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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 - lld --exclude-libs doesn't hide builtins when using LTO"
href="https://bugs.llvm.org/show_bug.cgi?id=48681">48681</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>lld --exclude-libs doesn't hide builtins when using LTO
</td>
</tr>
<tr>
<th>Product</th>
<td>lld
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</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>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>rprichard@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, smithp352@googlemail.com
</td>
</tr></table>
<p>
<div>
<pre>Android uses --exclude-libs to hide symbols from the builtins and unwinder
libraries (e.g. libclang_rt.builtins-aarch64-android.a,
libgcc{,_real,_stripped}.a, libunwind_llvm.a, etc). When a symbol in one of
these excluded libraries isn't referenced by any LLVM IR input file, but is
referenced after the link-time compile step, then --exclude-libs fails to hide
the symbol.
Test script:
#!/bin/bash
set -e
LLVM=/x/llvm-upstream/stage1/bin
CC="$LLVM/clang -target x86_64-linux-gnu"
AR="$LLVM/llvm-ar"
cat >archive_func.c <<EOF
void __divti3() {}
EOF
cat >dso_func.c <<EOF
__int128 dso_func(__int128 x, __int128 y) { return x / y; }
EOF
$CC archive_func.c -fpic -c
rm -fr libarchive.a
$AR rcs libarchive.a archive_func.o
$CC -flto -c dso_func.c -fpic
$CC -flto -fuse-ld=lld -nostdlib dso_func.o -shared -o libdso.so
$PWD/libarchive.a -Wl,--exclude-libs,libarchive.a -Wl,-y,__divti3
$LLVM/llvm-readelf --dyn-syms -W libdso.so
Output:
$ ./test.sh
/x/mess/libarchive.a: lazy definition of __divti3
lto.tmp: reference to __divti3
/x/mess/libarchive.a(archive_func.o): definition of __divti3
Symbol table '.dynsym' contains 3 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000001370 6 FUNC GLOBAL DEFAULT 8 __divti3
2: 0000000000001380 99 FUNC GLOBAL DEFAULT 8 dso_func
I expected __divti3 to be hidden (and not appear in the `llvm-readelf
--dyn-syms` output). Removing the -flto argument when compiling dso_func.c (or
adding it when compiling archive_func.c) results in the expected output.
Both the Android platform and the NDK use --exclude-libs on builtins, but I'm
working on patches to instead mark the symbols in the archives hidden
(<a href="https://reviews.llvm.org/D93003">https://reviews.llvm.org/D93003</a> and <a href="https://reviews.llvm.org/D93431">https://reviews.llvm.org/D93431</a>). I
noticed this bug while checking to see if I had unintentionally changed
anything in the platform build.</pre>
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