From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: laniel_francis@privacyrequired.com,
linux-efi <linux-efi@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v1 07/12] efi: Replace strstarts() by str_has_prefix().
Date: Sat, 05 Dec 2020 12:24:10 -0800 [thread overview]
Message-ID: <3161fc13d69c388b1f51f59c6ecea48dcd0a7856.camel@HansenPartnership.com> (raw)
In-Reply-To: <CAMj1kXFvCZKH-Bbvu-V5-GxcTun8yz98igeFxRc1tTswbttM0w@mail.gmail.com>
On Sat, 2020-12-05 at 20:36 +0100, Ard Biesheuvel wrote:
> On Fri, 4 Dec 2020 at 19:02, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > On Fri, 2020-12-04 at 18:07 +0100, Ard Biesheuvel wrote:
> > > On Fri, 4 Dec 2020 at 18:06, <laniel_francis@privacyrequired.com>
> > > wrote:
> > > > From: Francis Laniel <laniel_francis@privacyrequired.com>
> > > >
> > > > The two functions indicates if a string begins with a given
> > > > prefix. The only difference is that strstarts() returns a bool
> > > > while str_has_prefix() returns the length of the prefix if the
> > > > string begins with it or 0 otherwise.
> > > >
> > >
> > > Why?
> >
> > I think I can answer that. If the conversion were done properly
> > (which it's not) you could get rid of the double strings in the
> > code which are error prone if you update one and forget
> > another. This gives a good example: 3d739c1f6156 ("tracing: Use
> > the return of str_has_prefix() to remove open coded numbers"). so
> > in your code you'd replace things like
> >
> > if (strstarts(option, "rgb")) {
> > option += strlen("rgb");
> > ...
> >
> > with
> >
> > len = str_has_prefix(option, "rgb");
> > if (len) {
> > option += len
> > ...
> >
> > Obviously you also have cases where strstart is used as a boolean
> > with no need to know the length ... I think there's no value to
> > converting those.
> >
>
> This will lead to worse code being generated. strlen() is evaluated
> at build time by the compiler if the argument is a string literal, so
> your 'before' version gets turned into 'option += 3', whereas the
> latter needs to use a runtime variable.
str_has_prefix() is an always_inline function so it should be build
time evaluated as well. I think most compilers see len as being a
constant and unchanged, so elide the variable. This means the code
generated should be the same.
> So I don't object to using str_has_prefix() in new code in this way,
> but I really don't see the point of touching existing code.
That's your prerogative as a Maintainer ... I was just explaining what
the original author had in mind when str_has_prefix() was created.
James
next prev parent reply other threads:[~2020-12-05 20:24 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-04 17:03 [RFC PATCH v1 00/12] Replace strstarts() by str_has_prefix() laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 01/12] arm: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 02/12] mips: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 03/12] crypto: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 04/12] device-mapper: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 05/12] renesas: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 06/12] omap: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 07/12] efi: " laniel_francis
2020-12-04 17:07 ` Ard Biesheuvel
2020-12-04 17:19 ` Francis Laniel
2020-12-04 18:02 ` James Bottomley
2020-12-05 19:08 ` Francis Laniel
2020-12-05 19:36 ` Ard Biesheuvel
2020-12-05 20:24 ` James Bottomley [this message]
2020-12-05 20:57 ` Ard Biesheuvel
2020-12-05 21:15 ` James Bottomley
2020-12-05 21:20 ` Ard Biesheuvel
2020-12-05 23:04 ` James Bottomley
2020-12-07 15:10 ` Steven Rostedt
2020-12-07 16:25 ` David Laight
2020-12-05 20:28 ` Rasmus Villemoes
2020-12-10 18:14 ` Arvind Sankar
2020-12-11 9:45 ` David Laight
2020-12-11 16:10 ` Arvind Sankar
2020-12-04 17:03 ` [RFC PATCH v1 08/12] ide: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 09/12] mips: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 10/12] module: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 11/12] musb: " laniel_francis
2020-12-04 17:03 ` [RFC PATCH v1 12/12] string.h: Remove strstarts() laniel_francis
2020-12-04 17:56 ` [RFC PATCH v1 00/12] Replace strstarts() by str_has_prefix() James Bottomley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3161fc13d69c388b1f51f59c6ecea48dcd0a7856.camel@HansenPartnership.com \
--to=james.bottomley@hansenpartnership.com \
--cc=ardb@kernel.org \
--cc=laniel_francis@privacyrequired.com \
--cc=linux-efi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).