AMReX_FabConv.cpp warning writing 1 byte into a region of size 0 [-Wstringop-overflow=]

[tanweihou]

Dear AMReX developers,
cc: @ax3l
I am a WarpX user in NERSC.
I observed the following warning message when I was building WarpX in Perlmutter.

In function 'void amrex::_pd_btrvout(char*, amrex::Long, amrex::Long)',
    inlined from 'void amrex::_pd_insert_field(amrex::Long, int, char*, int, int, int)' at /build2204-hdf5/_deps/fetchedamrex-src/Src/Base/AMReX_FabConv.cpp:462:12,
    inlined from 'void amrex::PD_fconvert(void*, const void*, amrex::Long, int, const Long*, const int*, const Long*, const int*, int, int, int)' at /build2204-hdf5/_deps/fetchedamrex-src/Src/Base/AMReX_FabConv.cpp:743:17:
/build2204-hdf5/_deps/fetchedamrex-src/Src/Base/AMReX_FabConv.cpp:393:7: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  393 |             *p2 = tmp;
      |       ^
/build2204-hdf5/_deps/fetchedamrex-src/Src/Base/AMReX_FabConv.cpp: In function 'void amrex::PD_fconvert(void*, const void*, amrex::Long, int, const Long*, const int*, const Long*, const int*, int, int, int)':
/build2204-hdf5/_deps/fetchedamrex-src/Src/Base/AMReX_FabConv.cpp:612:6: note: at offset [9, 1073741822] into destination object 'in_long' of size 8
  612 | PD_fconvert (void*       out,

Here's the list of modules that I use in Perlmutter.

Currently Loaded Modules:
  1) craype-x86-milan                      10) craype/2.7.15
  2) libfabric/1.11.0.4.114                11) cray-dsmml/0.2.2
  3) craype-network-ofi                    12) cray-mpich/8.1.15
  4) perftools-base/22.04.0                13) cray-libsci/21.08.1.2
  5) xpmem/2.3.2-2.2_7.5__g93dd7ee.shasta  14) PrgEnv-gnu/8.3.3
  6) xalt/2.10.2                           15) Nsight-Compute/2022.1.1
  7) darshan/3.3.1                         16) Nsight-Systems/2022.2.1
  8) cmake/3.22.0                          17) cudatoolkit/11.5
  9) gcc/11.2.0                            18) cray-hdf5-parallel/1.12.1.1

Thank you.

[Thierry992]

Have the same issue on Perlmutter

[WeiqunZhang]

I can reproduce the warnings on Perlmutter when compiling with cmake. However, there are no such warnings with gnu make (with -Wall -Wstringop-overflow). The difference seems to be that in gnu make nvcc -ccbin=g++ is used, whereas in cmake nvcc -ccbin=CC is used.

[WeiqunZhang]

It is due to that the CC wrapper adds -march=znver3 to g++.

[WeiqunZhang]

-O3 -march=znver3 produces the warnings, but -O2 -march=znver3 does not.

[WeiqunZhang]

The warnings are false positive, but we can fix them.