On Tue, Jun 21, 2022 at 11:30:32AM +0200, Stanisław Kardach wrote:
> On Tue, Jun 21, 2022 at 12:54 AM David Christensen
> <d...@linux.vnet.ibm.com> wrote:
> >
> > > On Thu, Jun 9, 2022 at 2:17 PM Stanislaw Kardach <k...@semihalf.com> 
> > > wrote:
> > >>
> > >> As David noticed in [1] there is an issue with C++ compilation of the
> > >> rte_vect.h header in RISC-V. Upon closer inspection, the problem appears 
> > >> on
> > >> all architectures due to the type conversion rules in C++.
> > >> More precisely a union type rte_xmm_t requires a conversion constructor
> > >> from xmm_t type.
> > >> The most obvious fix is to use a structure initializer for such copies
> > >> (since rte_xmm_t union contains xmm_t anyway). The generated assembly
> > >> at -O2 is exactly the same, so there's no real impact.
> > >>
> > >> The bigger question is whether accessing bits of the architecture 
> > >> specific
> > >> xmm_t type in an array fashion is always correct? All current 
> > >> architectures
> > >> define rte_xmm_t in the same manner implying that.
> > >
> > > Copying other arch maintainers.
> >
> > My read of the Altivec vector layout for LE systems says the existing
> > union operator rte_xmm_t is correct, though my C++ experience is
> > limited.  How can I generate an error with C++ to expose this issue?
> >
> > Dave
> To replicate this issue:
> 1. Apply the patch below. In essence it forces the use of scalar lpm
> and changes C++ compiler to g++ so that meson properly detects it.
> Otherwise C++ checks won't be generated.
> 2. Configure build with: meson build-ppc64le --werror --cross-file
> config/ppc/ppc64le-power8-linux-gcc-ubuntu -Dcheck_includes=true
> 3. Build with: ninja -C build-ppc64le buildtools/chkincs/chkincs-cpp
> 
> Note that the build target only gets generated if C++ compiler is
> properly discovered by meson. To be honest I'm not sure why
> powerpc64le-linux-gnu-cpp doesn't get properly picked up by meson.

Generally the "cpp" binary is not the c-plus-plus one, but the C
preprocessor one. Perhaps the original files are incorrect here, and should
all refer to g++.

/Bruce

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