From: Z Lim <zlim.lnx@gmail.com>
To: Will Deacon <will.deacon@arm.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: Mon, 6 Jun 2016 21:36:03 -0700 [thread overview]
Message-ID: <CABg9mcvXxAvWxuXJbBbQEy5_nsgPjT6Y20CFNKMkOYJp4NrnFQ@mail.gmail.com> (raw)
In-Reply-To: <20160606170515.GK669@arm.com>
Hi Will,
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.
>
> Will
next prev parent reply other threads:[~2016-06-07 4:36 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 [this message]
2016-06-07 8:10 ` Will Deacon
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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