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gh-124064: Fix some -Wconversion warnings #124174

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Merged
merged 4 commits into from
Sep 17, 2024
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gh-124064: Fix some -Wconversion warnings #124174

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6899ab1
gh-124064: Fix some -Wconversion warnings
vstinner Sep 17, 2024
622cc5c
Update warnings ignore files
vstinner Sep 17, 2024
ee637e6
revert pegen
vstinner Sep 17, 2024
ae8406c
update import.c warnings count
vstinner Sep 17, 2024
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2 changes: 1 addition & 1 deletion Include/internal/pycore_gc.h
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Expand Up @@ -227,7 +227,7 @@ static inline void _PyGC_CLEAR_FINALIZED(PyObject *op) {
_PyObject_CLEAR_GC_BITS(op, _PyGC_BITS_FINALIZED);
#else
PyGC_Head *gc = _Py_AS_GC(op);
gc->_gc_prev &= ~_PyGC_PREV_MASK_FINALIZED;
gc->_gc_prev &= ~(uintptr_t)_PyGC_PREV_MASK_FINALIZED;
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I think it might be better to make the _PyGC_PREV_MASK_FINALIZED literal unsigned.

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I tried #define _PyGC_PREV_MASK_FINALIZED 1U but the code got miscompiled and failed.

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Ugh... you're right. It won't get sign extended in that case.

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I wrote a different fix in the following change: #124177

-#define _PyGC_PREV_MASK_FINALIZED 1
+#define _PyGC_PREV_MASK_FINALIZED ((uintptr_t)1)

It seems to work like that. I also prefer to fix the constant declaration rather than having to cast the constant every time.

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FYI, I started a discussion about -Wsign-conversion in the #gsoc-security-project Discord channel. It seems to me that adding these explicit casts in many places to address -Wsign-conversion does not make the code less bug prone and probably does the opposite.

In this case, we now have a tighter coupling between the _PyGC_PREV_MASK_FINALIZED and the type of _gc_prev and _gc_next. That seems worse to me than before where we relied on the implicit sign conversion.

For example, if we hypothetically changed _gc_prev to uint64_t, the code would now be incorrect.

#endif
}

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2 changes: 1 addition & 1 deletion Include/internal/pycore_list.h
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Expand Up @@ -45,7 +45,7 @@ _Py_memory_repeat(char* dest, Py_ssize_t len_dest, Py_ssize_t len_src)
Py_ssize_t copied = len_src;
while (copied < len_dest) {
Py_ssize_t bytes_to_copy = Py_MIN(copied, len_dest - copied);
memcpy(dest + copied, dest, bytes_to_copy);
memcpy(dest + copied, dest, (size_t)bytes_to_copy);
copied += bytes_to_copy;
}
}
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4 changes: 2 additions & 2 deletions Include/internal/pycore_stackref.h
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Expand Up @@ -98,7 +98,7 @@ typedef union _PyStackRef {
static inline PyObject *
PyStackRef_AsPyObjectBorrow(_PyStackRef stackref)
{
PyObject *cleared = ((PyObject *)((stackref).bits & (~Py_TAG_BITS)));
PyObject *cleared = ((PyObject *)((stackref).bits & (~(uintptr_t)Py_TAG_BITS)));
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Same here

return cleared;
}
#else
Expand Down Expand Up @@ -133,7 +133,7 @@ _PyStackRef_FromPyObjectSteal(PyObject *obj)
{
// Make sure we don't take an already tagged value.
assert(((uintptr_t)obj & Py_TAG_BITS) == 0);
int tag = (obj == NULL || _Py_IsImmortal(obj)) ? (Py_TAG_DEFERRED) : Py_TAG_PTR;
unsigned int tag = (obj == NULL || _Py_IsImmortal(obj)) ? (Py_TAG_DEFERRED) : Py_TAG_PTR;
return ((_PyStackRef){.bits = ((uintptr_t)(obj)) | tag});
}
# define PyStackRef_FromPyObjectSteal(obj) _PyStackRef_FromPyObjectSteal(_PyObject_CAST(obj))
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1 change: 0 additions & 1 deletion Tools/build/.warningignore_macos
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Expand Up @@ -6,7 +6,6 @@
Include/internal/mimalloc/mimalloc/internal.h 4
Include/internal/pycore_backoff.h 1
Include/internal/pycore_dict.h 2
Include/internal/pycore_gc.h 1
Include/internal/pycore_long.h 2
Include/internal/pycore_object.h 4
Modules/_asynciomodule.c 3
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4 changes: 0 additions & 4 deletions Tools/build/.warningignore_ubuntu
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Expand Up @@ -19,10 +19,7 @@ Include/internal/pycore_asdl.h 1
Include/internal/pycore_backoff.h 3
Include/internal/pycore_blocks_output_buffer.h 1
Include/internal/pycore_dict.h 2
Include/internal/pycore_gc.h 1
Include/internal/pycore_gc.h 1
Include/internal/pycore_interp.h 1
Include/internal/pycore_list.h 1
Include/internal/pycore_long.h 3
Include/internal/pycore_object.h 4
Include/internal/pycore_obmalloc.h 1
Expand Down Expand Up @@ -233,7 +230,6 @@ Python/generated_cases.c.h 27
Python/generated_cases.c.h 27
Python/getargs.c 7
Python/hashtable.c 1
Python/import.c 6
Python/import.c 7
Python/initconfig.c 11
Python/instrumentation.c 43
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