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Message-ID: <mb61po7if3b0w.fsf@amazon.com>
Date: Wed, 06 Sep 2023 09:29:19 +0000
From: Puranjay Mohan <puranjay12@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Shubham Bansal <illusionist.neo@...il.com>,
Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 6/8] arm32, bpf: add support for 64 bit
division instruction
On Tue, Sep 05 2023, Russell King (Oracle) wrote:
> On Tue, Sep 05, 2023 at 09:06:19PM +0000, Puranjay Mohan wrote:
>> +cont:
>> +
>> + /* Call appropriate function */
>> + if (sign)
>> + emit_mov_i(ARM_IP, op == BPF_DIV ? (u32)jit_sdiv64 : (u32)jit_smod64, ctx);
>> + else
>> + emit_mov_i(ARM_IP, op == BPF_DIV ? (u32)jit_udiv64 : (u32)jit_mod64, ctx);
>
> Same comment as the previous patch here.
Will fix both in next version.
>
>> +
>> + emit_blx_r(ARM_IP, ctx);
>> +
>> + /* Save return value */
>> + if (rd[1] != ARM_R0) {
>> + emit(ARM_MOV_R(rd[0], ARM_R1), ctx);
>> + emit(ARM_MOV_R(rd[1], ARM_R0), ctx);
>> + }
>> +
>> + /* Recover {R1, R0} from stack if it is not Rd */
>> + if (rd[1] != ARM_R0)
>> + emit(ARM_POP(BIT(ARM_R0) | BIT(ARM_R1)), ctx);
>> + else
>> + emit(ARM_ADD_I(ARM_SP, ARM_SP, 8), ctx);
>> +
>> + /* Recover {R3, R2} from stack if it is not Rd */
>> + if (rd[1] != ARM_R2)
>> + emit(ARM_POP(BIT(ARM_R2) | BIT(ARM_R3)), ctx);
>> + else
>> + emit(ARM_ADD_I(ARM_SP, ARM_SP, 8), ctx);
>
> if (rd[1] != ARM_R0) {
> emit(ARM_POP(BIT(ARM_R0) | BIT(ARM_R1)), ctx);
> emit(ARM_ADD_I(ARM_SP, ARM_SP, 8), ctx);
> } else if (rd[1] != ARM_R2) {
> emit(ARM_ADD_I(ARM_SP, ARM_SP, 8), ctx);
> emit(ARM_POP(BIT(ARM_R2) | BIT(ARM_R3)), ctx);
> } else {
> emit(ARM_ADD_I(ARM_SP, ARM_SP, 16), ctx);
> }
>
> Hmm?
Actually, there can also be a situation where rd[1] != ARM_R0 && rd[1] != ARM_R2,
so should I do it like:
if (rd[1] != ARM_R0 && rd[1] != ARM_R2) {
emit(ARM_POP(BIT(ARM_R0) | BIT(ARM_R1)), ctx);
emit(ARM_POP(BIT(ARM_R2) | BIT(ARM_R3)), ctx);
} else if (rd[1] != ARM_R0) {
emit(ARM_POP(BIT(ARM_R0) | BIT(ARM_R1)), ctx);
emit(ARM_ADD_I(ARM_SP, ARM_SP, 8), ctx);
} else if (rd[1] != ARM_R2) {
emit(ARM_ADD_I(ARM_SP, ARM_SP, 8), ctx);
emit(ARM_POP(BIT(ARM_R2) | BIT(ARM_R3)), ctx);
} else {
emit(ARM_ADD_I(ARM_SP, ARM_SP, 16), ctx);
}
Thanks,
Puranjay
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