Re: [dpdk-dev] [PATCH v11 1/3] eal/arm64: add 128-bit atomic compare exchange

[David Marchand <david.marchand@redhat.com>]

On Fri, Oct 18, 2019 at 1:22 PM Phil Yang <phil.yang@arm.com> wrote:
>
> This patch adds the implementation of the 128-bit atomic compare
> exchange API on AArch64. Using 64-bit 'ldxp/stxp' instructions
> can perform this operation. Moreover, on the LSE atomic extension
> accelerated platforms, it implemented by 'casp' instructions for
> better performance.
>
> Since the '__ARM_FEATURE_ATOMICS' flag only supports GCC-9, so this
> patch adds a new config flag 'RTE_ARM_FEATURE_ATOMICS' to enable the
> 'cas' version on elder version compilers.

Jerin, Phil,

I am getting a build error on the octeontx2 target:

{standard input}: Assembler messages:
{standard input}:672: Error: selected processor does not support `casp
x0,x1,x2,x3,[x4]'
{standard input}:690: Error: selected processor does not support
`caspa x0,x1,x2,x3,[x4]'
{standard input}:708: Error: selected processor does not support
`caspl x0,x1,x2,x3,[x4]'
{standard input}:726: Error: selected processor does not support
`caspal x0,x1,x2,x3,[x4]'
ninja: build stopped: subcommand failed.

Looking into the meson logs, I can see:

Native C compiler: ccache gcc (gcc 9.2.1 "gcc (GCC) 9.2.1 20190827
(Red Hat 9.2.1-1)")
Cross C compiler: aarch64-linux-gnu-gcc (gcc 8.2.1)
Host machine cpu family: aarch64
Host machine cpu: armv8-a
Target machine cpu family: aarch64
Target machine cpu: armv8-a
Build machine cpu family: x86_64
Build machine cpu: x86_64
...
Message: Implementer : Cavium
Compiler for C supports arguments -mcpu=octeontx2: NO
Message: []
Fetching value of define "__ARM_NEON" : 1
Fetching value of define "__ARM_FEATURE_CRC32" :
Fetching value of define "__ARM_FEATURE_CRYPTO" :


My toolchain does not support the octeontx2 target, but
RTE_ARM_FEATURE_ATOMICS ends up being set in the configuration anyway.
Tried with Linaro toolchains (4.7.1, 7.4) mentionned in the dpdk
documentation, same result.

Looking at config/arm/meson.build, the "extra machine specific flags"
are appended to the configuration, regardless of what the compiler
replied when testing the machine args.

-- 
David Marchand