Re: [patch] Fix TLS access for -static -pthread

[Jan Kratochvil <jan.kratochvil@redhat.com>]

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On Tue, 20 May 2014 17:10:03 +0200, Tom Tromey wrote:
> This bit of code (and another like it later on) should have a longer
> comment, probably at least including the link above, but also some text
> about how this is a hack but why it is ok.

I have put there:
+      /* This code path handles the case of -static -pthread executables:
+	 https://sourceware.org/ml/libc-help/2014-03/msg00024.html
+	 For older GNU libc r_debug.r_map is NULL.  For GNU libc after
+	 PR libc/16831 due to GDB PR threads/16954 LOAD_MODULE is also NULL.
+	 The constant number 1 depends on GNU __libc_setup_tls
+	 initialization of l_tls_modid to 1.  */


> Otherwise this is ok.

Reposting with the comment update.


Jan

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gdb/
2014-05-21  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix TLS access for -static -pthread.
	* linux-thread-db.c (struct thread_db_info): Add td_thr_tlsbase_p.
	(try_thread_db_load_1): Initialize it.
	(thread_db_get_thread_local_address): Call it if LM is zero.
	* target.c (target_translate_tls_address): Remove LM_ADDR zero check.
	* target.h (struct target_ops) (to_get_thread_local_address): Add
	load_module_addr comment.

gdb/gdbserver/
2014-05-21  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix TLS access for -static -pthread.
	* gdbserver/thread-db.c (struct thread_db): Add td_thr_tlsbase_p.
	(thread_db_get_tls_address): Call it if LOAD_MODULE is zero.
	(thread_db_load_search, try_thread_db_load_1): Initialize it.

gdb/testsuite/
2014-04-10  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix TLS access for -static -pthread.
	* gdb.threads/staticthreads.c <HAVE_TLS> (tlsvar): New.
	<HAVE_TLS> (thread_function, main): Initialize it.
	* gdb.threads/staticthreads.exp: Try gdb_compile_pthreads for $have_tls.
	Add clean_restart.
	<$have_tls != "">: Check TLSVAR.

diff --git a/gdb/gdbserver/thread-db.c b/gdb/gdbserver/thread-db.c
index ae0d191..3ea0cc3 100644
--- a/gdb/gdbserver/thread-db.c
+++ b/gdb/gdbserver/thread-db.c
@@ -88,6 +88,9 @@ struct thread_db
   td_err_e (*td_thr_tls_get_addr_p) (const td_thrhandle_t *th,
 				     psaddr_t map_address,
 				     size_t offset, psaddr_t *address);
+  td_err_e (*td_thr_tlsbase_p) (const td_thrhandle_t *th,
+				unsigned long int modid,
+				psaddr_t *base);
   const char ** (*td_symbol_list_p) (void);
 };
 
@@ -503,7 +506,10 @@ thread_db_get_tls_address (struct thread_info *thread, CORE_ADDR offset,
   if (thread_db == NULL || !thread_db->all_symbols_looked_up)
     return TD_ERR;
 
-  if (thread_db->td_thr_tls_get_addr_p == NULL)
+  /* If td_thr_tls_get_addr is missing rather do not expect td_thr_tlsbase
+     could work.  */
+  if (thread_db->td_thr_tls_get_addr_p == NULL
+      || (load_module == 0 && thread_db->td_thr_tlsbase_p == NULL))
     return -1;
 
   lwp = get_thread_lwp (thread);
@@ -514,12 +520,28 @@ thread_db_get_tls_address (struct thread_info *thread, CORE_ADDR offset,
 
   saved_inferior = current_inferior;
   current_inferior = thread;
-  /* Note the cast through uintptr_t: this interface only works if
-     a target address fits in a psaddr_t, which is a host pointer.
-     So a 32-bit debugger can not access 64-bit TLS through this.  */
-  err = thread_db->td_thr_tls_get_addr_p (&lwp->th,
-					  (psaddr_t) (uintptr_t) load_module,
-					  offset, &addr);
+
+  if (load_module != 0)
+    {
+      /* Note the cast through uintptr_t: this interface only works if
+	 a target address fits in a psaddr_t, which is a host pointer.
+	 So a 32-bit debugger can not access 64-bit TLS through this.  */
+      err = thread_db->td_thr_tls_get_addr_p (&lwp->th,
+					     (psaddr_t) (uintptr_t) load_module,
+					      offset, &addr);
+    }
+  else
+    {
+      /* This code path handles the case of -static -pthread executables:
+	 https://sourceware.org/ml/libc-help/2014-03/msg00024.html
+	 For older GNU libc r_debug.r_map is NULL.  For GNU libc after
+	 PR libc/16831 due to GDB PR threads/16954 LOAD_MODULE is also NULL.
+	 The constant number 1 depends on GNU __libc_setup_tls
+	 initialization of l_tls_modid to 1.  */
+      err = thread_db->td_thr_tlsbase_p (&lwp->th, 1, &addr);
+      addr = (char *) addr + offset;
+    }
+
   current_inferior = saved_inferior;
   if (err == TD_OK)
     {
@@ -571,6 +593,7 @@ thread_db_load_search (void)
   tdb->td_ta_set_event_p = &td_ta_set_event;
   tdb->td_ta_event_getmsg_p = &td_ta_event_getmsg;
   tdb->td_thr_tls_get_addr_p = &td_thr_tls_get_addr;
+  tdb->td_thr_tlsbase_p = &td_thr_tlsbase;
 
   return 1;
 }
@@ -639,6 +662,7 @@ try_thread_db_load_1 (void *handle)
   CHK (0, tdb->td_ta_set_event_p = dlsym (handle, "td_ta_set_event"));
   CHK (0, tdb->td_ta_event_getmsg_p = dlsym (handle, "td_ta_event_getmsg"));
   CHK (0, tdb->td_thr_tls_get_addr_p = dlsym (handle, "td_thr_tls_get_addr"));
+  CHK (0, tdb->td_thr_tlsbase_p = dlsym (handle, "td_thr_tlsbase"));
 
 #undef CHK
 
diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index ca614a3..c0f7b1a 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -196,6 +196,9 @@ struct thread_db_info
   td_err_e (*td_thr_tls_get_addr_p) (const td_thrhandle_t *th,
 				     psaddr_t map_address,
 				     size_t offset, psaddr_t *address);
+  td_err_e (*td_thr_tlsbase_p) (const td_thrhandle_t *th,
+				unsigned long int modid,
+				psaddr_t *base);
 };
 
 /* List of known processes using thread_db, and the required
@@ -799,6 +802,7 @@ try_thread_db_load_1 (struct thread_db_info *info)
   info->td_ta_event_getmsg_p = dlsym (info->handle, "td_ta_event_getmsg");
   info->td_thr_event_enable_p = dlsym (info->handle, "td_thr_event_enable");
   info->td_thr_tls_get_addr_p = dlsym (info->handle, "td_thr_tls_get_addr");
+  info->td_thr_tlsbase_p = dlsym (info->handle, "td_thr_tlsbase");
 
   if (thread_db_find_new_threads_silently (inferior_ptid) != 0)
     {
@@ -1811,21 +1815,39 @@ thread_db_get_thread_local_address (struct target_ops *ops,
 
       info = get_thread_db_info (ptid_get_pid (ptid));
 
-      /* glibc doesn't provide the needed interface.  */
-      if (!info->td_thr_tls_get_addr_p)
-	throw_error (TLS_NO_LIBRARY_SUPPORT_ERROR,
-		     _("No TLS library support"));
-
-      /* Caller should have verified that lm != 0.  */
-      gdb_assert (lm != 0);
-
       /* Finally, get the address of the variable.  */
-      /* Note the cast through uintptr_t: this interface only works if
-	 a target address fits in a psaddr_t, which is a host pointer.
-	 So a 32-bit debugger can not access 64-bit TLS through this.  */
-      err = info->td_thr_tls_get_addr_p (&thread_info->private->th,
-					 (psaddr_t)(uintptr_t) lm,
-					 offset, &address);
+      if (lm != 0)
+	{
+	  /* glibc doesn't provide the needed interface.  */
+	  if (!info->td_thr_tls_get_addr_p)
+	    throw_error (TLS_NO_LIBRARY_SUPPORT_ERROR,
+			 _("No TLS library support"));
+
+	  /* Note the cast through uintptr_t: this interface only works if
+	     a target address fits in a psaddr_t, which is a host pointer.
+	     So a 32-bit debugger can not access 64-bit TLS through this.  */
+	  err = info->td_thr_tls_get_addr_p (&thread_info->private->th,
+					     (psaddr_t)(uintptr_t) lm,
+					     offset, &address);
+	}
+      else
+	{
+	  /* If glibc doesn't provide the needed interface throw an error
+	     that LM is zero - normally cases it should not be.  */
+	  if (!info->td_thr_tlsbase_p)
+	    throw_error (TLS_LOAD_MODULE_NOT_FOUND_ERROR,
+			 _("TLS load module not found"));
+
+	  /* This code path handles the case of -static -pthread executables:
+	     https://sourceware.org/ml/libc-help/2014-03/msg00024.html
+	     For older GNU libc r_debug.r_map is NULL.  For GNU libc after
+	     PR libc/16831 due to GDB PR threads/16954 LOAD_MODULE is also NULL.
+	     The constant number 1 depends on GNU __libc_setup_tls
+	     initialization of l_tls_modid to 1.  */
+	  err = info->td_thr_tlsbase_p (&thread_info->private->th,
+					1, &address);
+	  address = (char *) address + offset;
+	}
 
 #ifdef THREAD_DB_HAS_TD_NOTALLOC
       /* The memory hasn't been allocated, yet.  */
diff --git a/gdb/target.c b/gdb/target.c
index d08e2ea..71292d3 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -757,10 +757,6 @@ target_translate_tls_address (struct objfile *objfile, CORE_ADDR offset)
 	  /* Fetch the load module address for this objfile.  */
 	  lm_addr = gdbarch_fetch_tls_load_module_address (target_gdbarch (),
 	                                                   objfile);
-	  /* If it's 0, throw the appropriate exception.  */
-	  if (lm_addr == 0)
-	    throw_error (TLS_LOAD_MODULE_NOT_FOUND_ERROR,
-			 _("TLS load module not found"));
 
 	  addr = target->to_get_thread_local_address (target, ptid,
 						      lm_addr, offset);
diff --git a/gdb/target.h b/gdb/target.h
index 23a7566..9371529 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -605,7 +605,8 @@ struct target_ops
        thread-local storage for the thread PTID and the shared library
        or executable file given by OBJFILE.  If that block of
        thread-local storage hasn't been allocated yet, this function
-       may return an error.  */
+       may return an error.  LOAD_MODULE_ADDR may be zero for statically
+       linked multithreaded inferiors.  */
     CORE_ADDR (*to_get_thread_local_address) (struct target_ops *ops,
 					      ptid_t ptid,
 					      CORE_ADDR load_module_addr,
diff --git a/gdb/testsuite/gdb.threads/staticthreads.c b/gdb/testsuite/gdb.threads/staticthreads.c
index e834d7f..5c8eabe 100644
--- a/gdb/testsuite/gdb.threads/staticthreads.c
+++ b/gdb/testsuite/gdb.threads/staticthreads.c
@@ -28,10 +28,17 @@
 
 sem_t semaphore;
 
+#ifdef HAVE_TLS
+__thread int tlsvar;
+#endif
+
 void *
 thread_function (void *arg)
 {
-  printf ("Thread executing\n");
+#ifdef HAVE_TLS
+  tlsvar = 2;
+#endif
+  printf ("Thread executing\n"); /* tlsvar-is-set */
   while (sem_wait (&semaphore) != 0)
     {
       if (errno != EINTR)
@@ -57,6 +64,9 @@ main (int argc, char **argv)
       return -1;
     }
 
+#ifdef HAVE_TLS
+  tlsvar = 1;
+#endif
 
   /* Create a thread, wait for it to complete.  */
   {
diff --git a/gdb/testsuite/gdb.threads/staticthreads.exp b/gdb/testsuite/gdb.threads/staticthreads.exp
index 80b0ba8..9fa625a 100644
--- a/gdb/testsuite/gdb.threads/staticthreads.exp
+++ b/gdb/testsuite/gdb.threads/staticthreads.exp
@@ -22,11 +22,16 @@
 standard_testfile
 set static_flag "-static"
 
-if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" \
-	 executable \
-	 [list debug "additional_flags=${static_flag}" \
-	     ]] != "" } {
-    return -1
+foreach have_tls { "-DHAVE_TLS" "" } {
+    if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" \
+	     executable \
+	     [list debug "additional_flags=${static_flag} ${have_tls}" \
+		 ]] == "" } {
+	break
+    }
+    if { $have_tls == "" } {
+	return -1
+    }
 }
 
 clean_restart ${binfile}
@@ -89,3 +94,18 @@ gdb_test_multiple "quit" "$test" {
         pass "$test"
     }
 }
+clean_restart ${binfile}
+
+
+if { "$have_tls" != "" } {
+    if ![runto_main] {
+	return -1
+    }
+    gdb_breakpoint [gdb_get_line_number "tlsvar-is-set"]
+    gdb_continue_to_breakpoint "tlsvar-is-set" ".* tlsvar-is-set .*"
+    gdb_test "p tlsvar" " = 2" "tlsvar in thread"
+    gdb_test "thread 1" ".*"
+    # Unwind from pthread_join.
+    gdb_test "up 10" " in main .*"
+    gdb_test "p tlsvar" " = 1" "tlsvar in main"
+}