| commit | 01f99b4e9540f34b44e13b25f6dd04b82ac952d9 | [log] [tgz] |
|---|---|---|
| author | Keith Randall <khr@golang.org> | Tue Aug 11 13:07:35 2020 -0700 |
| committer | Keith Randall <khr@golang.org> | Sun Aug 16 17:05:28 2020 +0000 |
| tree | ec18a4ca73b57a0ab1c4b2b38d5e5150422eab45 | |
| parent | c6a11f0dd279f374602794af60c7cde4585a1e6f [diff] |
cmd/compile: mark DUFFZERO/DUFFCOPY as async unsafe These operations are async unsafe on architectures that use frame pointers. The reason is they rely on data being safe when stored below the stack pointer. They do: 45da69: 48 89 6c 24 f0 mov %rbp,-0x10(%rsp) 45da6e: 48 8d 6c 24 f0 lea -0x10(%rsp),%rbp 45da73: e8 7d d0 ff ff callq 45aaf5 <runtime.duffzero+0x115> 45da78: 48 8b 6d 00 mov 0x0(%rbp),%rbp This dance ensures that inside duffzero, it looks like there is a proper frame pointer set up, so that stack walkbacks work correctly if the kernel samples during duffzero. However, this instruction sequence depends on data not being clobbered even though it is below the stack pointer. If there is an async interrupt at any of those last 3 instructions, and the interrupt decides to insert a call to asyncPreempt, then the saved frame pointer on the stack gets clobbered. The last instruction above then restores junk to the frame pointer. To prevent this, mark these instructions as async unsafe. (The body of duffzero is already async unsafe, as it is in package runtime.) Change-Id: I5562e82f9f5bd2fb543dcf2b6b9133d87ff83032 Reviewed-on: https://go-review.googlesource.com/c/go/+/248261 Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Martin Möhrmann <moehrmann@google.com> Reviewed-by: Cherry Zhang <cherryyz@google.com>
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