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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Consider forbidding non-constant expressions in offsetof"
href="https://bugs.llvm.org/show_bug.cgi?id=48407">48407</a>
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<th>Summary</th>
<td>Consider forbidding non-constant expressions in offsetof
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>unspecified
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>slyfox@inbox.ru
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>gcc-11 will deliberately become stricter and will disallow non-constant
expressions in offsetof: <a href="https://gcc.gnu.org/PR95942">https://gcc.gnu.org/PR95942</a>
Complete example:
// $ cat.bug.cc
struct a {
int b;
char c[100];
};
unsigned long d(long e) { return __builtin_offsetof(a, c[e]); }
$ g++-11.0.0 -c bug.cc -o bug.o
bug.cc: In function 'long unsigned int d(long int)':
bug.cc:6:60: error: 'e' is not a constant expression
6 | unsigned long d(long e) { return __builtin_offsetof(a, c[e]); }
| ^
$ clang++-11 -c bug.cc -o bug.o
<ok>
Should clang also reject the code above? If not should clang emit warning on
-Wall that non-standard extension is being used?
Thank you!</pre>
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