gh-129223: Do not allow the compiler to optimise away symbols for debug sections

Signed-off-by: Pablo Galindo <[email protected]>

Author: pablogsal

Include/internal/pycore_debug_offsets.h

@@ -17,31 +17,32 @@ extern "C" {
 
 // Macros to burn global values in custom sections so out-of-process
 // profilers can locate them easily.
-
-#define GENERATE_DEBUG_SECTION(name, declaration) \
-    _GENERATE_DEBUG_SECTION_WINDOWS(name)         \
-    _GENERATE_DEBUG_SECTION_APPLE(name)           \
-    declaration                                   \
-    _GENERATE_DEBUG_SECTION_LINUX(name)
+#define GENERATE_DEBUG_SECTION(name, declaration)     \
+   _GENERATE_DEBUG_SECTION_WINDOWS(name)            \
+   _GENERATE_DEBUG_SECTION_APPLE(name)              \
+   declaration                                      \
+   _GENERATE_DEBUG_SECTION_LINUX(name)
 
 #if defined(MS_WINDOWS)
 #define _GENERATE_DEBUG_SECTION_WINDOWS(name)                       \
-    _Pragma(Py_STRINGIFY(section(Py_STRINGIFY(name), read, write))) \
-    __declspec(allocate(Py_STRINGIFY(name)))
+   _Pragma(Py_STRINGIFY(section(Py_STRINGIFY(name), read, write))) \
+   __declspec(allocate(Py_STRINGIFY(name)))
 #else
 #define _GENERATE_DEBUG_SECTION_WINDOWS(name)
 #endif
 
 #if defined(__APPLE__)
 #define _GENERATE_DEBUG_SECTION_APPLE(name) \
-    __attribute__((section(SEG_DATA "," Py_STRINGIFY(name))))
+   __attribute__((section(SEG_DATA "," Py_STRINGIFY(name))))      \
+   __attribute__((used))
 #else
 #define _GENERATE_DEBUG_SECTION_APPLE(name)
 #endif
 
 #if defined(__linux__) && (defined(__GNUC__) || defined(__clang__))
 #define _GENERATE_DEBUG_SECTION_LINUX(name) \
-    __attribute__((section("." Py_STRINGIFY(name))))
+   __attribute__((section("." Py_STRINGIFY(name))))               \
+   __attribute__((used))
 #else
 #define _GENERATE_DEBUG_SECTION_LINUX(name)
 #endif
@@ -327,6 +328,29 @@ typedef struct _Py_DebugOffsets {
     }, \
 }
 
+// Collection of extern declarations for debug offset symbols in extension
+// modules. These declarations are here to ensure the compiler marks them
+// as external symbols. Unfortunately there isn't a cross platform way to
+// do this elegantly withing the compilation unit itself as different compilers
+// complain in different ways.
+
+typedef struct _Py_AsyncioModuleDebugOffsets {
+    struct _asyncio_task_object {
+        uint64_t size;
+        uint64_t task_name;
+        uint64_t task_awaited_by;
+        uint64_t task_is_task;
+        uint64_t task_awaited_by_is_set;
+        uint64_t task_coro;
+    } asyncio_task_object;
+    struct _asyncio_thread_state {
+        uint64_t size;
+        uint64_t asyncio_running_loop;
+        uint64_t asyncio_running_task;
+    } asyncio_thread_state;
+} Py_AsyncioModuleDebugOffsets;
+PyAPI_DATA(Py_AsyncioModuleDebugOffsets) AsyncioDebug;
+
 
 #ifdef __cplusplus
 }

Modules/_asynciomodule.c

@@ -101,22 +101,6 @@ typedef struct {
 #   define ASYNCIO_STATE_UNLOCK(state) ((void)state)
 #endif
 
-typedef struct _Py_AsyncioModuleDebugOffsets {
-    struct _asyncio_task_object {
-        uint64_t size;
-        uint64_t task_name;
-        uint64_t task_awaited_by;
-        uint64_t task_is_task;
-        uint64_t task_awaited_by_is_set;
-        uint64_t task_coro;
-    } asyncio_task_object;
-    struct _asyncio_thread_state {
-        uint64_t size;
-        uint64_t asyncio_running_loop;
-        uint64_t asyncio_running_task;
-    } asyncio_thread_state;
-} Py_AsyncioModuleDebugOffsets;
-
 GENERATE_DEBUG_SECTION(AsyncioDebug, Py_AsyncioModuleDebugOffsets AsyncioDebug)
     = {.asyncio_task_object = {
            .size = sizeof(TaskObj),

Modules/_testexternalinspection.c

@@ -59,22 +59,6 @@
 #    define HAVE_PROCESS_VM_READV 0
 #endif
 
-struct _Py_AsyncioModuleDebugOffsets {
-    struct _asyncio_task_object {
-        uint64_t size;
-        uint64_t task_name;
-        uint64_t task_awaited_by;
-        uint64_t task_is_task;
-        uint64_t task_awaited_by_is_set;
-        uint64_t task_coro;
-    } asyncio_task_object;
-    struct _asyncio_thread_state {
-        uint64_t size;
-        uint64_t asyncio_running_loop;
-        uint64_t asyncio_running_task;
-    } asyncio_thread_state;
-};
-
 #if defined(__APPLE__) && TARGET_OS_OSX
 static uintptr_t
 return_section_address(
@@ -414,7 +398,11 @@ get_py_runtime(pid_t pid)
 static uintptr_t
 get_async_debug(pid_t pid)
 {
-    return search_map_for_section(pid, "AsyncioDebug", "_asyncio.cpython");
+    uintptr_t result = search_map_for_section(pid, "AsyncioDebug", "_asyncio.cpython");
+    if (result == 0 && !PyErr_Occurred()) {
+        PyErr_SetString(PyExc_RuntimeError, "Cannot find AsyncioDebug section");
+    }
+    return result;
 }