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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Invalid prolog/epilog on Win64"
href="http://llvm.org/bugs/show_bug.cgi?id=16779">16779</a>
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</tr>
<tr>
<th>Summary</th>
<td>Invalid prolog/epilog on Win64
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nico.rieck@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The "Prolog and Epilog" section
<<a href="http://msdn.microsoft.com/en-us/library/tawsa7cb.aspx">http://msdn.microsoft.com/en-us/library/tawsa7cb.aspx</a>> of Microsofts x64
conventions state:
"These are the only legal forms for an epilog. It must consist of either an
add RSP,constant or lea RSP,constant[FPReg], followed by a series of zero or
more 8-byte register pops and a return or a jmp. [...]"
But LLVM uses mov to restore RSP. Also, if a stack variable has an alignment
greater than 16, RSP is realigned during the prolog which is incompatible with
x64 unwind information.
Example:
// clang -std=c++11 -m64 -target x86_64-pc-win32 -o -
int foo()
{
alignas(32) int x = 0;
return x;
}
Produces:
.def _Z3foov;
.scl 2;
.type 32;
.endef
.text
.globl _Z3foov
.align 16, 0x90
_Z3foov:
pushq %rbp
movq %rsp, %rbp
andq $-32, %rsp // realignment before rsp is adjusted
subq $32, %rsp
movl $0, (%rsp)
xorl %eax, %eax
movq %rbp, %rsp // mov in epilog
popq %rbp
ret</pre>
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