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bpo-46323: Reduce stack usage of ctypes python callback function. #31224

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Merged
corona10 merged 6 commits into from
Feb 9, 2022
Merged

bpo-46323: Reduce stack usage of ctypes python callback function. #31224

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3754856
bpo-46323: Fix stack allocation to avoid stackoverflow
corona10 Feb 8, 2022
cbab14b
bpo-46323: Address code review
corona10 Feb 9, 2022
4aaf1e6
bpo-46323: Fix Windows ARM64
corona10 Feb 9, 2022
71a82b5
bpo-46323: Address code review
corona10 Feb 9, 2022
07c12ff
bpo-46323: Address code review
corona10 Feb 9, 2022
f4a276f
bpo-46323: Add NEWS entry
corona10 Feb 9, 2022
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-02-10-02-29-12.bpo-46323.HK_cs0.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:mod:`ctypes` now allocates memory on the stack instead of on the heap
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@sweeneyde sweeneyde Feb 9, 2022

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There was no heap allocation directly before this PR, and there will be no heap allocation after, right? It's just eliminating that dead code path.

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@corona10 corona10 Feb 9, 2022 •
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@sweeneyde Yeah but this is the result of bpo-46323

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@corona10 corona10 Feb 9, 2022

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Victor and I decided to add NEWS entry for all this change at this moment.
Theoretically, we had to add NEWS entry at the first PR, but it's too late.

to pass arguments while calling a Python callback function.
Patch by Dong-hee Na.
35 changes: 13 additions & 22 deletions Modules/_ctypes/callbacks.c
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Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,18 @@

#include <stdbool.h>

#ifdef MS_WIN32
# include <malloc.h>
#endif

#include <ffi.h>
#include "ctypes.h"

#ifdef HAVE_ALLOCA_H
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@corona10 corona10 Feb 8, 2022

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Same workaroud

cpython/Modules/_ctypes/callproc.c

Lines 80 to 84 in 06e1701

#include "ctypes.h"
#ifdef HAVE_ALLOCA_H
/* AIX needs alloca.h for alloca() */
#include <alloca.h>
#endif

/* AIX needs alloca.h for alloca() */
#include <alloca.h>
#endif

/**************************************************************/

static void
Expand Down Expand Up @@ -147,32 +156,17 @@ static void _CallPythonObject(void *mem,
void **pArgs)
{
PyObject *result = NULL;
PyObject **args = NULL;
Py_ssize_t i = 0, j = 0, nargs = 0;
PyObject *error_object = NULL;
int *space;
PyGILState_STATE state = PyGILState_Ensure();

assert(PyTuple_Check(converters));
nargs = PyTuple_GET_SIZE(converters);
/* Hm. What to return in case of error?
For COM, 0xFFFFFFFF seems better than 0.
*/
if (nargs < 0) {
PrintError("BUG: PySequence_Length");
goto Done;
}

PyObject *args_stack[CTYPES_MAX_ARGCOUNT];
if (nargs <= CTYPES_MAX_ARGCOUNT) {
args = args_stack;
}
else {
args = PyMem_Malloc(nargs * sizeof(PyObject *));
if (args == NULL) {
PyErr_NoMemory();
goto Done;
}
assert(nargs <= CTYPES_MAX_ARGCOUNT);
PyObject **args = NULL;
if (nargs > 0) {
args = alloca(nargs * sizeof(PyObject *));
}

PyObject **cnvs = PySequence_Fast_ITEMS(converters);
Expand Down Expand Up @@ -309,9 +303,6 @@ static void _CallPythonObject(void *mem,
for (j = 0; j < i; j++) {
Py_DECREF(args[j]);
}
if (args != args_stack) {
PyMem_Free(args);
}
PyGILState_Release(state);
}

Expand Down
6 changes: 1 addition & 5 deletions Modules/_ctypes/callproc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1160,11 +1160,7 @@ PyObject *_ctypes_callproc(PPROC pProc,
return NULL;
}

args = (struct argument *)alloca(sizeof(struct argument) * argcount);
if (!args) {
PyErr_NoMemory();
return NULL;
}
args = alloca(sizeof(struct argument) * argcount);
memset(args, 0, sizeof(struct argument) * argcount);
argtype_count = argtypes ? PyTuple_GET_SIZE(argtypes) : 0;
#ifdef MS_WIN32
Expand Down