From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Tue, 7 Jun 2016 09:10:43 +0100 Subject: [PATCH net-next 2/3] arm64: bpf: optimize JMP_CALL In-Reply-To: References: <1465077630-633-1-git-send-email-zlim.lnx@gmail.com> <1465077630-633-2-git-send-email-zlim.lnx@gmail.com> <20160606170515.GK669@arm.com> Message-ID: <20160607081042.GA9951@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jun 06, 2016 at 09:36:03PM -0700, Z Lim wrote: > On Mon, Jun 6, 2016 at 10:05 AM, Will Deacon wrote: > > On Sat, Jun 04, 2016 at 03:00:29PM -0700, Zi Shen Lim wrote: > >> Remove superfluous stack frame, saving us 3 instructions for > >> every JMP_CALL. > >> > >> Signed-off-by: Zi Shen Lim > >> --- > >> arch/arm64/net/bpf_jit_comp.c | 3 --- > >> 1 file changed, 3 deletions(-) > >> > >> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c > >> index 51abc97..7ae304e 100644 > >> --- a/arch/arm64/net/bpf_jit_comp.c > >> +++ b/arch/arm64/net/bpf_jit_comp.c > >> @@ -578,11 +578,8 @@ emit_cond_jmp: > >> const u64 func = (u64)__bpf_call_base + imm; > >> > >> emit_a64_mov_i64(tmp, func, ctx); > >> - emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); > >> - emit(A64_MOV(1, A64_FP, A64_SP), ctx); > >> emit(A64_BLR(tmp), ctx); > >> emit(A64_MOV(1, r0, A64_R(0)), ctx); > >> - emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); > >> break; > >> } > > > > Is the jitted code intended to be unwindable by standard tools? > > Before this patch: > bpf_prologue => push stack frame > ... > jmp_call => push stack frame, call bpf_helper*, pop stack frame > ... > bpf_epilogue => pop stack frame, ret > > Now: > bpf_prologue => push stack frame > ... > jmp_call => call bpf_helper* > ... > bpf_epilogue => pop stack frame, ret > > *Note: bpf_helpers in kernel/bpf/helper.c > > So yes, it's still unwindable. Sure, I'm not disputing that. I just wondered whether or not it needs to be unwindable at all... Will