From 6823f6783082faee54da823623ad4a01edcd1865 Mon Sep 17 00:00:00 2001 From: Mark Mentovai Date: Tue, 27 Jun 2017 11:13:16 -0400 Subject: [PATCH] Limit alignas to 64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Although GCC will silently accept larger alignments with __attribute__((aligned())), it warn on alignas() with an alignment larger than the target’s supported maximum. 8c35d92ae403 switched to alignas() where possible. The maxima are at least 128 on x86, x86_64, and arm64, and 64 on arm, in the common configurations, but may be even larger with certain features such as AVX enabled. These are ultimately derived from BIGGEST_ALIGNMENT in gcc/config/*/*.h. One alignment request in a test specified 1024 as a big alignment constraint, solely as a test that alignment worked correctly. For this, it’s perfectly reasonable to limit the alignment request to what GCC supports on the most constrained target we’ll encounter. Test: crashapd_util_test AlignedAllocator.AlignedVector Change-Id: I42af443f437e01228934ab34dc04983742f0ab3f Reviewed-on: https://chromium-review.googlesource.com/550236 Reviewed-by: Scott Graham Commit-Queue: Mark Mentovai --- util/stdlib/aligned_allocator_test.cc | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/util/stdlib/aligned_allocator_test.cc b/util/stdlib/aligned_allocator_test.cc index 4a018f58..d52dcfa2 100644 --- a/util/stdlib/aligned_allocator_test.cc +++ b/util/stdlib/aligned_allocator_test.cc @@ -52,10 +52,10 @@ TEST(AlignedAllocator, AlignedVector) { IsAligned(&natural_aligned_vector[2], alignof(NaturalAlignedStruct))); // Test a structure that declares its own alignment. - struct alignas(32) AlignedStruct { + struct alignas(16) AlignedStruct { int i; }; - ASSERT_EQ(alignof(AlignedStruct), 32u); + ASSERT_EQ(alignof(AlignedStruct), 16u); AlignedVector aligned_vector; aligned_vector.push_back(AlignedStruct()); @@ -69,15 +69,15 @@ TEST(AlignedAllocator, AlignedVector) { // Try a custom alignment. Since the structure itself doesn’t specify an // alignment constraint, only the base address will be aligned to the // requested boundary. - AlignedVector custom_aligned_vector; + AlignedVector custom_aligned_vector; custom_aligned_vector.push_back(NaturalAlignedStruct()); - EXPECT_TRUE(IsAligned(&custom_aligned_vector[0], 64)); + EXPECT_TRUE(IsAligned(&custom_aligned_vector[0], 32)); // Try a structure with a pretty big alignment request. - struct alignas(1024) BigAlignedStruct { + struct alignas(64) BigAlignedStruct { int i; }; - ASSERT_EQ(alignof(BigAlignedStruct), 1024u); + ASSERT_EQ(alignof(BigAlignedStruct), 64u); AlignedVector big_aligned_vector; big_aligned_vector.push_back(BigAlignedStruct());