netdev - Re: [PATCH bpf-next v9 02/11] bpf: use last 8-bits for the nr

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Message-ID: <20260114095221.460c059b@pumpkin>
Date: Wed, 14 Jan 2026 09:52:21 +0000
From: David Laight <david.laight.linux@...il.com>
To: Menglong Dong <menglong.dong@...ux.dev>
Cc: Menglong Dong <menglong8.dong@...il.com>, Andrii Nakryiko
 <andrii.nakryiko@...il.com>, ast@...nel.org, andrii@...nel.org,
 daniel@...earbox.net, martin.lau@...ux.dev, eddyz87@...il.com,
 song@...nel.org, yonghong.song@...ux.dev, john.fastabend@...il.com,
 kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
 davem@...emloft.net, dsahern@...nel.org, tglx@...utronix.de,
 mingo@...hat.com, jiang.biao@...ux.dev, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 bpf@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v9 02/11] bpf: use last 8-bits for the nr_args
 in trampoline

On Wed, 14 Jan 2026 10:19:02 +0800
Menglong Dong <menglong.dong@...ux.dev> wrote:

> On 2026/1/14 09:22 Andrii Nakryiko <andrii.nakryiko@...il.com> write:
> > On Sat, Jan 10, 2026 at 6:11 AM Menglong Dong <menglong8.dong@...il.com> wrote:  
> > >
> > > For now, ctx[-1] is used to store the nr_args in the trampoline. However,
> > > 1-byte is enough to store such information. Therefore, we use only the
> > > last byte of ctx[-1] to store the nr_args, and reserve the rest for other  
> > 
> > Looking at the assembly below I think you are extracting the least
> > significant byte, right? I'd definitely not call it "last" byte...
> > Let's be precise and unambiguous here.  
> 
> Yeah, the "last 8-bits", "last byte" is ambiguous. So let's describe it as
> "the least significant byte" here instead :)

Or just s/last/low/

	David

> 
> Thanks!
> Menglong Dong