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From 94ffefa81d00466fabcf1050080c95fa4b294dda Mon Sep 17 00:00:00 2001
From: Elly Fong-Jones <ellyjones@chromium.org>
Date: Thu, 2 Mar 2023 00:15:11 +0000
Subject: [PATCH 1/9] sql: relax constraints on VirtualCursor layout
VirtualCursor::FromSqliteCursor required that VirtualCursor had a
standard layout, but in fact VirtualCursor shouldn't have a standard
layout, and the fact that it does with libc++ is a deviation from the
C++ standard. This change:
1. Relaxes the requirement that VirtualCursor has a standard layout, and
2. Relaxes the requirement that the sqlite_cursor_ field has to be at
offset 0
by use of offsetof() and pointer subtraction. This change both improves
standards compliance and makes this code build with libstdc++.
Bug: 1380656
Change-Id: I9c47abd9197b187da0360ca5619ccf7dadab4f33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4292313
Reviewed-by: Austin Sullivan <asully@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1111925}
---
sql/recover_module/cursor.h | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/sql/recover_module/cursor.h b/sql/recover_module/cursor.h
index 1970bdca8c6f1..4cb0655700977 100644
--- a/sql/recover_module/cursor.h
+++ b/sql/recover_module/cursor.h
@@ -63,12 +63,10 @@ class VirtualCursor {
// |sqlite_cursor| must have been returned by VirtualTable::SqliteCursor().
static inline VirtualCursor* FromSqliteCursor(
sqlite3_vtab_cursor* sqlite_cursor) {
- static_assert(std::is_standard_layout<VirtualCursor>::value,
- "needed for the reinterpret_cast below");
- static_assert(offsetof(VirtualCursor, sqlite_cursor_) == 0,
- "sqlite_cursor_ must be the first member of the class");
- VirtualCursor* result = reinterpret_cast<VirtualCursor*>(sqlite_cursor);
- DCHECK_EQ(sqlite_cursor, &result->sqlite_cursor_);
+ VirtualCursor* result = reinterpret_cast<VirtualCursor*>(
+ (reinterpret_cast<char*>(sqlite_cursor) -
+ offsetof(VirtualCursor, sqlite_cursor_)));
+ CHECK_EQ(sqlite_cursor, &result->sqlite_cursor_);
return result;
}
--
2.39.2
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