On 09/12/2024 10:26, Simone Magnani wrote:
> This patch introduces a new probe to check whether the kernel supports
> instruction set extensions v4. The v4 extension comprises several new
> instructions: BPF_{SDIV,SMOD} (signed div and mod), BPF_{LD,LDX,ST,STX,MOV}
> (sign-extended load/store/move), 32-bit BPF_JA (unconditional jump),
> target-independent BPF_ALU64 BSWAP (byte-swapping 16/32/64). These have
> been introduced in the following commits respectively:
>
> * ec0e2da ("bpf: Support new signed div/mod instructions.")
> * 1f9a1ea ("bpf: Support new sign-extension load insns")
> * 8100928 ("bpf: Support new sign-extension mov insns")
> * 4cd58e9 ("bpf: Support new 32bit offset jmp instruction")
> * 0845c3d ("bpf: Support new unconditional bswap instruction")
>
> Support in bpftool for previous ISA extensions were added in commit
> 0fd800b2 ("bpftool: Probe for instruction set extensions"). These probes
> are useful for userspace BPF projects that want to use newer
> instruction set extensions on newer kernels, to reduce the programs'
> sizes or their complexity. LLVM provides the mcpu=v4 option since commit
> "[BPF] support for BPF_ST instruction in codegen"
> (https://github.com/llvm/llvm-project/commit/8f28e8069c4ba1110daee8bddc4d5049b6d4646e).
>
> Signed-off-by: Simone Magnani <simone.magnani@xxxxxxxxxxxxx>
> ---
> tools/bpf/bpftool/feature.c | 23 +++++++++++++++++++++++
> tools/include/linux/filter.h | 10 ++++++++++
> 2 files changed, 33 insertions(+)
>
> diff --git a/tools/bpf/bpftool/feature.c b/tools/bpf/bpftool/feature.c
> index 4dbc4fcdf473..24fecdf8e430 100644
> --- a/tools/bpf/bpftool/feature.c
> +++ b/tools/bpf/bpftool/feature.c
> @@ -885,6 +885,28 @@ probe_v3_isa_extension(const char *define_prefix, __u32 ifindex)
> "V3_ISA_EXTENSION");
> }
>
> +/*
> + * Probe for the v4 instruction set extension introduced in commit 1f9a1ea821ff
> + * ("bpf: Support new sign-extension load insns").
> + */
> +static void
> +probe_v4_isa_extension(const char *define_prefix, __u32 ifindex)
> +{
> + struct bpf_insn insns[5] = {
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_JMP32_IMM(BPF_JEQ, BPF_REG_0, 1, 1),
> + BPF_JMP32_A(1),
> + BPF_MOV64_IMM(BPF_REG_0, 1),
> + BPF_EXIT_INSN()
> + };
> +
> + probe_misc_feature(insns, ARRAY_SIZE(insns),
> + define_prefix, ifindex,
> + "have_v4_isa_extension",
> + "ISA extension v4",
> + "V4_ISA_EXTENSION");
> +}
> +
> static void
> section_system_config(enum probe_component target, const char *define_prefix)
> {
> @@ -1029,6 +1051,7 @@ static void section_misc(const char *define_prefix, __u32 ifindex)
> probe_bounded_loops(define_prefix, ifindex);
> probe_v2_isa_extension(define_prefix, ifindex);
> probe_v3_isa_extension(define_prefix, ifindex);
> + probe_v4_isa_extension(define_prefix, ifindex);
> print_end_section();
> }
>
> diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
> index 65aa8ce142e5..a2962fc56f27 100644
> --- a/tools/include/linux/filter.h
> +++ b/tools/include/linux/filter.h
> @@ -75,6 +75,16 @@
> .off = 0, \
> .imm = LEN })
>
> +/* Unconditional jumps, gotol pc + imm32 */
> +
> +#define BPF_JMP32_A(IMM) \
> + ((struct bpf_insn) { \
> + .code = BPF_JMP32 | BPF_JA, \
> + .dst_reg = 0, \
> + .src_reg = 0, \
> + .off = 0, \
> + .imm = IMM })
> +
> /* Short form of mov, dst_reg = src_reg */
>
> #define BPF_MOV64_REG(DST, SRC) \
Nit: Can you please move this macro after BPF_JMP_A() in filter.h, so
that it remains consistent with the order in include/linux/filter.h?
The bpftool change looks good, thanks!
Please Cc other BPF maintainers too for bpftool patches.
Quentin
