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

[Kim Barrett]

On Mon, 20 Jun 2022 17:58:49 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> 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:

Changes requested by kbarrett (Reviewer).

src/hotspot/share/runtime/signature.cpp line 328:

> 326: 
> 327: PRAGMA_DIAG_PUSH
> 328: PRAGMA_STRINGOP_OVERREAD_IGNORED

Don't make this change.  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.  As a proof of concept, adding

if (end >= limit) return limit;

after the while loop makes the warning go away.  I have no idea what the correct thing to do for this might be.  Returning limit might be wrong; I just used that to verify this issue is the source of the warning.

src/hotspot/share/utilities/compilerWarnings_gcc.hpp line 60:

> 58: #if !defined(__clang_major__) && (__GNUC__ >= 8)
> 59: #define PRAGMA_STRINGOP_TRUNCATION_IGNORED PRAGMA_DISABLE_GCC_WARNING("-Wstringop-truncation")
> 60: #endif

Why was `PRAGMA_STRINGOP_TRUNCATION` moved?  Oh, I see, you are reordering based on version.  I'd rather all three of these `-Wstringop-xxx` were together, perhaps sorted alphabetically.  I don't see the use of a version ordering.  So my preference would be that this part of the change wasn't made.

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PR: https://git.openjdk.org/jdk19/pull/49