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When `-ftrivial-auto-var-init=` is enabled, allocas unconditionally receive auto-initialization since [1]. In certain cases, it turns out, this is causing problems. For example, when using alloca to add a random stack offset, as the Linux kernel does on syscall entry [2]. In this case, none of the alloca'd stack memory is ever used, and initializing it should be controllable; furthermore, it is not always possible to safely call memset (see [2]). Introduce `__builtin_alloca_uninitialized()` (and `__builtin_alloca_with_align_uninitialized`), which never performs initialization when `-ftrivial-auto-var-init=` is enabled. [1] https://reviews.llvm.org/D60548 [2] https://lkml.kernel.org/r/YbHTKUjEejZCLyhX@elver.google.com Reviewed By: glider Differential Revision: https://reviews.llvm.org/D115440
35 lines
1.3 KiB
C
35 lines
1.3 KiB
C
// RUN: %clang_cc1 -DSILENCE -fsyntax-only -verify -Wall %s
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// RUN: %clang_cc1 -fsyntax-only -verify -Walloca %s
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#ifdef SILENCE
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// expected-no-diagnostics
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#endif
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void test1(int a) {
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__builtin_alloca(a);
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#ifndef SILENCE
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// expected-warning@-2 {{use of function '__builtin_alloca' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
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#endif
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}
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void test2(int a) {
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__builtin_alloca_with_align(a, 32);
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#ifndef SILENCE
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// expected-warning@-2 {{use of function '__builtin_alloca_with_align' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
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#endif
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}
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void test3(int a) {
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__builtin_alloca_uninitialized(a);
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#ifndef SILENCE
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// expected-warning@-2 {{use of function '__builtin_alloca_uninitialized' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
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#endif
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}
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void test4(int a) {
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__builtin_alloca_with_align_uninitialized(a, 32);
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#ifndef SILENCE
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// expected-warning@-2 {{use of function '__builtin_alloca_with_align_uninitialized' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
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#endif
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}
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