bpftool: Probe for ISA v4 instruction set extension

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:

* ec0e2da95f72 ("bpf: Support new signed div/mod instructions.")
* 1f9a1ea821ff ("bpf: Support new sign-extension load insns")
* 8100928c8814 ("bpf: Support new sign-extension mov insns")
* 4cd58e9af8b9 ("bpf: Support new 32bit offset jmp instruction")
* 0845c3db7bf5 ("bpf: Support new unconditional bswap instruction")

Support in bpftool for previous ISA extensions was added in commit
0fd800b2456c ("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 LLVM commit 8f28e8069c4b ("[BPF]
support for BPF_ST instruction in codegen") [0].

Signed-off-by: Simone Magnani <simone.magnani@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <qmo@kernel.org>
Link: https://github.com/llvm/llvm-project/commit/8f28e8069c4ba1110daee8bddc4d5049b6d4646e
Link: https://lore.kernel.org/bpf/20241209145439.336362-1-simone.magnani@isovalent.com

diff --git a/tools/bpf/bpftool/feature.c b/tools/bpf/bpftool/feature.c
index 4dbc4fcdf47387a6023d62805a90ce96c295b4a8..24fecdf8e430780267a21aebd90dc07fc4d83e9d 100644 (file)
--- 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 65aa8ce142e598c943147ca5e47133f1db017d81..bcc6df79301aead69190edea3b000c965a5582ef 100644 (file)
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -273,6 +273,16 @@
                .off   = OFF,                                   \
                .imm   = 0 })
 
+/* 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 })
+
 /* Function call */
 
 #define BPF_EMIT_CALL(FUNC)                                    \