From: Jiri Slaby <jslaby@suse.cz>
To: Arnaud POULIQUEN <arnaud.pouliquen@st.com>,
Joe Perches <joe@perches.com>, Ohad Ben-Cohen <ohad@wizery.com>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linux-remoteproc@vger.kernel.org,
Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Suman Anna <s-anna@ti.com>,
Fabien DESSENNE <fabien.dessenne@st.com>,
linux-stm32@st-md-mailman.stormreply.com,
xiang xiao <xiaoxiang781216@gmail.com>
Subject: Re: [PATCH v7 2/2] tty: add rpmsg driver
Date: Thu, 26 Mar 2020 13:31:44 +0100 [thread overview]
Message-ID: <7329d7bb-c9cd-8eb2-12c2-0b6d5cc2accf@suse.cz> (raw)
In-Reply-To: <54d9b379-ba51-b29c-db58-6e305773ee96@st.com>
On 26. 03. 20, 11:59, Arnaud POULIQUEN wrote:
>
>
> On 3/26/20 1:01 AM, Joe Perches wrote:
>> On Wed, 2020-03-25 at 14:31 +0100, Jiri Slaby wrote:
>>> The question was exactly about that: can a compiler optimize it to a
>>> bare number or will strlen call remain there?
>>
>> $ cat str.c
>> #include <string.h>
>>
>> int foo(void)
>> {
>> return strlen("abc");
>> }
>>
>> $ gcc -c -O2 str.c
>> $ objdump -d str.o
>> str.o: file format elf64-x86-64
>>
>>
>> Disassembly of section .text:
>>
>> 0000000000000000 <foo>:
>> 0: f3 0f 1e fa endbr64
>> 4: b8 03 00 00 00 mov $0x3,%eax
>> 9: c3 retq
>>
>>
> same result with arm gcc using -O1 or -Og:
>
> str.o: file format elf32-littlearm
>
>
> Disassembly of section .text:
>
> 00000000 <foo>:
> 0: e3a00003 mov r0, #3
> 4: e12fff1e bx lr
>
> So in conclusion replacing sizeof by srlen even if not optimized in -o0, right?
Right, gcc guys just confirmed, that it's constant-folded during parsing
already. I asked them as I tried to dump the tree.original and the
constant was already there.
So we are safe to use strlen, at least for gcc :P. Others should adapt
if they don't follow.
thanks,
--
js
suse labs
next prev parent reply other threads:[~2020-03-26 12:31 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-24 17:04 [PATCH v7 0/2] Add rpmsg tty driver Arnaud Pouliquen
2020-03-24 17:04 ` [PATCH v7 1/2] rpmsg: core: add API to get MTU Arnaud Pouliquen
2020-03-31 17:36 ` Mathieu Poirier
2020-04-01 6:28 ` Jiri Slaby
2020-04-01 6:29 ` Jiri Slaby
2020-04-01 11:34 ` Arnaud POULIQUEN
2020-03-24 17:04 ` [PATCH v7 2/2] tty: add rpmsg driver Arnaud Pouliquen
2020-03-24 17:18 ` Greg Kroah-Hartman
2020-03-25 11:34 ` Arnaud POULIQUEN
2020-03-24 17:23 ` Joe Perches
2020-03-25 11:36 ` Arnaud POULIQUEN
2020-03-24 17:44 ` Randy Dunlap
2020-03-25 8:10 ` Jiri Slaby
2020-03-25 11:39 ` Arnaud POULIQUEN
2020-03-24 20:52 ` Bjorn Andersson
2020-03-25 16:57 ` Arnaud POULIQUEN
2020-04-06 14:18 ` Arnaud POULIQUEN
2020-04-06 14:18 ` Arnaud POULIQUEN
2020-05-06 2:54 ` Bjorn Andersson
2020-05-06 10:21 ` Arnaud POULIQUEN
2020-03-25 8:45 ` Jiri Slaby
2020-03-25 13:15 ` Arnaud POULIQUEN
2020-03-25 13:31 ` Jiri Slaby
2020-03-26 0:01 ` Joe Perches
2020-03-26 6:38 ` Jiri Slaby
2020-03-26 10:59 ` Arnaud POULIQUEN
2020-03-26 12:31 ` Jiri Slaby [this message]
2020-03-26 11:40 ` Arnaud POULIQUEN
2020-03-26 11:45 ` Jiri Slaby
2020-04-01 18:06 ` Mathieu Poirier
2020-04-02 15:25 ` Arnaud POULIQUEN
2020-04-03 20:18 ` Mathieu Poirier
2020-07-15 16:06 ` [PATCH v7 0/2] Add rpmsg tty driver Arnaud POULIQUEN
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