gh-94808:Improve coverage of PyObject_Print

[MonadChains]

This PR improves the coverage of the function PyObject_Print:

cpython/Objects/object.c

Line 256 in 29b391b

PyObject_Print(PyObject *op, FILE *fp, int flags)

The coverage achieved is the following:

I couldn't hit line 294, I'm open for discussion on how to do this.

• Issue: Metabug: Improving C-level coverage #94808

[nanjekyejoannah]

The change seems useful but some tests are still failing.

[MonadChains]

Hi @nanjekyejoannah,
The test that fails is the address sanitizer one with the following error: SUMMARY: AddressSanitizer: heap-use-after-free Modules/_testcapimodule.c:2083 in pyobject_print_noref_object

This happens in this function:

cpython/Modules/_testcapimodule.c

Lines 2055 to 2083 in 25c24e4

	static PyObject *
	pyobject_print_noref_object(PyObject *self, PyObject *args)
	{
	PyObject *test_string;
	PyObject *filename;
	FILE *fp;
	char correct_string[100];
	test_string = PyUnicode_FromString("Spam spam spam");
	Py_DECREF(test_string);
	snprintf(correct_string, 100, "<refcnt %zd at %p>", Py_REFCNT(test_string), (void *)test_string);
	if (!PyArg_UnpackTuple(args, "call_pyobject_print", 1, 1, &filename)) {
	return NULL;
	}
	fp = _Py_fopen_obj(filename, "w+");
	if (PyObject_Print(test_string, fp, 0) < 0){
	fclose(fp);
	return NULL;
	}
	fclose(fp);
	return PyUnicode_FromString(correct_string);
	}

This function tests the behaviour of PyObject_Print in case it receives a object with reference counter set to 0:

cpython/Objects/object.c

Lines 274 to 278 in bded5ed

	if (Py_REFCNT(op) <= 0) {
	Py_BEGIN_ALLOW_THREADS
	fprintf(fp, "<refcnt %zd at %p>", Py_REFCNT(op), (void *)op);
	Py_END_ALLOW_THREADS
	}

I guess the address sanitizer doesn't like that a deallocated object is used after Py_DECREF. Do you have any tips on solving this problem?

[MonadChains]

Hi @nanjekyejoannah, the pipeline now is working. I've fixed the failing test so the overall coverage achieved by PR is still the same.

[nanjekyejoannah]

@MonadChains I will thoroughly look in a day or two.

[encukou]

After a year, I've rebased onto the current main branch, moved the tests to where they'd be added today, and fixed a few things I would have pointed out in a review.

Does this look good?

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 MacOS M1 Refleaks NoGIL 3.x has failed when building commit 90c3c68.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1368/builds/630) and take a look at the build logs.
4. Check if the failure is related to this commit (90c3c68) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1368/builds/630

Failed tests:

• test_capi

Test leaking resources:

• test_capi: memory blocks
• test_capi: references

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 55, done.        
remote: Counting objects:   1% (1/55)        
remote: Counting objects:   3% (2/55)        
remote: Counting objects:   5% (3/55)        
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remote: Counting objects:  98% (54/55)        
remote: Counting objects: 100% (55/55)        
remote: Counting objects: 100% (55/55), done.        
remote: Compressing objects:   5% (1/18)        
remote: Compressing objects:  11% (2/18)        
remote: Compressing objects:  16% (3/18)        
remote: Compressing objects:  22% (4/18)        
remote: Compressing objects:  27% (5/18)        
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remote: Compressing objects: 100% (18/18)        
remote: Compressing objects: 100% (18/18), done.        
remote: Total 31 (delta 26), reused 15 (delta 13), pack-reused 0        
From https://github.com/python/cpython
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HEAD is now at 90c3c68a65 gh-94808:Improve coverage of PyObject_Print (GH-98749)
Switched to and reset branch 'main'

In file included from ./Modules/_tkinter.c:52:
In file included from /opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/tk.h:99:
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:131:21: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        int (*free_private)();  /* called to free private storage */
                           ^
                            void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:334:33: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        struct _XImage *(*create_image)();
                                       ^
                                        void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:453:23: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        XID (*resource_alloc)(); /* allocator function */
                             ^
                              void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:471:20: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        int (*synchandler)();   /* Synchronization handler */
                          ^
                           void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:496:24: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        Bool (*event_vec[128])();  /* vector for wire to event */
                              ^
                               void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:497:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        Status (*wire_vec[128])(); /* vector for event to wire */
                               ^
                                void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:509:20: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        Bool (**error_vec)();      /* vector for wire to error */
                          ^
                           void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:522:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        int (*savedsynchandler)(); /* user synchandler when Xlib usurps */
                               ^
                                void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:1053:24: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
typedef void (*XIMProc)();
                       ^
                        void
In file included from ./Modules/tkappinit.c:17:
In file included from /opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/tk.h:99:
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:131:21: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        int (*free_private)();  /* called to free private storage */
                           ^
                            void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:334:33: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        struct _XImage *(*create_image)();
                                       ^
                                        void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:453:23: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        XID (*resource_alloc)(); /* allocator function */
                             ^
                              void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:471:20: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        int (*synchandler)();   /* Synchronization handler */
                          ^
                           void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:496:24: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        Bool (*event_vec[128])();  /* vector for wire to event */
                              ^
                               void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:497:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        Status (*wire_vec[128])(); /* vector for event to wire */
                               ^
                                void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:509:20: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        Bool (**error_vec)();      /* vector for wire to error */
                          ^
                           void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:522:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
        int (*savedsynchandler)(); /* user synchandler when Xlib usurps */
                               ^
                                void
/opt/homebrew/Cellar/tcl-tk/8.6.13_5/include/tcl-tk/X11/Xlib.h:1053:24: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
typedef void (*XIMProc)();
                       ^
                        void
9 warnings generated.
9 warnings generated.

make: *** [buildbottest] Error 2