linux-kernel - Re: [PATCH] staging: rtl8723bs: Replace `& 0xfff` with `% 4096u`

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Message-ID: <209e5330-a4d4-4ecc-8d56-199f4a190c3c@stanley.mountain>
Date: Sat, 12 Apr 2025 17:19:12 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Abraham Samuel Adekunle <abrahamadekunle50@...il.com>,
	outreachy@...ts.linux.dev, julia.lawall@...ia.fr,
	gregkh@...uxfoundation.org, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org, david.laight.linux@...il.com,
	andy@...nel.org
Subject: Re: [PATCH] staging: rtl8723bs: Replace `& 0xfff` with `% 4096u`

On Fri, Apr 11, 2025 at 03:47:40PM +0300, Andy Shevchenko wrote:
> On Fri, Apr 11, 2025 at 1:37 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > On Thu, Apr 10, 2025 at 08:43:53PM +0300, Andy Shevchenko wrote:
> > >
> > > > $ make drivers/staging/rtl8723bs/core/rtw_xmit.o
> > > > $ cmp rtw_xmit_before.o rtw_xmit_after.o
> > >
> > > cmp is good but not good enough in general. Here it shows the 1:1
> > > binary, but in some cases code can be the same, while binaries are
> > > different. To make sure the code is the same use the bloat-o-meter
> > > tool instead.
> >
> > I don't understand what you're saying at all.  cmp shows that the compiler
> > was automaticall tanslating the "& 0xfff" into "% 04096u" so the resulting
> > object files are exactly the same.
> 
> There is a possibility that the compiler changes the code to the
> equivalent and cmp will break, bloat-o-meter will check at least what
> happened to the size of the *code*. object file is not only a code. It
> may also contain debug symbols and other stuff which may break cmp,
> while the code can be *the same*.

So far as I can see bloat-o-meter is only looking at the size.  I
deliberately introduced a bug to see if bloat-o-meter said anything but
it said the size was the same.

regards,
dan carpenter