EricWF created this revision.
EricWF added reviewers: mclow.lists, danalbert, jroelofs, compnerd.
EricWF added a subscriber: cfe-commits.
In 32 bit builds on a 64 bit system `std::malloc` does not return correctly
aligned memory. This leads to undefined behavior.
This patch switches to using `posix_memalign` to allocate correctly aligned
memory instead.
https://reviews.llvm.org/D25417
Files:
src/cxa_exception.cpp
src/fallback_malloc.cpp
test/test_exception_address_alignment.pass.cpp
Index: test/test_exception_address_alignment.pass.cpp
===================================================================
--- /dev/null
+++ test/test_exception_address_alignment.pass.cpp
@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// Test that the address of the exception object is properly aligned to the
+// largest supported alignment for the system.
+
+#include <cstdint>
+#include <cassert>
+
+struct __attribute__((aligned)) AlignedType {};
+struct MinAligned { };
+static_assert(alignof(MinAligned) == 1 && sizeof(MinAligned) == 1, "");
+
+int main() {
+ for (int i=0; i < 10; ++i) {
+ try {
+ throw MinAligned{};
+ } catch (MinAligned const& ref) {
+ assert(reinterpret_cast<uintptr_t>(&ref) % alignof(AlignedType) == 0);
+ }
+ }
+}
Index: src/fallback_malloc.cpp
===================================================================
--- src/fallback_malloc.cpp
+++ src/fallback_malloc.cpp
@@ -196,11 +196,13 @@
#pragma GCC visibility push(hidden)
+struct __attribute__((aligned)) __aligned_type {};
+
void * __malloc_with_fallback(size_t size) {
- void *ptr = std::malloc(size);
- if (NULL == ptr) // if malloc fails, fall back to emergency stash
- ptr = fallback_malloc(size);
- return ptr;
+ void* dest;
+ if (::posix_memalign(&dest, alignof(__aligned_type), size) == 0)
+ return dest;
+ return fallback_malloc(size);
}
void * __calloc_with_fallback(size_t count, size_t size) {
Index: src/cxa_exception.cpp
===================================================================
--- src/cxa_exception.cpp
+++ src/cxa_exception.cpp
@@ -65,12 +65,16 @@
return cxa_exception_from_thrown_object(unwind_exception + 1 );
}
-static
-inline
-size_t
-cxa_exception_size_from_exception_thrown_size(size_t size)
-{
- return size + sizeof (__cxa_exception);
+// Round s up to next multiple of a.
+static inline
+size_t aligned_allocation_size(size_t s, size_t a) {
+ return (s + a - 1) & ~(a - 1);
+}
+
+static inline
+size_t cxa_exception_size_from_exception_thrown_size(size_t size) {
+ return aligned_allocation_size(size + sizeof (__cxa_exception),
+ alignof(__cxa_exception));
}
static void setExceptionClass(_Unwind_Exception* unwind_exception) {
Index: test/test_exception_address_alignment.pass.cpp
===================================================================
--- /dev/null
+++ test/test_exception_address_alignment.pass.cpp
@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// Test that the address of the exception object is properly aligned to the
+// largest supported alignment for the system.
+
+#include <cstdint>
+#include <cassert>
+
+struct __attribute__((aligned)) AlignedType {};
+struct MinAligned { };
+static_assert(alignof(MinAligned) == 1 && sizeof(MinAligned) == 1, "");
+
+int main() {
+ for (int i=0; i < 10; ++i) {
+ try {
+ throw MinAligned{};
+ } catch (MinAligned const& ref) {
+ assert(reinterpret_cast<uintptr_t>(&ref) % alignof(AlignedType) == 0);
+ }
+ }
+}
Index: src/fallback_malloc.cpp
===================================================================
--- src/fallback_malloc.cpp
+++ src/fallback_malloc.cpp
@@ -196,11 +196,13 @@
#pragma GCC visibility push(hidden)
+struct __attribute__((aligned)) __aligned_type {};
+
void * __malloc_with_fallback(size_t size) {
- void *ptr = std::malloc(size);
- if (NULL == ptr) // if malloc fails, fall back to emergency stash
- ptr = fallback_malloc(size);
- return ptr;
+ void* dest;
+ if (::posix_memalign(&dest, alignof(__aligned_type), size) == 0)
+ return dest;
+ return fallback_malloc(size);
}
void * __calloc_with_fallback(size_t count, size_t size) {
Index: src/cxa_exception.cpp
===================================================================
--- src/cxa_exception.cpp
+++ src/cxa_exception.cpp
@@ -65,12 +65,16 @@
return cxa_exception_from_thrown_object(unwind_exception + 1 );
}
-static
-inline
-size_t
-cxa_exception_size_from_exception_thrown_size(size_t size)
-{
- return size + sizeof (__cxa_exception);
+// Round s up to next multiple of a.
+static inline
+size_t aligned_allocation_size(size_t s, size_t a) {
+ return (s + a - 1) & ~(a - 1);
+}
+
+static inline
+size_t cxa_exception_size_from_exception_thrown_size(size_t size) {
+ return aligned_allocation_size(size + sizeof (__cxa_exception),
+ alignof(__cxa_exception));
}
static void setExceptionClass(_Unwind_Exception* unwind_exception) {
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