stringop-overflow warning with GCC 14 #30114

Is there an existing issue for this?

• I have searched the existing issues

Current behaviour

When building with GCC 14, I noticed a new warning which is causing -Werror builds to fail

In file included from /usr/include/c++/14.1.1/string:51,
                 from ../../../src/crypto/sha256.h:10,
                 from ../../../src/hash.h:12,
                 from ../../../src/pubkey.h:10,
                 from ../../../src/addresstype.h:9,
                 from ../../../src/wallet/wallet.h:9,
                 from ../../../src/wallet/test/wallet_tests.cpp:5:
In function ‘constexpr typename __gnu_cxx::__enable_if<std::__is_scalar<_Tp>::__value, void>::__type std::__fill_a1(_ForwardIterator, _ForwardIterator, const _Tp&) [with _ForwardIterator = unsigned char*; _Tp = int]’,
    inlined from ‘constexpr void std::__fill_a1(__gnu_cxx::__normal_iterator<_Iterator, _Container>, __gnu_cxx::__normal_iterator<_Iterator, _Container>, const _Tp&) [with _Ite = unsigned char*; _Cont = vector<unsigned char>; _Tp = int]’ at /usr/include/c++/14.1.1/bits/stl_algobase.h:981:21,
    inlined from ‘constexpr void std::__fill_a(_FIte, _FIte, const _Tp&) [with _FIte = __gnu_cxx::__normal_iterator<unsigned char*, vector<unsigned char> >; _Tp = int]’ at /usr/include/c++/14.1.1/bits/stl_algobase.h:998:21,
    inlined from ‘constexpr void std::fill(_ForwardIterator, _ForwardIterator, const _Tp&) [with _ForwardIterator = __gnu_cxx::__normal_iterator<unsigned char*, vector<unsigned char> >; _Tp = int]’ at /usr/include/c++/14.1.1/bits/stl_algobase.h:1029:20,
    inlined from ‘void wallet::wallet_tests::PollutePubKey(CPubKey&)’ at ../../../src/wallet/test/wallet_tests.cpp:503:14:
/usr/include/c++/14.1.1/bits/stl_algobase.h:952:18: error: ‘void* __builtin_memset(void*, int, long unsigned int)’ specified bound 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
  952 |         *__first = __tmp;
      |         ~~~~~~~~~^~~~~~~
cc1plus: all warnings being treated as errors

Expected behaviour

Should build without warnings.

Steps to reproduce

Build with GCC 14.1.1

$ gcc --version
gcc (GCC) 14.1.1 20240507
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Relevant log output

No response

How did you obtain Bitcoin Core

Compiled from source

What version of Bitcoin Core are you using?

master@7a40f2a3f1cf744d136ecf534979114e79c5e71d

Operating system and version

Arch

Machine specifications

No response

I think might be a GCC bug, I can't figure out what is actually wrong with this code that would trigger the warning.

Looks like it derives that .begin() is the same as .end() which would bring the size to -1. This would require CPubKey::GetLen to return 0, which is possible if the first byte is invalid. Maybe it'd make sense to make it return 1 in that case because there's always the first byte?

Looks like it derives that .begin() is the same as .end() which would bring the size to -1. This would require CPubKey::GetLen to return 0, which is possible if the first byte is invalid. Maybe it'd make sense to make it return 1 in that case because there's always the first byte?

That worked, but since CPubKey is used in a ton of places, I'm a little bit hesitant to change GetLen since that may have unexpected side effects. However, I do have a fix that seems to work that changes to using insert() instead of std::fill.

Yes, could also handle it at another level, though it's strange for a class to return begin()==end() when there's actually one byte in it.

Edit: but yes it's too risky to change this just to work around a compiler warning in the tests.