From: Yonghong Song <yonghong.song@linux.dev>
To: dthaler1968@googlemail.com, bpf@ietf.org, bpf@vger.kernel.org
Subject: Re: Sign extension ISA question
Date: Tue, 16 Jan 2024 14:34:41 -0800 [thread overview]
Message-ID: <829aa552-b04e-4f08-9874-b3f929741852@linux.dev> (raw)
In-Reply-To: <08ab01da48be$603541a0$209fc4e0$@gmail.com>
On 1/16/24 12:55 PM, dthaler1968@googlemail.com wrote:
> (Resending since a spam filter seems to have blocked the first attempt.)
>
> Is there any semantic difference between the following two instructions?
>
> {.opcode = BPF_ALU64 | BPF_MOV | BPF_K, .offset = 0, .imm = -1}
This is supported. Sign extension of -1 will be put into ALU64 reg.
>
> {.opcode = BPF_ALU64 | BPF_MOVSX | BPF_K, .offset = 32, .imm = -1}
This is not supported. BPF_MOVSX only supports register extension.
We should make it clear in the doc.
>
> From my reading both of them treat imm as a signed 32-bit number and
> sign-extend it to 64 bits.
>
> Dave
>
>
WARNING: multiple messages have this Message-ID (diff)
From: Yonghong Song <yonghong.song@linux.dev>
To: dthaler1968@googlemail.com, bpf@ietf.org, bpf@vger.kernel.org
Subject: Re: [Bpf] Sign extension ISA question
Date: Tue, 16 Jan 2024 14:34:41 -0800 [thread overview]
Message-ID: <829aa552-b04e-4f08-9874-b3f929741852@linux.dev> (raw)
Message-ID: <20240116223441.Lik407Qog773W5MWn9IXIyB4k_hpO6f1q5KIM0Xo0-8@z> (raw)
In-Reply-To: <08ab01da48be$603541a0$209fc4e0$@gmail.com>
On 1/16/24 12:55 PM, dthaler1968@googlemail.com wrote:
> (Resending since a spam filter seems to have blocked the first attempt.)
>
> Is there any semantic difference between the following two instructions?
>
> {.opcode = BPF_ALU64 | BPF_MOV | BPF_K, .offset = 0, .imm = -1}
This is supported. Sign extension of -1 will be put into ALU64 reg.
>
> {.opcode = BPF_ALU64 | BPF_MOVSX | BPF_K, .offset = 32, .imm = -1}
This is not supported. BPF_MOVSX only supports register extension.
We should make it clear in the doc.
>
> From my reading both of them treat imm as a signed 32-bit number and
> sign-extend it to 64 bits.
>
> Dave
>
>
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next prev parent reply other threads:[~2024-01-16 22:34 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-16 20:38 [Bpf] Sign extension ISA question dthaler1968=40googlemail.com
2024-01-16 20:55 ` dthaler1968
2024-01-16 20:55 ` [Bpf] " dthaler1968=40googlemail.com
2024-01-16 22:34 ` Yonghong Song [this message]
2024-01-16 22:34 ` Yonghong Song
2024-01-17 1:56 ` dthaler1968
2024-01-17 1:56 ` [Bpf] " dthaler1968=40googlemail.com
2024-01-17 3:48 ` Yonghong Song
2024-01-17 3:48 ` [Bpf] " Yonghong Song
2024-01-24 2:07 ` Jump instructions clarification dthaler1968
2024-01-24 2:07 ` [Bpf] " dthaler1968=40googlemail.com
2024-01-24 19:33 ` Yonghong Song
2024-01-24 19:33 ` [Bpf] " Yonghong Song
2024-01-26 1:12 ` 64-bit immediate " dthaler1968
2024-01-26 1:12 ` [Bpf] " dthaler1968=40googlemail.com
2024-01-26 5:34 ` Yonghong Song
2024-01-26 5:34 ` [Bpf] " Yonghong Song
2024-01-26 22:27 ` dthaler1968
2024-01-26 22:27 ` [Bpf] " dthaler1968=40googlemail.com
2024-01-27 3:41 ` Yonghong Song
2024-01-27 3:41 ` [Bpf] " Yonghong Song
2024-01-27 6:56 ` dthaler1968
2024-01-27 6:56 ` [Bpf] " dthaler1968=40googlemail.com
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