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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang should not generate counting function for functions with no_instrument_function attribute."
href="https://bugs.llvm.org/show_bug.cgi?id=33515">33515</a>
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<th>Summary</th>
<td>clang should not generate counting function for functions with no_instrument_function attribute.
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</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>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>manojgupta@google.com
</td>
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<th>Reporter</th>
<td>manojgupta@google.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>When -pg is used, clang generates counting functions even for functions with
no_instrument_function attribute.
This results in a Linux kernel crash when function tracing is enabled in Chrome
OS.
GCC behavior is to not generate any counting functions with
no_instrument_function attribute.
Apparently, this is also desired in clang according to the comment in
SemaDeclAttr.cpp but the implementation is broken.
llvm/tools/clang/lib/Sema/SemaDeclAttr.cpp: case
AttributeList::AT_NoInstrumentFunction: // Interacts with -pg.
$ cat pg.c
__attribute__((no_instrument_function)) void foo()
{
}
$ clang pg.c -c -pg -target aarch64-unknown-linux-gnu
$ aarch64-linux-gnu-objdump -d pg.o
Disassembly of section .text:
00000000 <foo>:
0: e92d4800 push {fp, lr}
4: e1a0b00d mov fp, sp
8: ebfffffe bl 0 <_mcount> // _mcount should not be generated
c: e8bd8800 pop {fp, pc}</pre>
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