Re: Hanging conftest

[Eric Blake]

On 11/28/2013 07:34 AM, Eric Blake wrote:

[back from holidays, so reviving this thread]

>> Michal, since you have the environment to test this, can you rerun:
>>
>> ./configure MALLOC_CHECK_=2
>>
>> and see if the hang goes away?  If so, then I know how to patch gnulib
>> to ensure that this particular environment variable is always set for
>> each conftest that tries to tickle a known glibc memory corruption bug.

Michal complained that setting MALLOC_CHECK_ for the entire configure
slowed things down.

> 
> On IRC, Michal confirmed that this hack patch helped avoid a conftest hang:
> 
> diff --git i/m4/regex.m4 w/m4/regex.m4
> index 424ae33..b0eed19 100644
> --- i/m4/regex.m4
> +++ w/m4/regex.m4
>  -41,6 +41,15 @@ AC_DEFUN([gl_REGEX],
>              # include <unistd.h>
>              # include <signal.h>
>              #endif
> +#ifdef __linux__
> +#include <execinfo.h>
> +static void __attribute__ ((constructor))
> +init_backtrace()
> +{
> +   void *bt[10];
> +   backtrace (bt, 10);
> +}
> +#endif
>            ]],
>            [[int result = 0;
>              static struct re_pattern_buffer regex;

He also said this approach worked:

diff --git i/m4/regex.m4 w/m4/regex.m4
index 424ae33..0089c08 100644
--- i/m4/regex.m4
+++ w/m4/regex.m4
@@ -1,4 +1,4 @@
-# serial 64
+# serial 65

 # Copyright (C) 1996-2001, 2003-2013 Free Software Foundation, Inc.
 #
@@ -28,6 +28,7 @@ AC_DEFUN([gl_REGEX],
     # If cross compiling, assume the test would fail and use the included
     # regex.c.
     AC_CHECK_DECLS_ONCE([alarm])
+    AC_CHECK_HEADERS_ONCE([malloc.h])
     AC_CACHE_CHECK([for working re_compile_pattern],
                    [gl_cv_func_re_compile_pattern_working],
       [AC_RUN_IFELSE(
@@ -41,6 +42,9 @@ AC_DEFUN([gl_REGEX],
             # include <unistd.h>
             # include <signal.h>
             #endif
+            #if HAVE_MALLOC_H
+            # include <malloc.h>
+            #endif
           ]],
           [[int result = 0;
             static struct re_pattern_buffer regex;
@@ -49,11 +53,17 @@ AC_DEFUN([gl_REGEX],
             const char *s;
             struct re_registers regs;

+            /* Some builds of glibc go into an infinite loop on this
+               test.  Use alarm to force death, and mallopt to avoid
+               malloc recursion in diagnosing the corrupted heap. */
 #if HAVE_DECL_ALARM
-            /* Some builds of glibc go into an infinite loop on this
test.  */
             signal (SIGALRM, SIG_DFL);
             alarm (2);
 #endif
+#ifdef M_CHECK_ACTION
+            mallopt(M_CHECK_ACTION, 2);
+#endif
+
             if (setlocale (LC_ALL, "en_US.UTF-8"))
               {
                 {


Any preferences on which one I should use in gnulib?

> 
> But then he reported that the check for a working sleep() hung, which
> makes me wonder if SIGALRM/alarm() semantics are broken on his system.

No idea what was happening here, but it's a separate issue to debug if
it is still happening.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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