[Mono-devel-list] [PATCH] issue with libmono.so and dlopen

[Miguel de Icaza]

Hello,

   Did you compile your own Mono?  You might want to disable the TLS
support in your Mono to work around these issues.

> Hi,
> 
> I ran into a problem with dlopen and libmono.so. It appears
> that the one and only __thread variable of libgc will
> get the tls-model "global-dynamic", which doesn't seem to
> be compatible with dlopen(3). I don't know whether this is
> a bug or a "by design" feature.
> 
> Mini uses  __attribute__((tls_model("local-exec"))) for
> __thread variables, if applicable, so I just added
> the same code block I found in mono-compiler.h
> to libgc/pthread_support.c
> 
> The patch will probably speed-up the GC a little bit, although
> I did't profile it.
> 
> I'm not happy with the attached patch because it duplicates
> code between mini and libgc, so I'd provide another patch,
> if you guys would accept this solution:
> 
> configure.is probes whether the GCC switch -ftls-model
> is working. If yes, -ftls-model=local-exec will be added
> to the CFLAGS of Mono and libgc. MONO_FAST_TLS can be
> obsoleted.
> 
> Rob
> 
> ps: the attached "foo.c" is a test case for the problem.
> Plain text document attachment (tls.diff)
> Index: libgc/pthread_support.c
> ===================================================================
> --- libgc/pthread_support.c	(revision 46453)
> +++ libgc/pthread_support.c	(working copy)
> @@ -168,11 +168,23 @@
>  
>  /* We don't really support thread-local allocation with DBG_HDRS_ALL */
>  
> +#if USE_COMPILER_TLS_ATTR
> +#if defined(PIC) && defined(__x86_64__)
> +#define COMPILER_TLS_ATTR 
> +#elif defined (__powerpc__)
> +#define COMPILER_TLS_ATTR 
> +#else
> +#define COMPILER_TLS_ATTR  __attribute__((tls_model("local-exec")))
> +#endif
> +#else
> +#define COMPILER_TLS_ATTR
> +#endif
> +
>  static
>  #ifdef USE_COMPILER_TLS
>    __thread
>  #endif
> -GC_key_t GC_thread_key;
> +GC_key_t GC_thread_key COMPILER_TLS_ATTR;
>  
>  static GC_bool keys_initialized;
>  
> Index: configure.in
> ===================================================================
> --- configure.in	(revision 46453)
> +++ configure.in	(working copy)
> @@ -1598,7 +1598,10 @@
>  	AC_TRY_COMPILE([static __thread int foo __attribute__((tls_model("initial-exec")));], [
>  		], [
>  			AC_MSG_RESULT(yes)
> -			AC_DEFINE(HAVE_TLS_MODEL_ATTR, 1, [tld_model available])
> +			AC_DEFINE(HAVE_TLS_MODEL_ATTR, 1, [tls_model available])
> +			# Pass the information to libgc as well
> +			CPPFLAGS="$CPPFLAGS -DUSE_COMPILER_TLS_ATTR"
> +			export CPPFLAGS
>  		], [
>  			AC_MSG_RESULT(no)
>  	])
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-- 
Miguel de Icaza <miguel at ximian.com>