Hi Ben, > -----Original Message----- > From: ben.dooks@xxxxxxxxxxxxxxx <ben.dooks@xxxxxxxxxxxxxxx> > Sent: Tuesday, May 7, 2024 10:00 PM > To: Pu Lehui <pulehui@xxxxxxxxxx>; Wang, Xiao W > <xiao.w.wang@xxxxxxxxx>; paul.walmsley@xxxxxxxxxx; palmer@xxxxxxxxxxx; > aou@xxxxxxxxxxxxxxxxx; luke.r.nels@xxxxxxxxx; xi.wang@xxxxxxxxx; > bjorn@xxxxxxxxxx > Cc: ast@xxxxxxxxxx; daniel@xxxxxxxxxxxxx; andrii@xxxxxxxxxx; > martin.lau@xxxxxxxxx; eddyz87@xxxxxxxxx; song@xxxxxxxxxx; > yonghong.song@xxxxxxxxx; john.fastabend@xxxxxxxxx; kpsingh@xxxxxxxxxx; > sdf@xxxxxxxxxx; haoluo@xxxxxxxxxx; jolsa@xxxxxxxxxx; linux- > riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx; > Li, Haicheng <haicheng.li@xxxxxxxxx> > 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@xxxxxxxxx> > >> --- > >> 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
