<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - make -fsanitize-coverage=pc-table friendly with -ffunction-sections -Wl,-gc-sections"
href="https://bugs.llvm.org/show_bug.cgi?id=34636">34636</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>make -fsanitize-coverage=pc-table friendly with -ffunction-sections -Wl,-gc-sections
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>mascasa@google.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kcc@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>ekarpenkov@apple.com, eugeni.stepanov@gmail.com, llvm-bugs@justinbogner.com, llvm-bugs@lists.llvm.org, peter@pcc.me.uk
</td>
</tr></table>
<p>
<div>
<pre>[discussed previously at
<a href="http://lists.llvm.org/pipermail/llvm-dev/2017-September/117315.html">http://lists.llvm.org/pipermail/llvm-dev/2017-September/117315.html</a>]
On linux we have two problems with -fsanitize=fuzzer and -ffunction-sections
-Wl,-gc-sections
Test for these: projects/compiler-rt/test/fuzzer/GcSectionsTest.cpp
First problem:
% clang -std=c++11 -ffunction-sections -Wl,-gc-sections -fsanitize=fuzzer
GcSectionsTest.cpp
/tmp/GcSectionsTest-065286.o: In function `sancov.module_ctor':
GcSectionsTest.cpp:(.text.sancov.module_ctor[sancov.module_ctor]+0x22):
undefined reference to `__start___sancov_pcs'
GcSectionsTest.cpp:(.text.sancov.module_ctor[sancov.module_ctor]+0x2c):
undefined reference to `__stop___sancov_pcs'
Here, the table produced by -fsanitize-coverage=pc-table __sancov_pcs gets
dropped by the bfd linker (on Ubuntu 14.04).
With a better linker (-fuse-ld=gold or -fuse-ld=lld) this doesn't happen,
but we still *may* need to find a workaround suitable for old ld. Or maybe not.
Second:
% clang -std=c++11 -ffunction-sections -Wl,-gc-sections -fsanitize=fuzzer
GcSectionsTest.cpp -fuse-ld=lld && nm a.out | grep Unused
000000000023f590 t UnusedFunctionShouldBeRemovedByLinker
here, gc-sections is essentially disabled because -fsanitize-coverage=pc-table
makes all functions used.
eugenis@ suggests that all we need here is to use
<a href="https://llvm.org/docs/LangRef.html#associated-metadata">https://llvm.org/docs/LangRef.html#associated-metadata</a> to mark the pc-table as
associated with it's function.
This is important, we need gc-sections to work.
But once we fix it, we'll need a test (in test/fuzzer/gc-sections.test)
but the test won't work with bfd linker, see above.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>