[PATCH bpf v2 4/5] bpf: Add kernel function call support in 32-bit ARM for EABI

Yang Jihong
2022-11-07T09:24:17Z

This patch adds kernel function call support to 32-bit ARM bpf jit for
EABI.

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
---
arch/arm/net/bpf_jit_32.c | 142 ++++++++++++++++++++++++++++++++++++++
1 file changed, 142 insertions(+)

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 6a1c9fca5260..9c0e1c22dc37 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -1337,6 +1337,130 @@ static void build_epilogue(struct jit_ctx *ctx)
#endif
}

+/*
+ * Input parameters of function in 32-bit ARM architecture:
+ * The first four word-sized parameters passed to a function will be
+ * transferred in registers R0-R3. Sub-word sized arguments, for example,
+ * char, will still use a whole register.
+ * Arguments larger than a word will be passed in multiple registers.
+ * If more arguments are passed, the fifth and subsequent words will be passed
+ * on the stack.
+ *
+ * The first for args of a function will be considered for
+ * putting into the 32bit register R1, R2, R3 and R4.
+ *
+ * Two 32bit registers are used to pass a 64bit arg.
+ *
+ * For example,
+ * void foo(u32 a, u32 b, u32 c, u32 d, u32 e):
+ * u32 a: R0
+ * u32 b: R1
+ * u32 c: R2
+ * u32 d: R3
+ * u32 e: stack
+ *
+ * void foo(u64 a, u32 b, u32 c, u32 d):
+ * u64 a: R0 (lo32) R1 (hi32)
+ * u32 b: R2
+ * u32 c: R3
+ * u32 d: stack
+ *
+ * void foo(u32 a, u64 b, u32 c, u32 d):
+ * u32 a: R0
+ * u64 b: R2 (lo32) R3 (hi32)
+ * u32 c: stack
+ * u32 d: stack
+ *
+ * void foo(u32 a, u32 b, u64 c, u32 d):
+ * u32 a: R0
+ * u32 b: R1
+ * u64 c: R2 (lo32) R3 (hi32)
+ * u32 d: stack
+ *
+ * void foo(u64 a, u64 b):
+ * u64 a: R0 (lo32) R1 (hi32)
+ * u64 b: R2 (lo32) R3 (hi32)
+ *
+ * The return value will be stored in the R0 (and R1 for 64bit value).
+ *
+ * For example,
+ * u32 foo(u32 a, u32 b, u32 c):
+ * return value: R0
+ *
+ * u64 foo(u32 a, u32 b, u32 c):
+ * return value: R0 (lo32) R1 (hi32)
+ *
+ * The above is for AEABI only, OABI does not support this function.
+ */
+static int emit_kfunc_call(const struct bpf_insn *insn, struct jit_ctx *ctx, const u32 func)
+{
+ int i;
+ const struct btf_func_model *fm;
+ const s8 *tmp = bpf2a32[TMP_REG_1];
+ const u8 arg_regs[] = { ARM_R0, ARM_R1, ARM_R2, ARM_R3 };
+ int nr_arg_regs = ARRAY_SIZE(arg_regs);
+ int arg_regs_idx = 0, stack_off = 0;
+ const s8 *rd;
+ s8 rt;
+
+ if (!IS_ENABLED(CONFIG_AEABI)) {
+ pr_info_once("kfunc call only support for AEABI in 32-bit arm\n");
+ return -EINVAL;
+ }
+
+ fm = bpf_jit_find_kfunc_model(ctx->prog, insn);
+ if (!fm)
+ return -EINVAL;
+
+ for (i = 0; i < fm->nr_args; i++) {
+ if (fm->arg_size[i] > sizeof(u32)) {
+ rd = arm_bpf_get_reg64(bpf2a32[BPF_REG_1 + i], tmp, ctx);
+
+ if (arg_regs_idx + 1 < nr_arg_regs) {
+ /*
+ * AAPCS states:
+ * A double-word sized type is passed in two
+ * consecutive registers (e.g., r0 and r1, or
+ * r2 and r3). The content of the registers is
+ * as if the value had been loaded from memory
+ * representation with a single LDM instruction.
+ */
+ if (arg_regs_idx & 1)
+ arg_regs_idx++;
+
+ emit(ARM_MOV_R(arg_regs[arg_regs_idx++], rd[1]), ctx);
+ emit(ARM_MOV_R(arg_regs[arg_regs_idx++], rd[0]), ctx);
+ } else {
+ stack_off = ALIGN(stack_off, STACK_ALIGNMENT);
+
+ if (__LINUX_ARM_ARCH__ >= 6 ||
+ ctx->cpu_architecture >= CPU_ARCH_ARMv5TE) {
+ emit(ARM_STRD_I(rd[1], ARM_SP, stack_off), ctx);
+ } else {
+ emit(ARM_STR_I(rd[1], ARM_SP, stack_off), ctx);
+ emit(ARM_STR_I(rd[0], ARM_SP, stack_off), ctx);
+ }
+
+ stack_off += 8;
+ }
+ } else {
+ rt = arm_bpf_get_reg32(bpf2a32[BPF_REG_1 + i][1], tmp[1], ctx);
+
+ if (arg_regs_idx < nr_arg_regs) {
+ emit(ARM_MOV_R(arg_regs[arg_regs_idx++], rt), ctx);
+ } else {
+ emit(ARM_STR_I(rt, ARM_SP, stack_off), ctx);
+ stack_off += 4;
+ }
+ }
+ }
+
+ emit_a32_mov_i(tmp[1], func, ctx);
+ emit_blx_r(tmp[1], ctx);
+
+ return 0;
+}
+
/*
* Convert an eBPF instruction to native instruction, i.e
* JITs an eBPF instruction.
@@ -1603,6 +1727,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
case BPF_LDX | BPF_MEM | BPF_H:
case BPF_LDX | BPF_MEM | BPF_B:
case BPF_LDX | BPF_MEM | BPF_DW:
+ case BPF_LDX | BPF_PROBE_MEM | BPF_W:
+ case BPF_LDX | BPF_PROBE_MEM | BPF_H:
+ case BPF_LDX | BPF_PROBE_MEM | BPF_B:
+ case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
rn = arm_bpf_get_reg32(src_lo, tmp2[1], ctx);
emit_ldx_r(dst, rn, off, ctx, BPF_SIZE(code));
break;
@@ -1785,6 +1913,16 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
const s8 *r5 = bpf2a32[BPF_REG_5];
const u32 func = (u32)__bpf_call_base + (u32)imm;

+ if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
+ int err;
+
+ err = emit_kfunc_call(insn, ctx, func);
+
+ if (err)
+ return err;
+ break;
+ }
+
emit_a32_mov_r64(true, r0, r1, ctx);
emit_a32_mov_r64(true, r1, r2, ctx);
emit_push_r64(r5, ctx);
@@ -2022,3 +2160,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
return prog;
}

+bool bpf_jit_supports_kfunc_call(void)
+{
+ return true;
+}
--
2.30.GIT