3eba28d1fd
This is a follow-up patch to #96475 to detect dangling assignments for C++ pointer-like objects (classes annotated with the `[[gsl::Pointer]]`). Fixes #63310. Similar to the behavior for built-in pointer types, if a temporary owner (`[[gsl::Owner]]`) object is assigned to a pointer-like class object, and this temporary object is destroyed at the end of the full assignment expression, the assignee pointer is considered dangling. In such cases, clang will emit a warning: ``` /tmp/t.cpp:7:20: warning: object backing the pointer my_string_view will be destroyed at the end of the full-expression [-Wdangling-assignment-gsl] 7 | my_string_view = CreateString(); | ^~~~~~~~~~~~~~ 1 warning generated. ``` This new warning is `-Wdangling-assignment-gsl`. It is initially disabled, but I intend to enable it by default in clang 20. I have initially tested this patch on our internal codebase, and it has identified many use-after-free bugs, primarily related to `string_view`.
40 lines
1.8 KiB
C++
40 lines
1.8 KiB
C++
// RUN: %clang_cc1 -verify -std=c++11 -Wdangling-assignment-gsl %s
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using T = int[];
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void f() {
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int *p = &(int&)(int&&)0; // expected-warning {{temporary whose address is used as value of local variable 'p' will be destroyed at the end of the full-expression}}
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p = &(int&)(int&&)0; // expected-warning {{object backing the pointer p will be destroyed at the end of the full-expression}}
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int *q = (int *const &)T{1, 2, 3}; // expected-warning {{temporary whose address is used as value of local variable 'q' will be destroyed at the end of the full-expression}}
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q = (int *const &)T{1, 2, 3}; // expected-warning {{object backing the pointer q will be destroyed at the end of the full-expression}}
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// FIXME: We don't warn here because the 'int*' temporary is not const, but
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// it also can't have actually changed since it was created, so we could
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// still warn.
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int *r = (int *&&)T{1, 2, 3};
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// FIXME: The wording of this warning is not quite right. There are two
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// temporaries here: an 'int* const' temporary that points to the array, and
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// is lifetime-extended, and an array temporary that the pointer temporary
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// points to, which doesn't live long enough.
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int *const &s = (int *const &)T{1, 2, 3}; // expected-warning {{temporary bound to local reference 's' will be destroyed at the end of the full-expression}}
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}
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// PR38355
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void g() {
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const int a[] = {a[0]};
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const int b[] = {a[0]};
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}
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namespace std {
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// std::basic_string has a hard-coded gsl::owner attr.
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struct basic_string {
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const char* c_str();
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};
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} // namespace std
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void test(const char* a) {
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// verify we're emitting the `-Wdangling-assignment-gsl` warning.
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a = std::basic_string().c_str(); // expected-warning {{object backing the pointer a will be destroyed at the end of the full-expression}}
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}
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