RE: [PATCH 1/5] config/riscv: add flag for using Zbc extension

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
1/5] config/riscv: add flag for using Zbc extension
> 
> On Tue, 18 Jun 2024 18:41:29 +0100
> Daniel Gregory <daniel.gregory@bytedance.com> wrote:
> 
> > diff --git a/config/riscv/meson.build b/config/riscv/meson.build
> > index 07d7d9da23..4bda4089bd 100644
> > --- a/config/riscv/meson.build
> > +++ b/config/riscv/meson.build
> > @@ -26,6 +26,13 @@ flags_common = [
> >      # read from /proc/device-tree/cpus/timebase-frequency. This property is
> >      # guaranteed on Linux, as riscv time_init() requires it.
> >      ['RTE_RISCV_TIME_FREQ', 0],
> > +
> > +    # Use RISC-V Carry-less multiplication extension (Zbc) for hardware
> > +    # implementations of CRC-32C (lib/hash/rte_crc_riscv64.h), CRC-32 and
> CRC-16
> > +    # (lib/net/net_crc_zbc.c). Requires intrinsics available in GCC 14.1.0+
> and
> > +    # Clang 18.1.0+
> > +    # Make sure to add '_zbc' to your target's -march below
> > +    ['RTE_RISCV_ZBC', false],
> >  ]
> 
> Please do not add more config options via compile flags.
> It makes it impossible for distros to ship one version.
> 
> Instead, detect at compile or runtime

Build time detection is not possible for cross builds.