From db0a4b3b6b83a081a9ec309cc8178e5c9b4706a5 Mon Sep 17 00:00:00 2001 From: Jiong Wang Date: Fri, 1 Feb 2019 22:39:28 +0000 Subject: nfp: bpf: correct the behavior for shifts by zero Shifts by zero do nothing, and should be treated as nops. Even though compiler is not supposed to generate such instructions and manual written assembly is unlikely to have them, but they are legal instructions and have defined behavior. This patch correct existing shifts code-gen to make sure they do nothing when shift amount is zero except when the instruction is ALU32 for which high bits need to be cleared. For shift amount bigger than type size, already, NFP JIT back-end errors out for immediate shift and only low 5 bits will be taken into account for indirect shift which is the same as x86. Reviewed-by: Jakub Kicinski Signed-off-by: Jiong Wang Signed-off-by: Alexei Starovoitov --- drivers/net/ethernet/netronome/nfp/bpf/jit.c | 30 ++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c index aa3a2098a583..093b8ff80241 100644 --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c @@ -1967,6 +1967,9 @@ static int neg_reg64(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta) */ static int __shl_imm64(struct nfp_prog *nfp_prog, u8 dst, u8 shift_amt) { + if (!shift_amt) + return 0; + if (shift_amt < 32) { emit_shf(nfp_prog, reg_both(dst + 1), reg_a(dst + 1), SHF_OP_NONE, reg_b(dst), SHF_SC_R_DSHF, @@ -2079,6 +2082,9 @@ static int shl_reg64(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta) */ static int __shr_imm64(struct nfp_prog *nfp_prog, u8 dst, u8 shift_amt) { + if (!shift_amt) + return 0; + if (shift_amt < 32) { emit_shf(nfp_prog, reg_both(dst), reg_a(dst + 1), SHF_OP_NONE, reg_b(dst), SHF_SC_R_DSHF, shift_amt); @@ -2180,6 +2186,9 @@ static int shr_reg64(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta) */ static int __ashr_imm64(struct nfp_prog *nfp_prog, u8 dst, u8 shift_amt) { + if (!shift_amt) + return 0; + if (shift_amt < 32) { emit_shf(nfp_prog, reg_both(dst), reg_a(dst + 1), SHF_OP_NONE, reg_b(dst), SHF_SC_R_DSHF, shift_amt); @@ -2388,10 +2397,13 @@ static int neg_reg(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta) static int __ashr_imm(struct nfp_prog *nfp_prog, u8 dst, u8 shift_amt) { - /* Set signedness bit (MSB of result). */ - emit_alu(nfp_prog, reg_none(), reg_a(dst), ALU_OP_OR, reg_imm(0)); - emit_shf(nfp_prog, reg_both(dst), reg_none(), SHF_OP_ASHR, reg_b(dst), - SHF_SC_R_SHF, shift_amt); + if (shift_amt) { + /* Set signedness bit (MSB of result). */ + emit_alu(nfp_prog, reg_none(), reg_a(dst), ALU_OP_OR, + reg_imm(0)); + emit_shf(nfp_prog, reg_both(dst), reg_none(), SHF_OP_ASHR, + reg_b(dst), SHF_SC_R_SHF, shift_amt); + } wrp_immed(nfp_prog, reg_both(dst + 1), 0); return 0; @@ -2433,12 +2445,10 @@ static int shl_imm(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta) { const struct bpf_insn *insn = &meta->insn; - if (!insn->imm) - return 1; /* TODO: zero shift means indirect */ - - emit_shf(nfp_prog, reg_both(insn->dst_reg * 2), - reg_none(), SHF_OP_NONE, reg_b(insn->dst_reg * 2), - SHF_SC_L_SHF, insn->imm); + if (insn->imm) + emit_shf(nfp_prog, reg_both(insn->dst_reg * 2), + reg_none(), SHF_OP_NONE, reg_b(insn->dst_reg * 2), + SHF_SC_L_SHF, insn->imm); wrp_immed(nfp_prog, reg_both(insn->dst_reg * 2 + 1), 0); return 0; -- cgit v1.2.3