIBC_MINOR__ >= 2) || (__GLIBC__ > 2)) \
     && !(__UCLIBC__ && __HAS_NO_THREADS__)
  Thread emulation available
 #endif
#endif
      ],
      [LIB_TIMER_TIME="$LIB_TIMER_TIME $LIBMULTITHREAD"])
    AC_CHECK_FUNCS([timer_settime])
  LIBS=$gl_saved_libs
])