[PATCH] bpf/arm64: support packet data load instructions

Christophe Fontaine
2026-03-16T19:12:49Z

arm64 jit compiler didn't support reading from a packet.
Enable arm64 JIT to generate native code for
(BPF_ABS | <size> | BPF_LD) and (BPF_IND | <size> | BPF_LD)
instructions.

Compared to the x86_64 HIT, only a "slow path" is implemented,
'__rte_pktmbuf_read' is systematically called.

Signed-off-by: Christophe Fontaine <cfontain@redhat.com>
---
app/test/test_bpf.c | 42 ++++++++++++++++++++++++++
lib/bpf/bpf_jit_arm64.c | 65 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 107 insertions(+)

diff --git a/app/test/test_bpf.c b/app/test/test_bpf.c
index 093cf5fe1d..8d5c0d6de1 100644
--- a/app/test/test_bpf.c
+++ b/app/test/test_bpf.c
@@ -2750,6 +2750,30 @@ static const struct rte_bpf_xsym test_call5_xsym[] = {
},
};

+/* load mbuf (BPF_ABS/BPF_IND) test-cases */
+static const struct ebpf_insn test_ld_mbuf0_prog[] = {
+ /* BPF_ABS/BPF_IND implicitly expect mbuf ptr in R6 */
+ {
+ .code = (EBPF_ALU64 | EBPF_MOV | BPF_X),
+ .dst_reg = EBPF_REG_6,
+ .src_reg = EBPF_REG_1,
+ },
+ /* load IPv4 version and IHL */
+ {
+ .code = (BPF_LD | BPF_ABS | BPF_B),
+ .imm = offsetof(struct rte_ipv4_hdr, version_ihl),
+ },
+ {
+ .code = (BPF_JMP | EBPF_EXIT),
+ },
+};
+
+static int
+test_ld_mbuf0_check(uint64_t rc, const void *arg)
+{
+ return cmp_res(__func__, 0x45, rc, arg, arg, 0);
+}
+
/* load mbuf (BPF_ABS/BPF_IND) test-cases */
static const struct ebpf_insn test_ld_mbuf1_prog[] = {

@@ -3417,6 +3441,22 @@ static const struct bpf_test tests[] = {
/* for now don't support function calls on 32 bit platform */
.allow_fail = (sizeof(uint64_t) != sizeof(uintptr_t)),
},
+ {
+ .name = "test_ld_mbuf0",
+ .arg_sz = sizeof(struct dummy_mbuf),
+ .prm = {
+ .ins = test_ld_mbuf0_prog,
+ .nb_ins = RTE_DIM(test_ld_mbuf0_prog),
+ .prog_arg = {
+ .type = RTE_BPF_ARG_PTR_MBUF,
+ .buf_size = sizeof(struct dummy_mbuf),
+ },
+ },
+ .prepare = test_ld_mbuf1_prepare,
+ .check_result = test_ld_mbuf0_check,
+ /* mbuf as input argument is not supported on 32 bit platform */
+ .allow_fail = (sizeof(uint64_t) != sizeof(uintptr_t)),
+ },
{
.name = "test_ld_mbuf1",
.arg_sz = sizeof(struct dummy_mbuf),
@@ -3491,6 +3531,7 @@ run_test(const struct bpf_test *tst)
if (ret != 0) {
printf("%s@%d: check_result(%s) failed, error: %d(%s);\n",
__func__, __LINE__, tst->name, ret, strerror(ret));
+ return -1;
}

/* repeat the same test with jit, when possible */
@@ -3506,6 +3547,7 @@ run_test(const struct bpf_test *tst)
"error: %d(%s);\n",
__func__, __LINE__, tst->name,
rv, strerror(rv));
+ return -1;
}
}

diff --git a/lib/bpf/bpf_jit_arm64.c b/lib/bpf/bpf_jit_arm64.c
index a04ef33a9c..5d5710b876 100644
--- a/lib/bpf/bpf_jit_arm64.c
+++ b/lib/bpf/bpf_jit_arm64.c
@@ -8,6 +8,7 @@

#include <rte_common.h>
#include <rte_byteorder.h>
+#include <rte_mbuf.h>

#include "bpf_impl.h"

@@ -965,6 +966,54 @@ emit_return_zero_if_src_zero(struct a64_jit_ctx *ctx, bool is64, uint8_t src)
emit_b(ctx, jump_to_epilogue);
}

+/*
+ * Emit code for BPF_LD | BPF_ABS/IND: load from packet.
+ * Calls __rte_pktmbuf_read(mbuf, off, len, buf).
+ */
+static void
+emit_ld_mbuf(struct a64_jit_ctx *ctx, uint32_t op, uint8_t tmp1, uint8_t tmp2,
+ uint8_t src, uint32_t imm)
+{
+ uint8_t r0 = ebpf_to_a64_reg(ctx, EBPF_REG_0);
+ uint8_t r6 = ebpf_to_a64_reg(ctx, EBPF_REG_6);
+ uint32_t mode = BPF_MODE(op);
+ uint32_t opsz = BPF_SIZE(op);
+ uint32_t sz = bpf_size(opsz);
+ int16_t jump_to_epilogue;
+
+ /* r0 = mbuf (R6) */
+ emit_mov_64(ctx, A64_R(0), r6);
+
+ /* r1 = off: for ABS use imm, for IND use src + imm */
+ if (mode == BPF_ABS) {
+ emit_mov_imm(ctx, 1, A64_R(1), imm);
+ } else {
+ emit_mov_imm(ctx, 1, tmp2, imm);
+ emit_add(ctx, 1, tmp2, src);
+ emit_mov_64(ctx, A64_R(1), tmp2);
+ }
+
+ /* r2 = len */
+ emit_mov_imm(ctx, 1, A64_R(2), sz);
+
+ /* r3 = buf (SP) */
+ emit_mov_64(ctx, A64_R(3), A64_SP);
+
+ /* call __rte_pktmbuf_read */
+ emit_call(ctx, tmp1, __rte_pktmbuf_read);
+ /* check return value of __rte_pktmbuf_read */
+ emit_cbnz(ctx, 1, A64_R(0), 3);
+ emit_mov_imm(ctx, 1, r0, 0);
+ jump_to_epilogue = (ctx->program_start + ctx->program_sz) - ctx->idx;
+ emit_b(ctx, jump_to_epilogue);
+
+ /* r0 points to the data, load 1/2/4 bytes */
+ emit_ldr(ctx, opsz, A64_R(0), A64_R(0), A64_ZR);
+ if (sz != sizeof(uint8_t))
+ emit_be(ctx, A64_R(0), sz * CHAR_BIT);
+ emit_mov_64(ctx, r0, A64_R(0));
+}
+
static void
emit_stadd(struct a64_jit_ctx *ctx, bool is64, uint8_t rs, uint8_t rn)
{
@@ -1137,6 +1186,13 @@ check_program_has_call(struct a64_jit_ctx *ctx, struct rte_bpf *bpf)
switch (op) {
/* Call imm */
case (BPF_JMP | EBPF_CALL):
+ /* BPF_LD | BPF_ABS/IND use __rte_pktmbuf_read */
+ case (BPF_LD | BPF_ABS | BPF_B):
+ case (BPF_LD | BPF_ABS | BPF_H):
+ case (BPF_LD | BPF_ABS | BPF_W):
+ case (BPF_LD | BPF_IND | BPF_B):
+ case (BPF_LD | BPF_IND | BPF_H):
+ case (BPF_LD | BPF_IND | BPF_W):
ctx->foundcall = 1;
return;
}
@@ -1338,6 +1394,15 @@ emit(struct a64_jit_ctx *ctx, struct rte_bpf *bpf)
emit_mov_imm(ctx, 1, dst, u64);
i++;
break;
+ /* load absolute/indirect from packet */
+ case (BPF_LD | BPF_ABS | BPF_B):
+ case (BPF_LD | BPF_ABS | BPF_H):
+ case (BPF_LD | BPF_ABS | BPF_W):
+ case (BPF_LD | BPF_IND | BPF_B):
+ case (BPF_LD | BPF_IND | BPF_H):
+ case (BPF_LD | BPF_IND | BPF_W):
+ emit_ld_mbuf(ctx, op, tmp1, tmp2, src, imm);
+ break;
/* *(size *)(dst + off) = src */
case (BPF_STX | BPF_MEM | BPF_B):
case (BPF_STX | BPF_MEM | BPF_H):
--
2.53.0