build warning: fortify memcpy

jsarenik commented at 9:35 pm on November 30, 2021: none

This is just a warning, but want to make a note here.

 0  CXX      libbitcoin_server_a-signet.o
 1In file included from /usr/include/c++/10.3.1/cstring:42,
 2                 from ./uint256.h:10,
 3                 from ./consensus/params.h:9,
 4                 from ./signet.h:8,
 5                 from signet.cpp:5:
 6In function 'void* memcpy(void*, const void*, size_t)',
 7    inlined from 'void CVectorWriter::write(const char*, size_t)' at ./streams.h:102:19,
 8    inlined from 'void base_blob<BITS>::Serialize(Stream&) const [with Stream = CVectorWriter; unsigned int BITS = 256]' at ./uint256.h:99:16,
 9    inlined from 'static std::optional<SignetTxs> SignetTxs::Create(const CBlock&, const CScript&)' at ./serialize.h:670:16:
10/usr/include/fortify/string.h:53:25: warning: 'void* __builtin_memcpy(void*, const void*, long unsigned int)' writing between 1 and 32 bytes into a region of size 0 overflows the destination [-Wstringop-overflow=]
11   53 |  return __builtin_memcpy(__od, __os, __n);
12      |         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~

Expected behavior

Clean happy compilation, something like this which comes from later output:

0...
1  CXX      wallet/libbitcoin_wallet_a-db.o
2  CXX      wallet/libbitcoin_wallet_a-dump.o
3  CXX      wallet/libbitcoin_wallet_a-external_signer_scriptpubkeyman.o
4  CXX      wallet/libbitcoin_wallet_a-feebumper.o
5  CXX      wallet/libbitcoin_wallet_a-fees.o
6  CXX      wallet/libbitcoin_wallet_a-interfaces.o
7...

Actual behavior

Warnings during make.

To reproduce

 0# On Alpine Linux (musl-libc)
 1export CFLAGS="-pipe -s -march=native -mtune=native -O3"
 2export LDFLAGS="-s -no-pie"
 3
 4test -x ./configure || ./autogen.sh
 5./configure \
 6  --without-gui \
 7  --with-incompatible-bdb \
 8  --disable-tests \
 9  --disable-bench \
10  --disable-zmq \
11  --disable-hardening \
12  CFLAGS="$CFLAGS" \
13  CXXFLAGS="$CFLAGS" \
14  LDFLAGS="$LDFLAGS"
15make prefix=$HOME/bitcoin-latest install

System information

Alpine Linux (musl-libc x86_64)

0$ uname -mr
15.10.61-0-lts x86_64

Self-compiled Bitcoin Core exactly from jsarenik/bitcoin@878d8e1c0

This warning was experienced while compiling version of bitcoin to test #23531 while also rebasing #22563 on top of it and also Alpine Linux locales patch.

All the rebasing was trivial and maybe the warning is showing for longer but now I noticed it for the first time.

jsarenik added the label Bug on Nov 30, 2021

MarcoFalke commented at 12:53 pm on December 13, 2021: member

Looks like a compiler bug

MarcoFalke added the label Upstream on Dec 13, 2021

MarcoFalke commented at 12:54 pm on December 13, 2021: member

For reference, the function is:

 0    void write(const char* pch, size_t nSize)
 1    {
 2        assert(nPos <= vchData.size());
 3        size_t nOverwrite = std::min(nSize, vchData.size() - nPos);
 4        if (nOverwrite) {
 5            memcpy(vchData.data() + nPos, reinterpret_cast<const unsigned char*>(pch), nOverwrite);
 6        }
 7        if (nOverwrite < nSize) {
 8            vchData.insert(vchData.end(), reinterpret_cast<const unsigned char*>(pch) + nOverwrite, reinterpret_cast<const unsigned char*>(pch) + nSize);
 9        }
10        nPos += nSize;
11    }

fanquake commented at 1:42 pm on December 13, 2021: member

Looks like a compiler bug

Yes I think so. Reproduced with GCC 10.3.1 (on Alpine), with -O3, no warning with -O2. Possibly https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94335 or related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92955.

Not much we can do here, other than suggest you up/downgrade to a non-buggy compiler.

Going to close for now.

fanquake closed this on Dec 13, 2021

DrahtBot locked this on Dec 13, 2022

build warning: fortify memcpy #23638