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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Mishandling SEH filters for available_externally functions"
href="https://bugs.llvm.org/show_bug.cgi?id=35142">35142</a>
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</tr>
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<th>Summary</th>
<td>Mishandling SEH filters for available_externally functions
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<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>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Core LLVM classes
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>peter@pcc.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>$ cat 1.cc
static void try_body(int numerator, int denominator, int *myres) {
*myres = numerator / denominator;
}
inline int safe_div(int numerator, int denominator, int *res) {
int myres = 0;
int success = 1;
__try {
try_body(numerator, denominator, &myres);
} __except (1) {
success = -42;
}
*res = myres;
return success;
}
void *f() { return (void *)&safe_div; }
$ cat 2.cc
static void try_body(int numerator, int denominator, int *myres) {
*myres = numerator / denominator;
}
inline int safe_div(int numerator, int denominator, int *res) {
int myres = 0;
int success = 1;
__try {
try_body(numerator, denominator, &myres);
} __except (1) {
success = -42;
}
*res = myres;
return success;
}
void *g() { return (void *)&safe_div; }
$ clang-cl /c 1.cc 2.cc -flto=thin -m32
$ lld-link 1.obj 2.obj /nodefaultlib /entry:f /opt:lldlto=0 /lldsavetemps
LLVM ERROR: assembler label 'L?safe_div@@YAHHHPAH@Z$parent_frame_offset' can
not be undefined
What's going on here is that the linker is choosing 1.obj's definition of
safe_div as prevailing, and requesting that 2.obj's definition be dropped. It
does this by setting linkage to available_externally. This reveals two bugs.
The first is that the localrecover check in Verifier.cpp is insufficient; under
the current semantics it would need to account for available_externally linkage
by calling isDeclarationForLinker instead of isDeclaration.
Even if we did that, though, we'd still hit a verifier check for this test
case, and the fix for that bug is unclear. At the object file level, 2.obj
contains an SEH filter with information about the non-prevailing definition of
safe_seh. The fix I have in mind is that because it is impossible for there to
be an active stack frame for said non-prevailing definition, the behaviour of
the SEH filter is undefined, and we can simply treat the intrinsic call as
equivalent to unreachable if it refers to an undefined function.</pre>
</div>
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