Compiler warnings on string comparisons in _testcapi

[iritkatriel]

./Modules/_testcapimodule.c:226:18: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
        assert(v != UNINITIALIZED_PTR);
                 ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
./Modules/_testcapimodule.c:238:14: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(k == UNINITIALIZED_PTR);
             ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
./Modules/_testcapimodule.c:239:14: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(v == UNINITIALIZED_PTR);
             ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
4 warnings generated.
./Modules/_testcapi/dict.c:289:16: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(key == UNINITIALIZED_PTR);
               ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
./Modules/_testcapi/dict.c:290:18: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(value == UNINITIALIZED_PTR);
                 ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
2 warnings generated.
./Modules/_testcapi/exceptions.c:129:17: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(type != UNINITIALIZED_PTR);
                ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
./Modules/_testcapi/exceptions.c:130:18: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(value != UNINITIALIZED_PTR);
                 ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)
                        ^
./Modules/_testcapi/exceptions.c:131:15: warning: result of comparison against a string literal is unspecified (use an explicit string comparison function instead) [-Wstring-compare]
    assert(tb != UNINITIALIZED_PTR);
              ^  ~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/assert.h:99:25: note: expanded from macro 'assert'
    (__builtin_expect(!(e), 0) ? __assert_rtn(__func__, __ASSERT_FILE_NAME, __LINE__, #e) : (void)0)

Linked PRs

• gh-109469: Silence compiler warnings on string comparisons in _testcapi #109533
• [3.12] gh-109469: Silence compiler warnings on string comparisons in _testcapi (GH-109533) #109558

[sunmy2019]

Changing UNINITIALIZED_PTR to an invalid address literal should resolve this.

such as #define UNINITIALIZED_PTR 0xcdcdcdcdcdcdcdcd on x64.

[erlend-aasland]

cc. @serhiy-storchaka

[serhiy-storchaka]

The point was to use valid address. On some platforms, not all bit combinations can be interpreted as address, and interpreting them as address can even lead to crash.

Does the following change help with warning?

-#define UNINITIALIZED_PTR ((void *)"uninitialized")
+static const char uninitialized[] = "uninitialized";
+#define UNINITIALIZED_PTR ((void *)uninitialized)

[iritkatriel]

Does the following change help with warning?

-#define UNINITIALIZED_PTR ((void *)"uninitialized")
+static const char uninitialized[] = "uninitialized";
+#define UNINITIALIZED_PTR ((void *)uninitialized)

Yes.