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

pablogsal · pablogsal · commit 170075a741c0 · 2025-01-23T14:42:13.000Z
Signed-off-by: Pablo Galindo &lt;pablogsal@gmail.com&gt;
diff --git a/Include/internal/pycore_debug_offsets.h b/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
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
@@ -117,6 +117,7 @@ typedef struct _Py_AsyncioModuleDebugOffsets {
     } asyncio_thread_state;
 } Py_AsyncioModuleDebugOffsets;
 
+PyAPI_DATA(Py_AsyncioModuleDebugOffsets) AsyncioDebug;
 GENERATE_DEBUG_SECTION(AsyncioDebug, Py_AsyncioModuleDebugOffsets AsyncioDebug)
     = {.asyncio_task_object = {
            .size = sizeof(TaskObj),
diff --git a/Modules/_testexternalinspection.c b/Modules/_testexternalinspection.c
@@ -414,7 +414,11 @@ 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;
 }
 
 

Original file line number	Diff line number	Diff line change
`@@ -414,7 +414,11 @@ get_py_runtime(pid_t pid)`
`414`	`414`	`static uintptr_t`
`415`	`415`	`get_async_debug(pid_t pid)`
`416`	`416`	`{`
`417`		`- return search_map_for_section(pid, "AsyncioDebug", "_asyncio.cpython");`
	`417`	`+ uintptr_t result = search_map_for_section(pid, "AsyncioDebug", "_asyncio.cpython");`
	`418`	`+ if (result == 0 && !PyErr_Occurred()) {`
	`419`	`+ PyErr_SetString(PyExc_RuntimeError, "Cannot find AsyncioDebug section");`
	`420`	`+ }`
	`421`	`+ return result;`
`418`	`422`	`}`
`419`	`423`
`420`	`424`