71 lines
3.1 KiB
Diff
71 lines
3.1 KiB
Diff
From 3d274856e792a361336eb4ae1670bc9c1905f0cb Mon Sep 17 00:00:00 2001
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From: Steinar H. Gunderson <sesse@chromium.org>
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Date: Thu, 12 May 2022 16:42:40 +0200
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Subject: [PATCH] Make AhoCorasickNode 4-aligned.
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This should fix an issue where std::vector could allocate unaligned
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memory for AhoCorasickNode, and we'd then return a pointer to
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inline_edges, where a caller would expect the pointer to be aligned
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but it wasn't.
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Change-Id: Id9dff044c61f8e46062c63b8480b18ebc68c4862
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---
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diff --git a/base/substring_set_matcher/substring_set_matcher.cc b/base/substring_set_matcher/substring_set_matcher.cc
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index e110047..ef0b750 100644
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--- a/base/substring_set_matcher/substring_set_matcher.cc
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+++ b/base/substring_set_matcher/substring_set_matcher.cc
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@@ -424,7 +424,12 @@
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edges_.inline_edges[num_edges()] = AhoCorasickEdge{label, node};
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if (label == kFailureNodeLabel) {
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// Make sure that kFailureNodeLabel is first.
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- std::swap(edges_.inline_edges[0], edges_.inline_edges[num_edges()]);
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+ // NOTE: We don't use std::swap here, because GCC
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+ // doesn't understand that inline_edges[] is 4-aligned
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+ // and gives a warning.
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+ AhoCorasickEdge temp = edges_.inline_edges[0];
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+ edges_.inline_edges[0] = edges_.inline_edges[num_edges()];
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+ edges_.inline_edges[num_edges()] = temp;
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}
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--num_free_edges_;
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return;
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diff --git a/base/substring_set_matcher/substring_set_matcher.cc b/base/substring_set_matcher/substring_set_matcher.cc
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index e110047..ef0b750 100644
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--- a/base/substring_set_matcher/substring_set_matcher.h
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+++ b/base/substring_set_matcher/substring_set_matcher.h
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@@ -154,8 +154,9 @@
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static constexpr uint32_t kEmptyLabel = 0x103;
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// A node in the trie, packed tightly together so that it occupies 12 bytes
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- // (both on 32- and 64-bit platforms).
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- class AhoCorasickNode {
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+ // (both on 32- and 64-bit platforms), but aligned to at least 4 (see the
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+ // comment on edges_).
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+ class alignas(AhoCorasickEdge) AhoCorasickNode {
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public:
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AhoCorasickNode();
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~AhoCorasickNode();
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@@ -178,6 +179,10 @@
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NodeID GetEdgeNoInline(uint32_t label) const;
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void SetEdge(uint32_t label, NodeID node);
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const AhoCorasickEdge* edges() const {
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+ // NOTE: Returning edges_.inline_edges here is fine, because it's
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+ // the first thing in the struct (see the comment on edges_).
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+ DCHECK_EQ(0u, reinterpret_cast<uintptr_t>(edges_.inline_edges) %
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+ alignof(AhoCorasickEdge));
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return edges_capacity_ == 0 ? edges_.inline_edges : edges_.edges;
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}
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@@ -258,6 +263,11 @@
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// in the first slot if it exists (ie., is not equal to kRootID), since we
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// need to access that label during every single node we look at during
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// traversal.
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+ //
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+ // NOTE: Keep this the first member in the struct, so that inline_edges gets
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+ // 4-aligned (since the class is marked as such, despite being packed.
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+ // Otherwise, edges() can return an unaligned pointer marked as aligned
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+ // (the unalignedness gets lost).
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static constexpr int kNumInlineEdges = 2;
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union {
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// Out-of-line edge storage, having room for edges_capacity_ elements.
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