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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Wrapping broken for symbols generated by LTO"
href="https://bugs.llvm.org/show_bug.cgi?id=51333">51333</a>
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<th>Summary</th>
<td>Wrapping broken for symbols generated by LTO
</td>
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<th>Product</th>
<td>lld
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>ELF
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>smeenai@fb.com
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<th>CC</th>
<td>i@maskray.me, llvm-bugs@lists.llvm.org, nathan@lanza.io, smithp352@googlemail.com
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<div>
<pre>unwind.s:
.globl _Unwind_Resume
.globl __wrap__Unwind_Resume
_Unwind_Resume:
__wrap__Unwind_Resume:
retq
$ llvm-mc -triple x86_64-linux-gnu -filetype=obj -o unwind.o unwind.s
$ ld.lld -shared -o libunwind.so unwind.o
resume.ll:
target datalayout =
"e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define dso_local void @_Z1fv() optnone noinline personality i8* bitcast (void
()* @throw to i8*) {
invoke void @throw()
to label %unreachable unwind label %lpad
lpad:
%1 = landingpad { i8*, i32 }
cleanup
resume { i8*, i32 } %1
unreachable:
unreachable
}
declare void @throw()
$ llvm-as -o resume.bc resume.ll
$ ld.lld -shared -o libresume.so resume.bc libunwind.so --gc-sections --wrap
_Unwind_Resume
Before
<a href="https://github.com/llvm/llvm-project/commit/f96ff3c0f8ebd941b3f6b345164c3d858b781484">https://github.com/llvm/llvm-project/commit/f96ff3c0f8ebd941b3f6b345164c3d858b781484</a>,
__wrap__Unwind_Resume is present in the dynamic symbol table for libunwind.so
(as shown by running `nm -D libunwind.so`), as expected. After that commit,
it's no longer present in the dynamic symbol table, and we have an invalid PLT
entry instead.
`_Unwind_Resume` isn't present in the bitcode file's symbol table, since the
reference to it is only synthesized during LTO codegen, so I imagine the symbol
is considered unreferenced and the wrapper is incorrectly dead-stripped.
Linking against the DSO defining both `_Unwind_Resume` and
`__wrap__Unwind_Resume` was necessary for the wrapping to work correctly even
before that change, so there's possibly deeper underlying issues. We always
happen to link against such a DSO though, so this was working for us prior to
f96ff3c0f8eb.
Adding `-u _Unwind_Resume` works around the issue but is inelegant.</pre>
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