| commit | 5b15510d96b00662327fbd3eb860d767834dfadc | [log] [tgz] |
|---|---|---|
| author | Austin Clements <austin@google.com> | Thu Jul 18 12:30:37 2019 -0400 |
| committer | Austin Clements <austin@google.com> | Fri Jul 19 15:04:08 2019 +0000 |
| tree | 70b68e7a3112a6ea381f2fbfb406bf3b32c06949 | |
| parent | ba3149612f62c011765876d7a437095fa50e0771 [diff] |
runtime: align allocations harder in GODEBUG=sbrk=1 mode Currently, GODEBUG=sbrk=1 mode aligns allocations by their type's alignment. You would think this would be the right thing to do, but because 64-bit fields are only 4-byte aligned right now (see #599), this can cause a 64-bit field of an allocated object to be 4-byte aligned, but not 8-byte aligned. If there is an atomic access to that unaligned 64-bit field, it will crash. This doesn't happen in normal allocation mode because the size-segregated allocation and the current size classes will cause any types larger than 8 bytes to be 8 byte aligned. We fix this by making sbrk=1 mode use alignment based on the type's size rather than its declared alignment. This matches how the tiny allocator aligns allocations. This was tested with GOARCH=386 GODEBUG=sbrk=1 go test sync/atomic This crashes with an unaligned access before this change, and passes with this change. This should be reverted when/if we fix #599. Fixes #33159. Change-Id: Ifc52c72c6b99c5d370476685271baa43ad907565 Reviewed-on: https://go-review.googlesource.com/c/go/+/186919 Run-TryBot: Austin Clements <austin@google.com> Reviewed-by: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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