[PATCH v2 2/2] bpf/arm64: support packet data load instructions

Christophe Fontaine
2026-03-19T11:45:45Z

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.

Both 'fast path' and 'slow path' are implemented, similar to
the x86_64 JIT, where we call '__rte_pktmbuf_read' if the
requested data is not in the first segment.

Added unit test which focuses only on BPF_LD | BPF_ABS/BPF_IND and
a BPF_LD | BPF_ABS slow path call.

Signed-off-by: Christophe Fontaine <cfontain@redhat.com>
---
app/test/test_bpf.c | 121 ++++++++++++++++++++++++++++++++++++++++
lib/bpf/bpf_jit_arm64.c | 86 ++++++++++++++++++++++++++++
2 files changed, 207 insertions(+)

diff --git a/app/test/test_bpf.c b/app/test/test_bpf.c
index dd24722450..799f9d30ca 100644
--- a/app/test/test_bpf.c
+++ b/app/test/test_bpf.c
@@ -2750,6 +2750,79 @@ 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),
+ },
+};
+
+/* load mbuf (BPF_ABS/BPF_IND) test-cases */
+static const struct ebpf_insn test_ld_slow_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 from chained mbuf */
+ {
+ .code = (BPF_LD | BPF_ABS | BPF_B),
+ /* 201: second mbuf, built by test_ld_mbuf1_prepare */
+ .imm = 201 + 0x42,
+ },
+ {
+ .code = (BPF_JMP | EBPF_EXIT),
+ },
+};
+
+static const struct ebpf_insn test_ld_ind_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,
+ },
+ {
+ /* Set return value to one. */
+ .code = (EBPF_ALU64 | EBPF_MOV | BPF_K),
+ .dst_reg = EBPF_REG_0,
+ .imm = 0,
+ },
+ /* load IPv4 version and IHL */
+ {
+ .code = (BPF_LD | BPF_IND | BPF_B),
+ .src_reg = EBPF_REG_0,
+ .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);
+}
+
+static int
+test_ld_slow_mbuf0_check(uint64_t rc, const void *arg)
+{
+ return cmp_res(__func__, 0x42, rc, arg, arg, 0);
+}
+
/* load mbuf (BPF_ABS/BPF_IND) test-cases */
static const struct ebpf_insn test_ld_mbuf1_prog[] = {

@@ -3417,6 +3490,54 @@ 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_abs_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_slow_mbuf0",
+ .arg_sz = sizeof(struct dummy_mbuf),
+ .prm = {
+ .ins = test_ld_slow_mbuf0_prog,
+ .nb_ins = RTE_DIM(test_ld_slow_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_slow_mbuf0_check,
+ /* mbuf as input argument is not supported on 32 bit platform */
+ .allow_fail = (sizeof(uint64_t) != sizeof(uintptr_t)),
+ },
+ {
+ .name = "test_ld_ind_mbuf0",
+ .arg_sz = sizeof(struct dummy_mbuf),
+ .prm = {
+ .ins = test_ld_ind_mbuf0_prog,
+ .nb_ins = RTE_DIM(test_ld_ind_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),
diff --git a/lib/bpf/bpf_jit_arm64.c b/lib/bpf/bpf_jit_arm64.c
index 099822e9f1..5b3b80cb86 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"

@@ -1123,6 +1124,75 @@ emit_branch(struct a64_jit_ctx *ctx, uint8_t op, uint32_t i, int16_t off)
emit_b_cond(ctx, ebpf_to_a64_cond(op), jump_offset_get(ctx, i, off));
}

+/*
+ * Emit code for BPF_LD | BPF_ABS/IND: load from packet.
+ * Implements both a fast path, which computes the offset and read directly
+ * and a slow path, which calls __rte_pktmbuf_read(mbuf, off, len, buf)
+ * when the data is not in the first segment.
+ */
+static void
+emit_ld_mbuf(struct a64_jit_ctx *ctx, uint32_t op, uint8_t tmp1, uint8_t tmp2,
+ uint8_t src, int32_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);
+
+ /* 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, 0, A64_R(1), imm);
+ } else {
+ emit_mov_imm(ctx, 0, tmp2, imm);
+ emit_add(ctx, 0, tmp2, src);
+ emit_mov_64(ctx, A64_R(1), tmp2);
+ }
+
+ /* r2 = len, 1/2/4 bytes */
+ emit_mov_imm32(ctx, 0, A64_R(2), sz);
+ /* r3 = buf (SP) */
+ emit_mov_64(ctx, A64_R(3), A64_SP);
+
+ /* tmp1 = mbuf->data_len */
+ emit_mov_imm(ctx, 1, tmp1, offsetof(struct rte_mbuf, data_len));
+ emit_ldr(ctx, BPF_W, tmp1, r6, tmp1);
+
+ /* tmp2 = off + sz */
+ emit_add_imm_64(ctx, tmp2, A64_R(1), sz);
+ /* if off+sz > data_len, jump to slow path */
+ emit_cmp(ctx, 1, tmp2, tmp1);
+ emit_b_cond(ctx, A64_HI, 8);
+
+ /* Fast path, read directly, pointer to the data will be in A64_R(0) */
+ /* A64_R(0) = mbuf->buf_addr */
+ emit_mov_imm(ctx, 1, tmp1, offsetof(struct rte_mbuf, buf_addr));
+ emit_ldr(ctx, EBPF_DW, A64_R(0), r6, tmp1);
+ /* tmp2 = * mbuf->data_off */
+ emit_mov_imm(ctx, 1, tmp2, offsetof(struct rte_mbuf, data_off));
+ emit_ldr(ctx, BPF_H, tmp2, r6, tmp2);
+
+ /* A64_R(0) += data_off + off */
+ emit_add(ctx, 1, A64_R(0), tmp2);
+ emit_add(ctx, 1, A64_R(0), A64_R(1));
+
+ /* End of Fast Path, skip slow path */
+ emit_b(ctx, 4);
+
+ /* slow path, call __rte_pktmbuf_read */
+ emit_call(ctx, tmp1, __rte_pktmbuf_read);
+ /* check return value of __rte_pktmbuf_read */
+ emit_return_zero_if_src_zero(ctx, 1, A64_R(0));
+
+ /* A64_R(0) points to the data, load 1/2/4 bytes into r0*/
+ emit_ldr(ctx, opsz, r0, A64_R(0), A64_ZR);
+ if (sz != sizeof(uint8_t))
+ emit_be(ctx, r0, sz * CHAR_BIT);
+}
+
static void
check_program_has_call(struct a64_jit_ctx *ctx, struct rte_bpf *bpf)
{
@@ -1137,6 +1207,13 @@ 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 +1415,15 @@ 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