linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ard Biesheuvel <ardb@kernel.org>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
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, 5 Dec 2020 20:36:02 +0100	[thread overview]
Message-ID: <CAMj1kXFvCZKH-Bbvu-V5-GxcTun8yz98igeFxRc1tTswbttM0w@mail.gmail.com> (raw)
In-Reply-To: <ab769a5188394cd3379cc627d14a0222050a1367.camel@HansenPartnership.com>

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.

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.

  parent reply	other threads:[~2020-12-05 19:37 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-04 17:03 [RFC PATCH v1 00/12] " 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 [this message]
2020-12-05 20:24         ` James Bottomley
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=CAMj1kXFvCZKH-Bbvu-V5-GxcTun8yz98igeFxRc1tTswbttM0w@mail.gmail.com \
    --to=ardb@kernel.org \
    --cc=James.Bottomley@hansenpartnership.com \
    --cc=laniel_francis@privacyrequired.com \
    --cc=linux-efi@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --subject='Re: [RFC PATCH v1 07/12] efi: Replace strstarts() by str_has_prefix().' \
    /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

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).