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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x64] Improper CFI used for function clobbering FLAGS register"
href="https://llvm.org/bugs/show_bug.cgi?id=25945">25945</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[x64] Improper CFI used for function clobbering FLAGS register
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.majnemer@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>consider:
define i64 @test_intervening_call(i64* %foo, i64 %bar, i64 %baz) {
%cx = cmpxchg i64* %foo, i64 %bar, i64 %baz seq_cst seq_cst
%v = extractvalue { i64, i1 } %cx, 0
%p = extractvalue { i64, i1 } %cx, 1
call void asm sideeffect "", "~{cc},~{dirflag},~{fpsr},~{flags}"()
br i1 %p, label %t, label %f
t:
ret i64 42
f:
ret i64 0
}
this results in:
test_intervening_call: # @test_intervening_call
.Ltmp0:
.seh_proc test_intervening_call
# BB#0:
.Ltmp1:
.seh_endprologue
movq %rdx, %rax
lock cmpxchgq %r8, (%rcx)
pushfq <---- uh, oh...
popq %rax
#APP
#NO_APP
pushq %rax
popfq
jne .LBB0_2
# BB#1: # %t
movl $42, %eax
retq
.LBB0_2: # %f
xorl %eax, %eax
retq
.seh_handlerdata
Notice how we are manipulating the stack pointer even though we don't have a
frame pointer.</pre>
</div>
</p>
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