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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - CodeGen doesn't respect stack alignment skew for calls (hhvm call conv.)"
href="https://bugs.llvm.org/show_bug.cgi?id=45275">45275</a>
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<th>Summary</th>
<td>CodeGen doesn't respect stack alignment skew for calls (hhvm call conv.)
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<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>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Common Code Generator Code
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>engelke@in.tum.de
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>When calling a function with the HHVM calling convention, the stack pointer
skewing of 8 bytes is not respected. hhvmcc (on x86-64) has a stack pointer
alignment of 16 bytes, which is skewed by 8 bytes, so that on entry the stack
pointer has a value of 0x...0 (instead of the usual 0x...8 with cdecl). This
skewing is ignored when generating code for a call to a hhvmcc function, making
it impossible to correctly call hhvmcc functions from LLVM.
Example:
declare hhvmcc i64 @callee(i64)
define hhvmcc i64 @caller(i64 %arg) {
%res = notail call hhvmcc i64 @callee(i64 %arg)
ret i64 %res
}
Yields:
caller:
call callee // <-- stack will be mis-aligned
ret
Note that in this example "correct" code is generated when using a tail call.
PS: I'd also be willing to take a look at this myself, but I need some pointers
where to start...</pre>
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</p>
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