8288759: GCC 12 fails to compile signature.cpp due to -Wstringop-overread

[shipilev]

Trying to compile with GCC 12.1.1 (current Fedora Rawhide) yields this failure:

In file included from /home/test/shipilev-jdk/src/hotspot/share/utilities/globalDefinitions_gcc.hpp:35,
                 from /home/test/shipilev-jdk/src/hotspot/share/utilities/globalDefinitions.hpp:35,
                 from /home/test/shipilev-jdk/src/hotspot/share/memory/allocation.hpp:29,
                 from /home/test/shipilev-jdk/src/hotspot/share/classfile/classLoaderData.hpp:28,
                 from /home/test/shipilev-jdk/src/hotspot/share/precompiled/precompiled.hpp:34:
In function 'const void* memchr(const void*, int, size_t)',
    inlined from 'int SignatureStream::scan_type(BasicType)' at /home/test/shipilev-jdk/src/hotspot/share/runtime/signature.cpp:343:32,
    inlined from 'void SignatureStream::next()' at /home/test/shipilev-jdk/src/hotspot/share/runtime/signature.cpp:373:19,
    inlined from 'void SignatureIterator::do_parameters_on(T*) [with T = Fingerprinter]' at /home/test/shipilev-jdk/src/hotspot/share/runtime/signature.hpp:635:41,
    inlined from 'void SignatureIterator::do_parameters_on(T*) [with T = Fingerprinter]' at /home/test/shipilev-jdk/src/hotspot/share/runtime/signature.hpp:629:6,
    inlined from 'void Fingerprinter::compute_fingerprint_and_return_type(bool)' at /home/test/shipilev-jdk/src/hotspot/share/runtime/signature.cpp:169:19:
/usr/include/string.h:102:27: error: 'void* __builtin_memchr(const void*, int, long unsigned int)' specified bound [18446744073709486082, 0] exceeds maximum object size 9223372036854775807 [-Werror=stringop-overread]
  102 |   return __builtin_memchr (__s, __c, __n);
      |          ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors

As @kimbarrett says: "The warning is indicating an actual problem with the code. The while loop on line 338 may terminate with end == limit if the string consists of just a sequence of '[' and then ends. If the loop ends for that reason, we later read base[limit], invoking UB as limit is the length of base."

Additional testing:

• Linux x86_64 fastdebug build with GCC 12.1.1
• Linux x86_64 fastdebug build with GCC 9.4.0

---

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Issue

• JDK-8288759: GCC 12 fails to compile signature.cpp due to -Wstringop-overread

Reviewers

• Coleen Phillimore (@coleenp - Reviewer) ⚠️ Review applies to e74cede8

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[openjdk]

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[mlbridge]

Webrevs

• 01: Full - Incremental (8209c0aa)
• 00: Full (e74cede8)

[shipilev]

Any takers? :)

[coleenp]

Seems fine.

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8288759: GCC 12 fails to compile signature.cpp due to -Wstringop-overread

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[shipilev]

Seems fine.

Thanks! @kimbarrett, want to take a look as well?

[shipilev]

@kimbarrett, @coleenp -- I redid the fix to fix the actual warning instead. I opted to return limit on the failure path + assert it does not actually happen in practice. It looks that returning limit is acceptable, as it rolls over to the "end of signature" on error. We can make that fatal() instead, but I don't like to penalize release builds unnecessarily.

[kimbarrett]

The proposed fix seems plausible, and addresses the warning. I was a little worried that someone might come along later and try to change it to just

assert(end < limit, "invalid type");

but presumably that will get the warning again during testing.

I tried to think of a less contrived way to write this while still addressing the warning. I haven't come up with anything better, assuming returning limit is okay.

But I'm entirely unfamiliar with the signature code, so don't know if returning limit is okay. So don't count me as a reviewer for this change (and I won't hit the Approve button).

[shipilev]

Closed in favor of openjdk/jdk#9711