riscv, bpf: Optimize BPF tail calls

Remove one addi, and instead use the offset part of jalr.

Signed-off-by: Björn Töpel <bjorn.topel@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191216091343.23260-6-bjorn.topel@gmail.com

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index 2fc0f24..8aa19c8 100644 (file)
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -552,7 +552,7 @@ static int epilogue_offset(struct rv_jit_context *ctx)
        return (to - from) << 2;
 }
 
-static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
+static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
 {
        int stack_adjust = ctx->stack_size, store_offset = stack_adjust - 8;
 
@@ -589,9 +589,11 @@ static void __build_epilogue(u8 reg, struct rv_jit_context *ctx)
 
        emit(rv_addi(RV_REG_SP, RV_REG_SP, stack_adjust), ctx);
        /* Set return value. */
-       if (reg == RV_REG_RA)
+       if (!is_tail_call)
                emit(rv_addi(RV_REG_A0, RV_REG_A5, 0), ctx);
-       emit(rv_jalr(RV_REG_ZERO, reg, 0), ctx);
+       emit(rv_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
+                    is_tail_call ? 4 : 0), /* skip TCC init */
+            ctx);
 }
 
 /* return -1 or inverted cond */
@@ -751,9 +753,8 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
        if (is_12b_check(off, insn))
                return -1;
        emit(rv_ld(RV_REG_T3, off, RV_REG_T2), ctx);
-       emit(rv_addi(RV_REG_T3, RV_REG_T3, 4), ctx);
        emit(rv_addi(RV_REG_TCC, RV_REG_T1, 0), ctx);
-       __build_epilogue(RV_REG_T3, ctx);
+       __build_epilogue(true, ctx);
        return 0;
 }
 
@@ -1504,7 +1505,7 @@ static void build_prologue(struct rv_jit_context *ctx)
 
 static void build_epilogue(struct rv_jit_context *ctx)
 {
-       __build_epilogue(RV_REG_RA, ctx);
+       __build_epilogue(false, ctx);
 }
 
 static int build_body(struct rv_jit_context *ctx, bool extra_pass)