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<body><span class="vcard"><a class="email" href="mailto:rnk@google.com" title="Reid Kleckner <rnk@google.com>"> <span class="fn">Reid Kleckner</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [WinEH] x64 UnwindHelp offset is wrong for realigned stack frames"
href="https://llvm.org/bugs/show_bug.cgi?id=25514">bug 25514</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
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<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>FIXED
</td>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [WinEH] x64 UnwindHelp offset is wrong for realigned stack frames"
href="https://llvm.org/bugs/show_bug.cgi?id=25514#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [WinEH] x64 UnwindHelp offset is wrong for realigned stack frames"
href="https://llvm.org/bugs/show_bug.cgi?id=25514">bug 25514</a>
from <span class="vcard"><a class="email" href="mailto:rnk@google.com" title="Reid Kleckner <rnk@google.com>"> <span class="fn">Reid Kleckner</span></a>
</span></b>
<pre>I fixed this for C++ EH with r253059.
LLVM classifies an alloca as static if it has a constant size and is in the
entry block, so your highly aligned dynamic allocas could become static through
normal optimization.
Anyway, I think fixing the CLR side of things is going to require a different
approach from UnwindHelp. I used a fixed offset stack object which is very far
from SP-after-prologue. The CLR eventually wants to use a stack offset that is
very near SP-after-prologue, so that it can minimize the size of funclet
frames.
The problem is that our realignment prologue looks like this:
SUB RSP, NN
.seh_endprologue <-- SP after prologue is set here
AND RSP, -Alignment
# Address locals from RSP offset zero
So, storing something to SP-after-prologue is very likely to conflict with
local variables, which are allocated starting from SP-after-alignment.
Changing LLVM to not use .seh_setframe would help solve this problem. If we had
a prologue like this we could easily allocate an extra slot after the aligned
local variables:
SUB RSP, LocalSize+Alignment
LEA RBP, [LocalSize+RSP]
AND RBP, Alignment
.seh_endprologue</pre>
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