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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [PPC] Lowering of llvm.init_trampoline problem with libgcc"
href="https://bugs.llvm.org/show_bug.cgi?id=49004">49004</a>
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<th>Summary</th>
<td>[PPC] Lowering of llvm.init_trampoline problem with libgcc
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: PowerPC
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>v.churavy@gmail.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nemanja.i.ibm@gmail.com
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<p>
<div>
<pre>@llvm.init_trampoline on PPC lowers [1] to a call to `__trampoline_setup` which
IIUC is either defined in libgcc [2] or compiler-rt [3]. As far as I can tell
`compiler-rt` doesn't implement it for powerpc64le, and libgcc has a bug in the
assembly where it checks that the passed `trampoline size` (size of the
allocated buffer) is **smaller** than the required/computed by the linker
`trampoline size`. `r8` contains the trampoline size as calculated by the
linker, and `r4` contains the trampoline size passed in from the outside. LLVM
will always pass 48 as a value on ppc64le, whereas the calculated trampoline
size could vary and on the systems I have access to is `32`.
`libgcc` then does a:
if (r4 < r8)
abort();
[1]
<a href="https://github.com/llvm/llvm-project/blob/ffc3e800c65ee58166255ff897f8b7e6d850ddda/llvm/lib/Target/PowerPC/PPCISelLowering.cpp#L3485">https://github.com/llvm/llvm-project/blob/ffc3e800c65ee58166255ff897f8b7e6d850ddda/llvm/lib/Target/PowerPC/PPCISelLowering.cpp#L3485</a>
[2]
<a href="https://github.com/gcc-mirror/gcc/blob/02551aa99960ff6b0d9a44d234b8f6c9b230788c/libgcc/config/rs6000/tramp.S#L150">https://github.com/gcc-mirror/gcc/blob/02551aa99960ff6b0d9a44d234b8f6c9b230788c/libgcc/config/rs6000/tramp.S#L150</a>
[3]
<a href="https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/builtins/trampoline_setup.c">https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/builtins/trampoline_setup.c</a>
I haven't been able to fill a bug against libgcc since account registration is
restricted.</pre>
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