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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 - rodata size bloat with file names when using -fsanitize=function with -fsanitize=address"
href="https://bugs.llvm.org/show_bug.cgi?id=39347">39347</a>
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<th>Summary</th>
<td>rodata size bloat with file names when using -fsanitize=function with -fsanitize=address
</td>
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<th>Product</th>
<td>clang
</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>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>sugak@fb.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>I noticed a significant bloat of .rodata section when using both
-fsanitize=function and -fsanitize=address. Inspecting the section showed that
it's significant part are strings with file names.
I tried to use `-fsanitize-undefined-strip-path-components=-1`, but it happens
to not work with this ubsan check, and the full string names still make it into
the binary.
The repro:
```
# verify file name is not in the rodata
% cat main.cpp
int main() {return 0;}
% clang++ -fsanitize=function $(realpath main.cpp)
% readelf -p .rodata a.out | grep main.cpp
[Exit 1] # no match
# now enable ASAN
% clang++ -fsanitize=function -fsanitize=address $(realpath main.cpp)
% readelf -p .rodata a.out | grep main.cpp
[ 17680] /very/long/path/main.cpp
# now use -fsanitize-undefined-strip-path-components=-1
% clang++ -fsanitize=function -fsanitize=address
-fsanitize-undefined-strip-path-components=-1 $(realpath main.cpp)
% readelf -p .rodata a.out | grep main.cpp
[ 17680] /very/long/path/main.cpp # it didn't help
```
I've also verified that the file name is not emitted to rodata when only ASAN
is used. And `-fsanitize-undefined-strip-path-components=-1` works for the
other UBSAN checks that I've used.
I was able to narrow the problem down to this block
<a href="https://github.com/llvm-mirror/clang/blob/ebb3b3ca30bc377eeebfac5e56b940f9a22b5b64/lib/CodeGen/CGExpr.cpp#L4616">https://github.com/llvm-mirror/clang/blob/ebb3b3ca30bc377eeebfac5e56b940f9a22b5b64/lib/CodeGen/CGExpr.cpp#L4616</a>
Looks like -fsanize=function emits a global variable with a file name and then
ASAN instruments it. Not sure why the filename doesn't make it to the resulting
binary when ASAN is disabled.
I don't completely understand the consequences of the above-mentioned block,
but commenting it out and then rebuilding some of our binary reduses the bloat
by ~30%!</pre>
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