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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - CFI: unclear behavior discrepancy with -O0 vs -Os when libstdc++ is linked statically"
href="https://llvm.org/bugs/show_bug.cgi?id=31775">31775</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>CFI: unclear behavior discrepancy with -O0 vs -Os when libstdc++ is linked statically
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</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>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>krasin@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=17900" name="attach_17900" title="main.cc">attachment 17900</a> <a href="attachment.cgi?id=17900&action=edit" title="main.cc">[details]</a></span>
main.cc
Consider the following c++ program:
$ cat main.cc
#include <iostream>
int main(int argc, const char *argv[]) {
std::cout << "Hello" << std::endl;
}
And the following build script:
$ cat build.sh
#!/bin/bash
set -ue
export CFLAGS="-g -c -flto -fsanitize=cfi -fsanitize-cfi-cross-dso
-fno-sanitize-trap=all -fvisibility=default"
export LDFLAGS="-flto -fuse-ld=gold -fno-sanitize-trap=all -flto -fuse-ld=gold
-fsanitize=cfi -fsanitize-cfi-cross-dso -fvisibility=default -static-libstdc++"
clang++ -O0 -o main_0.o main.cc ${CFLAGS}
clang++ -o main_0 main_0.o ${LDFLAGS}
echo "Running a binary built with -O0:"
./main_0
clang++ -Os -o main_s.o main.cc ${CFLAGS}
clang++ -o main_s main_s.o ${LDFLAGS}
echo "Running a binary built with -Os:"
./main_s
When running the script it outputs:
$ ./build.sh
Running a binary built with -O0:
Hello
Running a binary built with -Os:
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/ostream:113:9:
runtime error: control flow integrity check for type 'std::basic_ostream<char>
&(std::basic_ostream<char> &)' failed during indirect function call
(/usr/local/google/home/krasin/play/cfi-inline/main_s+0x71b70): note:
std::basic_ostream<char, std::char_traits<char> >& std::endl<char,
std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)
defined here
SUMMARY: CFI: undefined-behavior
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/ostream:113:9 in
There are few unclear moments in the report:
1. Why is it only happening at -Os, but not -O0. The answer is likely related
to inlining, but the exact cause is still not found.
2. Why isn't the address symbolized (main_s+0x71b70) and what does it point to?
3. Given that the main linkage unit has CFI and non-CFI together, it's an
unsupported combination. Do we want to do anything in order to support it? It
has been the reason for a major loss of productivity for a user.</pre>
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