Re: [PATCH v7 2/2] tty: add rpmsg driver

From: Arnaud POULIQUEN <arnaud.pouliquen@st.com>
To: Joe Perches <joe@perches.com>, Jiri Slaby <jslaby@suse.cz>,
	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 11:59:28 +0100	[thread overview]
Message-ID: <54d9b379-ba51-b29c-db58-6e305773ee96@st.com> (raw)
In-Reply-To: <f97d9dc54178e4344512bc7986265f101f4639c6.camel@perches.com>

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?

Thanks,
Arnaud