https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105726
Bug ID: 105726
Summary: spurious warning with -Warray-bounds
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cuzdav at gmail dot com
Target Milestone: ---
Created attachment 53030
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53030&action=edit
preprocessed version
I just ran into an issue that seems to have appeared in Gcc 10.1 and is still
there in 11, 12, and in the trunk.
The following code produces a spurious warning about reading out of bounds,
but if I remove the "pad" field, or change from std::array to a "raw" array,
the warning goes away.
//===============================
#include <array>
#include <cstring>
struct X {
char pad[4];
std::array<char, 1> mField;
};
void encode(char* aBuffer, const X& aMessage) {
strncpy(aBuffer, aMessage.mField.data(), 1);
}
//===============================
LIVE: https://godbolt.org/z/zEsx5P8eP
<source>: In function 'void encode(char*, const X&)':
<source>:10:16: warning: 'char* strncpy(char*, const char*, size_t)' offset 4
from the object at 'aMessage' is out of the bounds of referenced subobject
'std::array<char, 1>::_M_elems' with type 'char [1]' at offset 4
[-Warray-bounds]
10 | strncpy(aBuffer, aMessage.mField.data(), 1);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from <source>:1:
/opt/compiler-explorer/gcc-12.1.0/include/c++/12.1.0/array:115:56: note:
subobject 'std::array<char, 1>::_M_elems' declared here
115 | typename _AT_Type::_Type _M_elems;
| ^~~~~~~~
Compiler returned: 0
OUTPUT of g++ -v
Using built-in specs.
COLLECT_GCC=/opt/imc/gcc-12.1.0/bin/g++
COLLECT_LTO_WRAPPER=/opt/imc/gcc-12.1.0/libexec/gcc/x86_64-pc-linux-gnu/12.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-12.1.0/configure --prefix=/opt/imc/gcc-12.1.0
--enable-languages=c,c++,fortran,lto --disable-multilib
--with-build-time-tools=/build/INSTALLDIR//opt/imc/gcc-12.1.0/bin
--enable-libstdcxx-time=rt
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.1.0 (GCC)
