gh-141770: Annotate anonymous mmap usage if "-X dev" is used

Doc/whatsnew/3.15.rst

@@ -1253,6 +1253,12 @@ Build changes
  modules that are missing or packaged separately.
  (Contributed by Stan Ulbrych and Petr Viktorin in :gh:`139707`.)
 
+* Annotating anonymous mmap usage is now supported if Linux kernel supports
+ :manpage:`PR_SET_VMA_ANON_NAME <PR_SET_VMA(2const)>` (Linux 5.17 or newer).
+ Annotations are visible in ``/proc/<pid>/maps`` if the kernel supports the feature
+ and :option:`-X dev <-X>` is passed to the Python or Python is built in :ref:`debug mode <debug-build>`.
+ (Contributed by Donghee Na in :gh:`141770`)
+
 
 Porting to Python 3.15
 ======================

Include/internal/pycore_mmap.h

@@ -0,0 +1,45 @@
+#ifndef Py_INTERNAL_MMAP_H
+#define Py_INTERNAL_MMAP_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+# error "this header requires Py_BUILD_CORE define"
+#endif
+
+#include "pycore_pystate.h"
+
+#if defined(HAVE_PR_SET_VMA_ANON_NAME) && defined(__linux__)
+# include <linux/prctl.h>
+# include <sys/prctl.h>
+#endif
+
+#if defined(HAVE_PR_SET_VMA_ANON_NAME) && defined(__linux__)
+static inline void
+_PyAnnotateMemoryMap(void *addr, size_t size, const char *name)
+{
+#ifndef Py_DEBUG
+ if (!_Py_GetConfig()->dev_mode) {
+ return;
+ }
+#endif
+ assert(strlen(name) < 80);
+ int old_errno = errno;
+ prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, (unsigned long)addr, size, name);
+ /* Ignore errno from prctl */
+ /* See: https://bugzilla.redhat.com/show_bug.cgi?id=2302746 */
+ errno = old_errno;
+}
+#else
+static inline void
+_PyAnnotateMemoryMap(void *Py_UNUSED(addr), size_t Py_UNUSED(size), const char *Py_UNUSED(name))
+{
+}
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+#endif // !Py_INTERNAL_MMAP_H

Makefile.pre.in

@@ -1378,6 +1378,7 @@ PYTHON_HEADERS= \
  $(srcdir)/Include/internal/pycore_long.h \
  $(srcdir)/Include/internal/pycore_memoryobject.h \
  $(srcdir)/Include/internal/pycore_mimalloc.h \
+ $(srcdir)/Include/internal/pycore_mmap.h \
  $(srcdir)/Include/internal/pycore_modsupport.h \
  $(srcdir)/Include/internal/pycore_moduleobject.h \
  $(srcdir)/Include/internal/pycore_namespace.h \

Misc/NEWS.d/next/Core_and_Builtins/2025-11-29-18-14-28.gh-issue-141770.JURnvg.rst

@@ -0,0 +1,2 @@
+Annotate anonymous mmap usage only when supported by the
+Linux kernel and if ``-X dev`` is used or Python is built in debug mode. Patch by Donghee Na.

Modules/_ctypes/malloc_closure.c

@@ -14,6 +14,7 @@
 # endif
 #endif
 #include "ctypes.h"
+#include "pycore_mmap.h" // _PyAnnotateMemoryMap()
 
 /* BLOCKSIZE can be adjusted. Larger blocksize will take a larger memory
  overhead, but allocate less blocks from the system. It may be that some
@@ -74,14 +75,16 @@ static void more_core(void)
  if (item == NULL)
  return;
 #else
+ size_t mem_size = count * sizeof(ITEM);
  item = (ITEM *)mmap(NULL,
-count * sizeof(ITEM),
+mem_size,
  PROT_READ | PROT_WRITE | PROT_EXEC,
  MAP_PRIVATE | MAP_ANONYMOUS,
  -1,
  0);
  if (item == (void *)MAP_FAILED)
  return;
+ _PyAnnotateMemoryMap(item, mem_size, "cpython:ctypes");
 #endif
 
 #ifdef MALLOC_CLOSURE_DEBUG

Modules/mmapmodule.c

@@ -26,6 +26,7 @@
 #include "pycore_abstract.h" // _Py_convert_optional_to_ssize_t()
 #include "pycore_bytesobject.h" // _PyBytes_Find()
 #include "pycore_fileutils.h" // _Py_stat_struct
+#include "pycore_mmap.h" // _PyAnnotateMemoryMap()
 #include "pycore_weakref.h" // FT_CLEAR_WEAKREFS()
 
 #include <stddef.h> // offsetof()
@@ -1951,6 +1952,7 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
  PyErr_SetFromErrno(PyExc_OSError);
  return NULL;
  }
+ _PyAnnotateMemoryMap(m_obj->data, map_size, "cpython:mmap");
  m_obj->access = (access_mode)access;
  return (PyObject *)m_obj;
 }

Objects/obmalloc.c

@@ -2,6 +2,7 @@
 
 #include "Python.h"
 #include "pycore_interp.h" // _PyInterpreterState_HasFeature
+#include "pycore_mmap.h" // _PyAnnotateMemoryMap()
 #include "pycore_object.h" // _PyDebugAllocatorStats() definition
 #include "pycore_obmalloc.h"
 #include "pycore_obmalloc_init.h"
@@ -467,6 +468,7 @@ _PyMem_ArenaAlloc(void *Py_UNUSED(ctx), size_t size)
  if (ptr == MAP_FAILED)
  return NULL;
  assert(ptr != NULL);
+ _PyAnnotateMemoryMap(ptr, size, "cpython:pymalloc");
  return ptr;
 #else
  return malloc(size);

PCbuild/pythoncore.vcxproj

@@ -277,6 +277,7 @@
  <ClInclude Include="..\Include\internal\pycore_llist.h" />
  <ClInclude Include="..\Include\internal\pycore_lock.h" />
  <ClInclude Include="..\Include\internal\pycore_long.h" />
+ <ClInclude Include="..\Include\internal\pycore_mmap.h" />
  <ClInclude Include="..\Include\internal\pycore_modsupport.h" />
  <ClInclude Include="..\Include\internal\pycore_moduleobject.h" />
  <ClInclude Include="..\Include\internal\pycore_namespace.h" />

PCbuild/pythoncore.vcxproj.filters

@@ -735,6 +735,9 @@
  <ClInclude Include="..\Include\internal\pycore_long.h">
  <Filter>Include\internal</Filter>
  </ClInclude>
+ <ClInclude Include="..\Include\internal\pycore_mmap.h">
+ <Filter>Include\internal</Filter>
+ </ClInclude>
  <ClInclude Include="..\Include\internal\pycore_modsupport.h">
  <Filter>Include\internal</Filter>
  </ClInclude>

Python/jit.c

@@ -16,6 +16,7 @@
 #include "pycore_intrinsics.h"
 #include "pycore_list.h"
 #include "pycore_long.h"
+#include "pycore_mmap.h"
 #include "pycore_opcode_metadata.h"
 #include "pycore_opcode_utils.h"
 #include "pycore_optimizer.h"
@@ -75,6 +76,9 @@ jit_alloc(size_t size)
  int prot = PROT_READ | PROT_WRITE;
  unsigned char *memory = mmap(NULL, size, prot, flags, -1, 0);
  int failed = memory == MAP_FAILED;
+ if (!failed) {
+ _PyAnnotateMemoryMap(memory, size, "cpython:jit");
+ }
 #endif
  if (failed) {
  jit_error("unable to allocate memory");

Python/perf_jit_trampoline.c

@@ -61,6 +61,7 @@
 #include "pycore_ceval.h" // _PyPerf_Callbacks
 #include "pycore_frame.h"
 #include "pycore_interp.h"
+#include "pycore_mmap.h" // _PyAnnotateMemoryMap()
 #include "pycore_runtime.h" // _PyRuntime
 
 #ifdef PY_HAVE_PERF_TRAMPOLINE
@@ -1085,6 +1086,7 @@ static void* perf_map_jit_init(void) {
  close(fd);
  return NULL; // Memory mapping failed
  }
+ _PyAnnotateMemoryMap(perf_jit_map_state.mapped_buffer, page_size, "cpython:perf_jit_trampoline");
 #endif
 
  perf_jit_map_state.mapped_size = page_size;

Python/perf_trampoline.c

@@ -132,6 +132,7 @@ any DWARF information available for them).
 #include "Python.h"
 #include "pycore_ceval.h" // _PyPerf_Callbacks
 #include "pycore_interpframe.h" // _PyFrame_GetCode()
+#include "pycore_mmap.h" // _PyAnnotateMemoryMap()
 #include "pycore_runtime.h" // _PyRuntime
 
 
@@ -290,6 +291,7 @@ new_code_arena(void)
  perf_status = PERF_STATUS_FAILED;
  return -1;
  }
+ _PyAnnotateMemoryMap(memory, mem_size, "cpython:perf_trampoline");
  void *start = &_Py_trampoline_func_start;
  void *end = &_Py_trampoline_func_end;
  size_t code_size = end - start;

configure.ac

@@ -5587,6 +5587,13 @@ AC_CHECK_DECLS([UT_NAMESIZE],
  [],
  [@%:@include <utmp.h>])
 
+AC_CHECK_DECLS([PR_SET_VMA_ANON_NAME],
+ [AC_DEFINE([HAVE_PR_SET_VMA_ANON_NAME], [1],
+ [Define if you have the 'PR_SET_VMA_ANON_NAME' constant.])],
+ [],
+ [@%:@include <linux/prctl.h>
+ @%:@include <sys/prctl.h>])
+
 # check for openpty, login_tty, and forkpty
 
 AC_CHECK_FUNCS([openpty], [],

pyconfig.h.in

@@ -228,6 +228,10 @@
 /* Define to 1 if you have the <db.h> header file. */
 #undef HAVE_DB_H
 
+/* Define to 1 if you have the declaration of 'PR_SET_VMA_ANON_NAME', and to 0
+ if you don't. */
+#undef HAVE_DECL_PR_SET_VMA_ANON_NAME
+
 /* Define to 1 if you have the declaration of 'RTLD_DEEPBIND', and to 0 if you
  don't. */
 #undef HAVE_DECL_RTLD_DEEPBIND
@@ -996,6 +1000,9 @@
 /* Define if your compiler supports function prototype */
 #undef HAVE_PROTOTYPES
 
+/* Define if you have the 'PR_SET_VMA_ANON_NAME' constant. */
+#undef HAVE_PR_SET_VMA_ANON_NAME
+
 /* Define to 1 if you have the 'pthread_condattr_setclock' function. */
 #undef HAVE_PTHREAD_CONDATTR_SETCLOCK