riscv, bpf: Add support for far branching when emitting tail call

Start use the emit_branch() function in the tail call emitter in order
to support far branching.

Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191216091343.23260-4-bjorn.topel@gmail.com

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index e599458..c38c95d 100644 (file)
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -496,16 +496,6 @@ static int is_12b_check(int off, int insn)
        return 0;
 }
 
-static int is_13b_check(int off, int insn)
-{
-       if (!is_13b_int(off)) {
-               pr_err("bpf-jit: insn=%d 13b < offset=%d not supported yet!\n",
-                      insn, (int)off);
-               return -1;
-       }
-       return 0;
-}
-
 static int is_21b_check(int off, int insn)
 {
        if (!is_21b_int(off)) {
@@ -744,18 +734,14 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
                return -1;
        emit(rv_lwu(RV_REG_T1, off, RV_REG_A1), ctx);
        off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
-       if (is_13b_check(off, insn))
-               return -1;
-       emit(rv_bgeu(RV_REG_A2, RV_REG_T1, off >> 1), ctx);
+       emit_branch(BPF_JGE, RV_REG_A2, RV_REG_T1, off, ctx);
 
        /* if (--TCC < 0)
         *     goto out;
         */
        emit(rv_addi(RV_REG_T1, tcc, -1), ctx);
        off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
-       if (is_13b_check(off, insn))
-               return -1;
-       emit(rv_blt(RV_REG_T1, RV_REG_ZERO, off >> 1), ctx);
+       emit_branch(BPF_JSLT, RV_REG_T1, RV_REG_ZERO, off, ctx);
 
        /* prog = array->ptrs[index];
         * if (!prog)
@@ -768,9 +754,7 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
                return -1;
        emit(rv_ld(RV_REG_T2, off, RV_REG_T2), ctx);
        off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
-       if (is_13b_check(off, insn))
-               return -1;
-       emit(rv_beq(RV_REG_T2, RV_REG_ZERO, off >> 1), ctx);
+       emit_branch(BPF_JEQ, RV_REG_T2, RV_REG_ZERO, off, ctx);
 
        /* goto *(prog->bpf_func + 4); */
        off = offsetof(struct bpf_prog, bpf_func);