From 294dc053e442aae7ee87c827dfa6f6301c492d47 Mon Sep 17 00:00:00 2001
From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Date: Tue, 19 May 2020 00:49:51 +0200
Subject: [PATCH] sql: make BtCursor's memory aligned
Vdbe at runtime allocates VdbeCursor structure using
allocateCursor() function. Inside there is a pointer at BtCursor
structure. To make the allocation faster and improve cache
locality, both cursors are allocated in one memory block + some
extra memory for uint32_t array, where BtCursor followed
VdbeCursor and the array without any padding:
VdbeCursor + uint32_t * N + BtCursor
The problem is that BtCursor needs 8 byte alignment. When it
followed VdbeCursor (aligned by 8) + some uint32_t values, its
actual alignment could become 4 bytes. That led to a crash when
alignment sanitizer is enabled in clang.
The patch makes BtCursor offset aligned by 8 bytes.
Part of #4609
---
src/box/sql/vdbe.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/src/box/sql/vdbe.c b/src/box/sql/vdbe.c
index 724bc188b3..7a42602a21 100644
--- a/src/box/sql/vdbe.c
+++ b/src/box/sql/vdbe.c
@@ -234,10 +234,9 @@ allocateCursor(
*/
Mem *pMem = iCur>0 ? &p->aMem[p->nMem-iCur] : p->aMem;
- int nByte;
VdbeCursor *pCx = 0;
- nByte =
- ROUND8(sizeof(VdbeCursor)) + sizeof(u32)*nField +
+ int bt_offset = ROUND8(sizeof(VdbeCursor) + sizeof(uint32_t) * nField);
+ int nByte = bt_offset +
(eCurType==CURTYPE_TARANTOOL ? ROUND8(sizeof(BtCursor)) : 0);
assert(iCur>=0 && iCur<p->nCursor);
@@ -251,8 +250,7 @@ allocateCursor(
pCx->eCurType = eCurType;
pCx->nField = nField;
if (eCurType==CURTYPE_TARANTOOL) {
- pCx->uc.pCursor = (BtCursor*)
- &pMem->z[ROUND8(sizeof(VdbeCursor))+sizeof(u32)*nField];
+ pCx->uc.pCursor = (BtCursor*)&pMem->z[bt_offset];
sqlCursorZero(pCx->uc.pCursor);
}
}
--
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