From: Will Deacon <will.deacon@arm.com>
To: Z Lim <zlim.lnx@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Catalin Marinas <catalin.marinas@arm.com>,
Yang Shi <yang.shi@linaro.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Network Development <netdev@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net-next 2/3] arm64: bpf: optimize JMP_CALL
Date: Tue, 7 Jun 2016 09:10:43 +0100 [thread overview]
Message-ID: <20160607081042.GA9951@arm.com> (raw)
In-Reply-To: <CABg9mcvXxAvWxuXJbBbQEy5_nsgPjT6Y20CFNKMkOYJp4NrnFQ@mail.gmail.com>
On Mon, Jun 06, 2016 at 09:36:03PM -0700, Z Lim wrote:
> On Mon, Jun 6, 2016 at 10:05 AM, Will Deacon <will.deacon@arm.com> 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 <zlim.lnx@gmail.com>
> >> ---
> >> 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
next prev parent reply other threads:[~2016-06-07 8:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-04 22:00 [PATCH net-next 1/3] arm64: bpf: implement bpf_tail_call() helper Zi Shen Lim
2016-06-04 22:00 ` [PATCH net-next 2/3] arm64: bpf: optimize JMP_CALL Zi Shen Lim
2016-06-06 17:05 ` Will Deacon
2016-06-07 4:36 ` Z Lim
2016-06-07 8:10 ` Will Deacon [this message]
2016-06-04 22:00 ` [PATCH net-next 3/3] arm64: bpf: optimize LD_ABS, LD_IND Zi Shen Lim
2016-06-04 23:46 ` [PATCH net-next 1/3] arm64: bpf: implement bpf_tail_call() helper kbuild test robot
2016-06-05 7:53 ` Daniel Borkmann
2016-06-06 4:56 ` Z Lim
2016-06-06 8:11 ` Daniel Borkmann
2016-06-07 2:33 ` Zi Shen Lim
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