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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 - Bad interaction with llvm-objcopy + gold"
href="https://bugs.llvm.org/show_bug.cgi?id=42052">42052</a>
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<th>Summary</th>
<td>Bad interaction with llvm-objcopy + gold
</td>
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<th>Product</th>
<td>tools
</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>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>llvm-objcopy/strip
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>rupprecht@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>alexander.v.shaposhnikov@gmail.com, jake.h.ehrlich@gmail.com, jh7370.2008@my.bristol.ac.uk, llvm-bugs@lists.llvm.org, rupprecht@google.com
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<p>
<div>
<pre>Before llvm-objcopy writes out, it sorts sections by offset:
<a href="https://github.com/llvm/llvm-project/blob/master/llvm/tools/llvm-objcopy/ELF/Object.cpp#L1480">https://github.com/llvm/llvm-project/blob/master/llvm/tools/llvm-objcopy/ELF/Object.cpp#L1480</a>
However, gold expects that the index of section groups is smaller than the
indices of sections that it contains:
<a href="https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gold/object.cc;h=689448f50c8a784d1142032875203ffc1d28661f;hb=HEAD#l1090">https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gold/object.cc;h=689448f50c8a784d1142032875203ffc1d28661f;hb=HEAD#l1090</a>
This does seem to be required by the ELF spec: "The section header table entry
for a group section must appear in the section header table before the entries
for any of the sections that are members of the group." Only gold complains
though -- ld and lld work fine (accepting invalid ELF, I guess).
Because llvm-objcopy only looks at the offsets, if an SHT_GROUP section has a
greater offset than the sections it contains (while still having the section
header come first), llvm-objcopy can rearrange it into an invalid ordering.
Small-ish repro:
$ cat repro.cc
#include <string>
std::string foo(std::string x) { return x + x; }
int main() {
foo("x");
return 0;
}
# Normal link w/ gold (passes)
$ clang++ -c group.cc -o /tmp/group.o
$ clang++ -fuse-ld=gold -o /tmp/group /tmp/group.o
# Invoke GNU objcopy & link w/ gold (passes)
$ objcopy /tmp/group.o /tmp/group.gnu.o
$ clang++ -fuse-ld=gold -o /tmp/group /tmp/group.gnu.o
# Invoke llvm-objcopy & link w/ gold (fails)
$ llvm-objcopy /tmp/group.o /tmp/group.llvm.o
$ clang++ -fuse-ld=gold -o /tmp/group /tmp/group.llvm.o
/usr/bin/ld.gold: error: /tmp/group.llvm.o: invalid section group 8 refers to
earlier section 2
The simplest thing is probably to change that comparator to always put
SHT_GROUP first, which I believe is effectively what GNU objcopy does.</pre>
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