<html>
<head>
<base href="http://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - variadic function with AMD64 abi and windows calling convention"
href="http://llvm.org/bugs/show_bug.cgi?id=20847">20847</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>variadic function with AMD64 abi and windows calling convention
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>maxime.madau@hp.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=12986" name="attach_12986" title="test code">attachment 12986</a> <a href="attachment.cgi?id=12986&action=edit" title="test code">[details]</a></span>
test code
Hi,
Architecture: linux x86-64.
Compilation command line : clang hello.c -o hello
expected output: 1 2 3 4 5 6 7 8 9 10
output: 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10
When using __attribute__((ms_abi)) on a variadic function with more than 6
arguments, the program will reiterate at the beginning of the argument passed
on the stack (test code attached).
Firstly, clang pushes all arguments after the first 6 arguments (creates the
register save area) in the stack before the base pointer. Then clang emits the
va_arg and va_list for System V AMD64 and thus instead of going on the stack
and accessing all arguments one-by-one like Microsoft calling convention does,
it goes through the stack until gp_offset is > 48 (e.g until the end of the
register save area, which is located before the base pointer in my program).
Finally, it reiterates starting from the beginning of the register save area.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>