From 94ffefa81d00466fabcf1050080c95fa4b294dda Mon Sep 17 00:00:00 2001 From: Elly Fong-Jones 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 Commit-Queue: Elly Fong-Jones 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::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(sqlite_cursor); - DCHECK_EQ(sqlite_cursor, &result->sqlite_cursor_); + VirtualCursor* result = reinterpret_cast( + (reinterpret_cast(sqlite_cursor) - + offsetof(VirtualCursor, sqlite_cursor_))); + CHECK_EQ(sqlite_cursor, &result->sqlite_cursor_); return result; } -- 2.39.2