Re: libgomp crash fix

[Bruno Haible <bruno at clisp dot org>]

Jakub Jelinek wrote on 2006-11-20:
> I think you should use -pthread instead of -lpthread here (and put it into
> CFLAGS too temporarily), to make it more portable, or try all of nothing,
> -pthread and -lpthread, i.e. add a for loop trying to compile and run the
> program 3 times.

Here's a revised patch that does this: first find out which flags are
needed to build a program that uses pthread_create(), then see whether
libc actually supports __thread.

I've verified that this patch causes the configuration to print
  checking whether the target supports thread-local storage... no
in the situation of bug #28468.


2006-12-17  Bruno Haible  <bruno@clisp.org>

	* config/tls.m4 (GCC_CHECK_TLS): Also check whether the libc supports
	TLS via __thread.

--- config/tls.m4.bak	2006-12-04 12:13:07.000000000 +0100
+++ config/tls.m4	2006-12-17 18:02:30.000000000 +0100
@@ -13,9 +13,60 @@
 	AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
 		      [have_tls=yes], [have_tls=no],[]),
 	[have_tls=yes])
-      LDFLAGS="$save_LDFLAGS"],
+      LDFLAGS="$save_LDFLAGS"
+      if test $have_tls = yes; then
+        dnl So far, the binutils and the compiler support TLS.
+        dnl Also check whether the libc supports TLS, i.e. whether a variable
+        dnl with __thread linkage has a different address in different threads.
+        dnl First, find the thread_CFLAGS necessary for linking a program that
+        dnl calls pthread_create.
+        save_CFLAGS="$CFLAGS"
+        thread_CFLAGS=failed
+        for flag in '' '-pthread' '-lpthread'; do
+          CFLAGS="$flag $save_CFLAGS"
+          AC_LINK_IFELSE(
+            [AC_LANG_PROGRAM(
+               [#include <pthread.h>
+                void *g(void *d) { return NULL; }],
+               [pthread_t t; pthread_create(&t,NULL,g,NULL);])],
+            [thread_CFLAGS="$flag"])
+          if test "X$thread_CFLAGS" != Xfailed; then
+            break
+          fi
+        done
+        CFLAGS="$save_CFLAGS"
+        if test "X$thread_CFLAGS" != Xfailed; then
+          CFLAGS="$thread_CFLAGS $save_CFLAGS"
+          AC_RUN_IFELSE(
+            [AC_LANG_PROGRAM(
+               [#include <pthread.h>
+                __thread int a;
+                static int *a_in_other_thread;
+                static void *
+                thread_func (void *arg)
+                {
+                  a_in_other_thread = &a;
+                  return (void *)0;
+                }],
+               [pthread_t thread;
+                void *thread_retval;
+                int *a_in_main_thread;
+                if (pthread_create (&thread, (pthread_attr_t *)0,
+                                    thread_func, (void *)0))
+                  return 2;
+                a_in_main_thread = &a;
+                if (pthread_join (thread, &thread_retval))
+                  return 3;
+                return (a_in_other_thread == a_in_main_thread);])],
+             [have_tls=yes], [have_tls=no])
+          CFLAGS="$save_CFLAGS"
+        fi
+      fi],
       [have_tls=no],
-      [AC_COMPILE_IFELSE([__thread int foo;], [have_tls=yes], [have_tls=no])]
+      [dnl This is the cross-compiling case. Assume libc supports TLS if the
+       dnl binutils and the compiler do.
+       AC_COMPILE_IFELSE([__thread int foo;], [have_tls=yes], [have_tls=no])
+      ]
     )])
   if test "$enable_tls $have_tls" = "yes yes"; then
     AC_DEFINE(HAVE_TLS, 1,