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8364235: Fix for JDK-8361447 breaks the alignment requirements for GuardedMemory

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Co-authored-by: Johan Sjölen <jsjolen@openjdk.org>
Reviewed-by: dcubed, jsjolen, aboldtch
This commit is contained in:
David Holmes 2025-08-07 04:37:21 +00:00
parent 7e484e2a63
commit 078d0d4968
1 changed files with 12 additions and 6 deletions
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18
src/hotspot/share/memory/guardedMemory.hpp
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@ -42,9 +42,10 @@
* |Offset | Content | Description |
* |------------------------------------------------------------
* |base_addr | 0xABABABABABABABAB | Head guard |
* |+16 | <size_t:user_size> | User data size |
* |+sizeof(uintptr_t) | <tag> | Tag word |
* |+sizeof(uintptr_t) | <tag2> | Tag word |
* |+GUARD_SIZE | <size_t:user_size> | User data size |
* |+sizeof(size_t) | <tag> | Tag word |
* |+sizeof(void*) | <tag2> | Tag word |
* |+sizeof(void*) | <pad bytes> | Padding |
* |+sizeof(void*) | 0xF1 <user_data> ( | User data |
* |+user_size | 0xABABABABABABABAB | Tail guard |
* -------------------------------------------------------------
@ -52,6 +53,8 @@
* Where:
* - guard padding uses "badResourceValue" (0xAB)
* - tag word and tag2 word are general purpose
* - padding is inserted as-needed by the compiler to ensure
* the user data is aligned on a 16-byte boundary
* - user data
* -- initially padded with "uninitBlockPad" (0xF1),
* -- to "freeBlockPad" (0xBA), when freed
@ -132,12 +135,15 @@ protected:
/**
* Header guard and size
*
* NB: the size and placement of the GuardHeader must be such that the
* user-ptr is maximally aligned i.e. 16-byte alignment for x86 ABI for
* stack alignment and use of vector (xmm) instructions. We use alignas
* to achieve this.
*/
class GuardHeader : Guard {
class alignas(16) GuardHeader : Guard {
friend class GuardedMemory;
protected:
// Take care in modifying fields here, will effect alignment
// e.g. x86 ABI 16 byte stack alignment
union {
uintptr_t __unused_full_word1;
size_t _user_size;