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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Stack misaligned calling global constructor of library compiled with gcc 4.8.2"
href="https://llvm.org/bugs/show_bug.cgi?id=26779">26779</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Stack misaligned calling global constructor of library compiled with gcc 4.8.2
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.5
</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>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>f14_tomcat1@hotmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=15961" name="attach_15961" title="Crash repro">attachment 15961</a> <a href="attachment.cgi?id=15961&action=edit" title="Crash repro">[details]</a></span>
Crash repro
I have a library compiled with gcc 4.8.2 which statically initialises an array
using movaps. The movaps instruction is generated by gcc at optimization level
3.
When the library is loaded from a clang compiled application, I get a seg fault
on the movaps instruction. The pointer movaps is trying to write to is not
aligned to 16 bytes.
If I recompile the clang application with -mstackrealign, it works. It looks
like clang does not ensure the stack is aligned before calling
__global_ctx_aux.
A simple repro is attached. Here's the relevant call stack for the repro:
#0 0x00007ffff7dfc6de in _GLOBAL__sub_I_Mat4.cpp () from
./libClangCrashRepro.so
#1 0x00007ffff7dfc736 in __do_global_ctors_aux () from ./libClangCrashRepro.so
#2 0x00007ffff7dfc54b in _init () from ./libClangCrashRepro.so
#3 0x00007ffff78bb000 in ?? ()
#4 0x0000003e7260e605 in _dl_init_internal () from /lib64/ld-linux-x86-64.so.2
#5 0x0000003e72600b3a in _dl_start_user () from /lib64/ld-linux-x86-64.so.2
#6 0x0000000000000001 in ?? ()
#7 0x00007fffffffca93 in ?? ()
#8 0x0000000000000000 in ?? ()
Dump of assembler code for function _GLOBAL__sub_I_Mat4.cpp:
0x00007ffff7dfc6c0 <+0>: mov 0x200319(%rip),%rax #
0x7ffff7ffc9e0
0x00007ffff7dfc6c7 <+7>: cmpb $0x0,(%rax)
0x00007ffff7dfc6ca <+10>: jne 0x7ffff7dfc702
<_GLOBAL__sub_I_Mat4.cpp+66>
0x00007ffff7dfc6cc <+12>: movb $0x1,(%rax)
0x00007ffff7dfc6cf <+15>: mov 0x20033a(%rip),%rax #
0x7ffff7ffca10
0x00007ffff7dfc6d6 <+22>: movss 0x82(%rip),%xmm0 # 0x7ffff7dfc760
=> 0x00007ffff7dfc6de <+30>: movaps %xmm0,(%rax)
0x00007ffff7dfc6e1 <+33>: movaps 0x88(%rip),%xmm0 # 0x7ffff7dfc770
0x00007ffff7dfc6e8 <+40>: movaps %xmm0,0x10(%rax)
0x00007ffff7dfc6ec <+44>: movaps 0x8d(%rip),%xmm0 # 0x7ffff7dfc780
0x00007ffff7dfc6f3 <+51>: movaps %xmm0,0x20(%rax)
0x00007ffff7dfc6f7 <+55>: movaps 0x92(%rip),%xmm0 # 0x7ffff7dfc790
0x00007ffff7dfc6fe <+62>: movaps %xmm0,0x30(%rax)
0x00007ffff7dfc702 <+66>: repz retq
The highlighted movaps line corresponds to Mat4.h:13. The value of xmm0 is
{1,0,0,0} as expected, and rax is 6294696 which is not on a 16 byte boundary.</pre>
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