libs/libc/tls: Add a per-thread __emutls_get_address().

libs/libc/tls/CMakeLists.txt

@@ -34,4 +34,21 @@ if(NOT CONFIG_TLS_NCLEANUP EQUAL 0)
   list(APPEND SRCS tls_cleanup.c)
 endif()
 
+# A GCC toolchain configured with --disable-tls compiles a thread_local variable
+# into a call to __emutls_get_address(), and the libgcc of such a toolchain
+# keeps one copy of the variable for the whole program. Replace it with the
+# implementation of tls_emutls.c, which keeps one copy per thread. The symbols
+# of libgcc have external linkage and are pulled into the link of some
+# configurations whatever the order of the archives is, so redirect the calls
+# with --wrap rather than define the same names.
+if("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU"
+   AND NOT CONFIG_SCHED_THREAD_LOCAL
+   AND NOT CONFIG_DISABLE_PTHREAD
+   AND NOT CONFIG_TLS_NELEM EQUAL 0
+   AND NOT CONFIG_TLS_TASK_NELEM EQUAL 0)
+  list(APPEND SRCS tls_emutls.c)
+  target_link_options(nuttx PRIVATE -Wl,--wrap=__emutls_get_address
+                      -Wl,--wrap=__emutls_register_common)
+endif()
+
 target_sources(c PRIVATE ${SRCS})

libs/libc/tls/Make.defs

@@ -34,6 +34,25 @@ ifneq ($(CONFIG_TLS_NCLEANUP),0)
 CSRCS += tls_cleanup.c
 endif
 
+# A GCC toolchain configured with --disable-tls compiles a thread_local
+# variable into a call to __emutls_get_address(), and the libgcc of such a
+# toolchain keeps one copy of the variable for the whole program.  Replace it
+# with the implementation of tls_emutls.c, which keeps one copy per thread.
+# The --wrap options that redirect the calls are in tools/Config.mk because
+# the link runs from arch/<arch>/src, which does not include this file.  The
+# conditions must stay the same in both places.
+ifeq ($(CONFIG_ARCH_TOOLCHAIN_GNU)$(CONFIG_ARCH_TOOLCHAIN_CLANG)$(CONFIG_ARCH_TOOLCHAIN_ARMCLANG)$(CONFIG_ARCH_TOOLCHAIN_GHS),y)
+ifneq ($(CONFIG_SCHED_THREAD_LOCAL),y)
+ifneq ($(CONFIG_DISABLE_PTHREAD),y)
+ifneq ($(CONFIG_TLS_NELEM),0)
+ifneq ($(CONFIG_TLS_TASK_NELEM),0)
+CSRCS += tls_emutls.c
+endif
+endif
+endif
+endif
+endif
+
 # Include tls build support
 
 DEPPATH += --dep-path tls

libs/libc/tls/tls_emutls.c

@@ -0,0 +1,310 @@
+/****************************************************************************
+ * libs/libc/tls/tls_emutls.c
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * This version uses a cascaded task_tls + pthread_key approach:
+ *   - task_tls index stored in obj->loc.offset (system-level, permanent)
+ *   - task_tls value stores pthread_key+1 per task group (0 = not created)
+ *   - pthread_getspecific/pthread_setspecific for per-thread data
+ *
+ * This avoids the problem of pthread keys being per-task-group while
+ * __emutls_object is global.
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <assert.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <nuttx/lib/lib.h>
+#include <nuttx/tls.h>
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/* The types and the layout of the control object follow the definitions of
+ * emutls.c in libgcc, because the compiler emits the object and this file
+ * only reads it.
+ */
+
+typedef unsigned int word __attribute__((mode(word)));
+
+struct __emutls_object
+{
+  word size;
+  word align;
+  union
+  {
+    uintptr_t offset;  /* task_tls index + 1 (0 = not allocated) */
+    FAR void *ptr;
+  } loc;
+  FAR void *templ;
+};
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/* Serializes the allocation of the task local storage index of a variable
+ * and the creation of the pthread key of a task group.
+ */
+
+static pthread_mutex_t g_emutls_lock = PTHREAD_MUTEX_INITIALIZER;
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: emutls_destroy
+ *
+ * Description:
+ *   Frees the copy of a variable when the thread that used it exits.  It is
+ *   the destructor of the pthread key of the variable.
+ *
+ * Input Parameters:
+ *   ptr - The copy of the variable of the exiting thread
+ *
+ ****************************************************************************/
+
+static void emutls_destroy(FAR void *ptr)
+{
+  lib_free(ptr);
+}
+
+/****************************************************************************
+ * Name: emutls_alloc
+ *
+ * Description:
+ *   Allocates the copy of a variable for the calling thread and gives it
+ *   the initial value of the variable, which is the template of the object
+ *   or zero when the variable has none.
+ *
+ * Input Parameters:
+ *   obj - The control object of the variable
+ *
+ * Returned Value:
+ *   The copy of the variable, or NULL when the allocation fails.
+ *
+ ****************************************************************************/
+
+static FAR void *emutls_alloc(FAR struct __emutls_object *obj)
+{
+  FAR void *ret;
+
+  if (obj->align > sizeof(FAR void *))
+    {
+      ret = lib_memalign(obj->align, obj->size);
+    }
+  else
+    {
+      ret = lib_malloc(obj->size);
+    }
+
+  if (ret != NULL)
+    {
+      if (obj->templ != NULL)
+        {
+          memcpy(ret, obj->templ, obj->size);
+        }
+      else
+        {
+          memset(ret, 0, obj->size);
+        }
+    }
+
+  return ret;
+}
+
+/****************************************************************************
+ * Name: emutls_key
+ *
+ * Description:
+ *   Returns the pthread key that holds the copies of the variable in the
+ *   task group of the caller, and creates it on the first use.
+ *
+ * Input Parameters:
+ *   tlsindex - The task local storage index of the variable
+ *
+ * Returned Value:
+ *   The pthread key of the variable in this task group.  Panics when the
+ *   key cannot be created, because the caller that the compiler emits has
+ *   no way to report the failure.
+ *
+ ****************************************************************************/
+
+static pthread_key_t emutls_key(int tlsindex)
+{
+  pthread_key_t key;
+  uintptr_t value;
+
+  /* Ensure this task group has a pthread key */
+
+  value = task_tls_get_value(tlsindex);
+  if (value == 0)
+    {
+      pthread_mutex_lock(&g_emutls_lock);
+      value = task_tls_get_value(tlsindex);
+      if (value == 0)
+        {
+          if (pthread_key_create(&key, emutls_destroy) != 0)
+            {
+              pthread_mutex_unlock(&g_emutls_lock);
+              PANIC();
+            }
+
+          value = (uintptr_t)key + 1;
+          if (task_tls_set_value(tlsindex, value) < 0)
+            {
+              pthread_key_delete(key);
+              pthread_mutex_unlock(&g_emutls_lock);
+              PANIC();
+            }
+        }
+
+      pthread_mutex_unlock(&g_emutls_lock);
+    }
+
+  return (pthread_key_t)(value - 1);
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: __wrap___emutls_get_address
+ *
+ * Description:
+ *   Return a per-thread pointer for the TLS variable described by obj.
+ *   Overrides libgcc's single-threaded __emutls_get_address via --wrap
+ *   linker option. Uses cascaded task_tls + pthread_key for per-thread
+ *   isolation across task groups.
+ *
+ * Input Parameters:
+ *   arg - Pointer to the __emutls_object descriptor (compiler-generated)
+ *
+ * Returned Value:
+ *   Pointer to the per-thread TLS variable storage. Calls PANIC() on
+ *   allocation failure since the compiler-generated caller cannot handle
+ *   NULL.
+ *
+ ****************************************************************************/
+
+FAR void *__wrap___emutls_get_address(FAR void *arg)
+{
+  FAR struct __emutls_object *obj = arg;
+  pthread_key_t key;
+  FAR void *ret;
+
+  /* Ensure this object has a task_tls index allocated */
+
+  if (obj->loc.offset == 0)
+    {
+      pthread_mutex_lock(&g_emutls_lock);
+      if (obj->loc.offset == 0)
+        {
+          int tlsindex = task_tls_alloc(NULL);
+
+          if (tlsindex < 0)
+            {
+              pthread_mutex_unlock(&g_emutls_lock);
+              PANIC();
+            }
+
+          obj->loc.offset = (uintptr_t)tlsindex + 1;
+        }
+
+      pthread_mutex_unlock(&g_emutls_lock);
+    }
+
+  key = emutls_key((int)(obj->loc.offset - 1));
+
+  /* Get or allocate per-thread storage */
+
+  ret = pthread_getspecific(key);
+  if (ret == NULL)
+    {
+      ret = emutls_alloc(obj);
+      if (ret == NULL)
+        {
+          PANIC();
+        }
+
+      if (pthread_setspecific(key, ret) != 0)
+        {
+          lib_free(ret);
+          PANIC();
+        }
+    }
+
+  return ret;
+}
+
+/****************************************************************************
+ * Name: __wrap___emutls_register_common
+ *
+ * Description:
+ *   Register a TLS common symbol. Called by GCC during startup
+ *   (.init_array, single-threaded context) for thread_local variables
+ *   with common linkage. Updates the object's size, alignment, and
+ *   initialization template using largest-wins semantics.
+ *
+ * Input Parameters:
+ *   arg   - Pointer to the __emutls_object descriptor
+ *   size  - Size of the TLS variable
+ *   align - Alignment requirement of the TLS variable
+ *   templ - Pointer to initialization template in .tdata (may be NULL)
+ *
+ * Returned Value:
+ *   None.
+ *
+ ****************************************************************************/
+
+void __wrap___emutls_register_common(FAR void *arg, word size, word align,
+                                     FAR void *templ)
+{
+  FAR struct __emutls_object *obj = arg;
+
+  if (obj->size < size)
+    {
+      obj->size = size;
+      obj->templ = NULL;
+    }
+
+  if (obj->align < align)
+    {
+      obj->align = align;
+    }
+
+  if (templ != NULL && size == obj->size)
+    {
+      obj->templ = templ;
+    }
+}

tools/Config.mk

@@ -895,3 +895,21 @@ LOWER_CASE = $(call ULMAP,$(LOWERMAP),$(1))
 ifeq ($(CONFIG_ITERABLE_SECTIONS_LINKER_INSERT),y)
   ARCHSCRIPT += $(TOPDIR)$(DELIM)include$(DELIM)nuttx$(DELIM)linker$(DELIM)common-insert.ld
 endif
+
+# Like the fragment above, the --wrap options that redirect the thread_local
+# accessor to libs/libc/tls/tls_emutls.c have to be here rather than next to
+# the source, because the link runs from arch/<arch>/src, which includes this
+# file but not the Make.defs of libs/.  The conditions must stay the same as
+# in libs/libc/tls/Make.defs.
+
+ifeq ($(CONFIG_ARCH_TOOLCHAIN_GNU)$(CONFIG_ARCH_TOOLCHAIN_CLANG)$(CONFIG_ARCH_TOOLCHAIN_ARMCLANG)$(CONFIG_ARCH_TOOLCHAIN_GHS),y)
+ifneq ($(CONFIG_SCHED_THREAD_LOCAL),y)
+ifneq ($(CONFIG_DISABLE_PTHREAD),y)
+ifneq ($(CONFIG_TLS_NELEM),0)
+ifneq ($(CONFIG_TLS_TASK_NELEM),0)
+  LDFLAGS += --wrap=__emutls_get_address --wrap=__emutls_register_common
+endif
+endif
+endif
+endif
+endif