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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Miscompilation of va_start on Windows MSYS2"
href="https://bugs.llvm.org/show_bug.cgi?id=48624">48624</a>
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<th>Summary</th>
<td>Miscompilation of va_start on Windows MSYS2
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>release blocker
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>husseydevin@gmail.com
</td>
</tr>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Not sure if this is a Clang bug or a MSYS2 bug, so I am filing it here.
However, since the problem doesn't affect GCC which links to the same libc, I
am assuming it is something fishy with clang.
Compile this rather simple C program on MSYS2:
#include <stdarg.h>
#include <stdio.h>
void my_printf(const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vprintf(fmt, ap);
va_end(ap);
}
int main(void)
{
my_printf("%s\n", "Hello, world!");
}
***@**** MSYS2 ~
$ clang --version
clang version 11.0.0 (<a href="https://github.com/msys2/MSYS2-packages">https://github.com/msys2/MSYS2-packages</a>
a5a028a0811f03c8f9697bf80c2e28111628ffff)
Target: x86_64-pc-windows-msys
Thread model: posix
InstalledDir: /usr/bin
***@**** MSYS2 ~
$ clang test.c; ./a.exe
0@
***@**** MSYS2 ~
$./a.exe | hexdump -C
00000000 04 30 40 0a |.0@.|
00000004
In case you are wondering, GCC correctly compiles this; my libc isn't broken.
***@**** MSYS2 ~
$ gcc --version
gcc (GCC) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
***@**** MSYS2 ~
$ gcc test.c; ./a.exe
Hello, world!
It doesn't matter if optimizations are on or off, it still prints 0x04 0x30
0x40.
mingw-w64 clang compiles it fine, though.
Doing some more investigation now, although I am not familiar with the calling
convention.</pre>
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