Messages in this thread | | | From | "Wang, Xiao W" <> | Subject | RE: [PATCH] riscv, bpf: Optimize zextw insn with Zba extension | Date | Thu, 9 May 2024 09:31:31 +0000 |
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Hi Ben,
> -----Original Message----- > From: ben.dooks@codethink.co.uk <ben.dooks@codethink.co.uk> > Sent: Tuesday, May 7, 2024 10:00 PM > To: Pu Lehui <pulehui@huawei.com>; Wang, Xiao W > <xiao.w.wang@intel.com>; paul.walmsley@sifive.com; palmer@dabbelt.com; > aou@eecs.berkeley.edu; luke.r.nels@gmail.com; xi.wang@gmail.com; > bjorn@kernel.org > Cc: ast@kernel.org; daniel@iogearbox.net; andrii@kernel.org; > martin.lau@linux.dev; eddyz87@gmail.com; song@kernel.org; > yonghong.song@linux.dev; john.fastabend@gmail.com; kpsingh@kernel.org; > sdf@google.com; haoluo@google.com; jolsa@kernel.org; linux- > riscv@lists.infradead.org; linux-kernel@vger.kernel.org; bpf@vger.kernel.org; > Li, Haicheng <haicheng.li@intel.com> > Subject: Re: [PATCH] riscv, bpf: Optimize zextw insn with Zba extension > > On 07/05/2024 13:47, Pu Lehui wrote: > > > > On 2024/5/7 18:45, Xiao Wang wrote: > >> The Zba extension provides add.uw insn which can be used to implement > >> zext.w with rs2 set as ZERO. > >> > >> Signed-off-by: Xiao Wang <xiao.w.wang@intel.com> > >> --- > >> arch/riscv/Kconfig | 19 +++++++++++++++++++ > >> arch/riscv/net/bpf_jit.h | 18 ++++++++++++++++++ > >> 2 files changed, 37 insertions(+) > >> > >> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > >> index 6bec1bce6586..0679127cc0ea 100644 > >> --- a/arch/riscv/Kconfig > >> +++ b/arch/riscv/Kconfig > >> @@ -586,6 +586,14 @@ config RISCV_ISA_V_PREEMPTIVE > >> preemption. Enabling this config will result in higher memory > >> consumption due to the allocation of per-task's kernel Vector > >> context. > >> +config TOOLCHAIN_HAS_ZBA > >> + bool > >> + default y > >> + depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zba) > >> + depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zba) > >> + depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900 > >> + depends on AS_HAS_OPTION_ARCH > >> + > >> config TOOLCHAIN_HAS_ZBB > > At this point would it be easier to ask the toolchain what's enabled > and put into kconfig via some sort of script?
You mean to use some sort of script to automatically detect whether LD linker can support a certain riscv extension?
I just went through the help guide of riscv64-linux-gnu-ld, and did some trial, the "--architecture" argument usage is different from the CC's "-march". I can't find other relevant args. It looks currently there's no direct method to dump the supported riscv extensions of a LD.
Then I tried below test to see if we can check it via building from /dev/null, just like the cc-option does. Note: here CC is Zbb capable CC -march=rv64gc_zbb -x c -c /dev/null -o tmp.o && LD tmp.o -o tmp.elf
I find that whether LD is Zbb capable or not, the above command just outputs "warning: cannot find entry symbol _start ..", no error comes with older LD. When we provide some Zbb-arch-tagged non-empty *.o file to the LD, then the older LD would error out "unsupported ISA subset ..". But I'm afraid it's not a good idea to add a source file for each extension detection.
Maybe in future there would be an easy way to ask the LD what riscv extensions are supported.
BRs, Xiao
> > -- > Ben Dooks http://www.codethink.co.uk/ > Senior Engineer Codethink - Providing Genius > > https://www.codethink.co.uk/privacy.html
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