84a3aadf0f
Reapplication of 7339c0f782d5c70e0928f8991b0c05338a90c84c with a fix for a crash involving arrays without a size expression. Clang supports VLAs in C++ as an extension, but we currently only warn on their use when you pass -Wvla, -Wvla-extension, or -pedantic. However, VLAs as they're expressed in C have been considered by WG21 and rejected, are easy to use accidentally to the surprise of users (e.g., https://ddanilov.me/default-non-standard-features/), and they have potential security implications beyond constant-size arrays (https://wiki.sei.cmu.edu/confluence/display/c/ARR32-C.+Ensure+size+arguments+for+variable+length+arrays+are+in+a+valid+range). C++ users should strongly consider using other functionality such as std::vector instead. This seems like sufficiently compelling evidence to warn users about VLA use by default in C++ modes. This patch enables the -Wvla-extension diagnostic group in C++ language modes by default, and adds the warning group to -Wall in GNU++ language modes. The warning is still opt-in in C language modes, where support for VLAs is somewhat less surprising to users. RFC: https://discourse.llvm.org/t/rfc-diagnosing-use-of-vlas-in-c/73109 Fixes https://github.com/llvm/llvm-project/issues/62836 Differential Revision: https://reviews.llvm.org/D156565
43 lines
1.2 KiB
C++
43 lines
1.2 KiB
C++
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -O0 -verify -Wno-vla %s
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// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -pedantic-errors -O0 -verify=pe %s
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// expected-no-diagnostics
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extern "C" int printf(const char*, ...);
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static int N;
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struct S {
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S() __attribute__ ((nothrow)) { printf("%d: S()\n", ++N); }
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~S() __attribute__ ((nothrow)) { printf("%d: ~S()\n", N--); }
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int n[17];
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};
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void print(int n, int a, int b, int c, int d) {
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printf("n=%d\n,sizeof(S)=%d\nsizeof(array_t[0][0])=%d\nsizeof(array_t[0])=%d\nsizeof(array_t)=%d\n",
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n, a, b, c, d);
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if (n == 2) throw(n);
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}
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void test(int n) {
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S array_t[n][n+1]; // pe-error 2{{variable length arrays in C++ are a Clang extension}} pe-note 2{{parameter}} pe-note@-1 2{{here}}
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int sizeof_S = sizeof(S);
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int sizeof_array_t_0_0 = sizeof(array_t[0][0]);
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int sizeof_array_t_0 = sizeof(array_t[0]);
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int sizeof_array_t = sizeof(array_t);
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print(n, sizeof_S, sizeof_array_t_0_0, sizeof_array_t_0, sizeof_array_t);
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}
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int main()
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{
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try {
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test(2);
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} catch(int e) {
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printf("exception %d\n", e);
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}
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try {
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test(3);
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} catch(int e) {
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printf("exception %d", e);
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}
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}
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