Ah, it's our struct XSAVE friend again. Yeah, I think I have a pretty
good idea of what this is doing, and I believe we don't need any special
alignment there, so I just went ahead and removed it. Assuming this
doesn't cause any issues, you should be able to revert this patch.
On 13/02/2019 18:46, Jonas Devlieghere wrote:
Hi Pavel,
I think the offending struct is XSAVE in RegisterContext_x86.h. I don't
really know this code, would you mind having a look? It looks like you
touched the alignment in the past and seems to know what this this is
doing :-)
tree f8fc1af1c62b728260b6c950649c55f7aba513f6
parent 6857692687979d934e188d117eadc93f48d52a0c
author Pavel Labath <pa...@labath.sk <mailto:pa...@labath.sk>> Wed Sep
12 08:50:08 2018 +0000
committer Pavel Labath <pa...@labath.sk <mailto:pa...@labath.sk>> Wed
Sep 12 08:50:08 2018 +0000
Reduce alignment on struct XSAVE, fixing a gcc warning
The warning is about heap-allocating a struct with bigger alignment
requirements than the standard heap allocator provides.
AFAICT, all uses of the XSAVE struct are already heap-allocated, so this
high alignment does not actually have any effect and removing it should
be NFC.
I have also done some digging in the commit history. This alignment
requirement was since the XSAVE struct was introduced in r180572 when
adding AVX register support for linux. It does not mention the alignment
specifically, so I am guessing this was just put there because the
corresponging XSAVE cpu instruction requires its buffer to be 64-byte
aligned. However, LLDB will not be normally reading this struct via the
XSAVE instruction directly. Instead we will ask the kernel to copy the
buffer saved when suspeding the inferior. This should not require such
strict alignment (in fact, linux kernel will happily do this for any
alignment).
llvm-svn: 342029
On Mon, Feb 11, 2019 at 10:55 PM Pavel Labath <pa...@labath.sk
<mailto:pa...@labath.sk>> wrote:
On 12/02/2019 01:30, Jonas Devlieghere via lldb-commits wrote:
> Author: jdevlieghere
> Date: Mon Feb 11 16:30:21 2019
> New Revision: 353778
>
> URL: http://llvm.org/viewvc/llvm-project?rev=353778&view=rev
> Log:
> Define _ENABLE_EXTENDED_ALIGNED_STORAGE on Windows.
>
> Apparently there are multiple places where MSVC complains about
> instantiations with extended aligment. I think it's better to define
> `_ENABLE_EXTENDED_ALIGNED_STORAGE` as suggested by the error message.
>
> I don't have access to a Windows machine so this is all speculative.
>
I think it would be worth investigating where is this large alignment
coming from (my guess: something inside the RegisterContextDarwin
structs). We've had a case in the past where we were heap-allocating a
struct with a 64-byte alignment. MSVC would give a warning there, but
gcc&clang would silently under-align the result.
In that case, the large alignment was actually unneeded, so I fixed
both
issues by just lowering it. I suspect something similar may be possible
here.
pl
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