Re: [PATCH] MIPS: Display CPU byteorder in /proc/cpuinfo

[Antony Pavlov <antonynpavlov@gmail.com>]

On Tue, 20 Jan 2015 15:05:32 -0800
David Daney <ddaney.cavm@gmail.com> wrote:

> On 01/19/2015 01:02 AM, Joshua Kinard wrote:
> > From: Joshua Kinard <kumba@gentoo.org>
> >
> > This is a small patch to display the CPU byteorder that the kernel was compiled
> > with in /proc/cpuinfo.
> 
> What would use this?  Or in other words, why is this needed?

If you run some test software (e.g. in particular benchmarking software)
on a linux system then you are interisting in a log file with system information.
It's very likely that your log file keeps /proc/cpuinfo content.
So if your /proc/cpuinfo has byteorder information then your have system
byteorder information in your log file for free :)

If you write a bugreport and your attach /proc/cpuinfo content to it
then a bugreport reader have no question on byteorder.

> 
> Userspace C code doesn't need this as it has its own standard ways of 
> determining endianness.
> 
> If you need to know as a user you can do:
> 
>     readelf -h /bin/sh | grep Data | cut -d, -f2

Does this line really show your current CPU byteorder?

IMHO this 'readelf' method is not very reliable :)

> 
> 
> >
> > Signed-off-by: Joshua Kinard <kumba@gentoo.org>
> > ---
> >   arch/mips/kernel/proc.c |    5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > This patch has been submitted several times prior over the years (I think), but
> > I don't recall what, if any, objections there were to it.
> >
> > linux-mips-proc-cpuinfo-byteorder.patch
> > diff --git a/arch/mips/kernel/proc.c b/arch/mips/kernel/proc.c
> > index 097fc8d..75e6a62 100644
> > --- a/arch/mips/kernel/proc.c
> > +++ b/arch/mips/kernel/proc.c
> > @@ -65,6 +65,11 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> >   	seq_printf(m, "BogoMIPS\t\t: %u.%02u\n",
> >   		      cpu_data[n].udelay_val / (500000/HZ),
> >   		      (cpu_data[n].udelay_val / (5000/HZ)) % 100);
> > +#ifdef __MIPSEB__
> > +	seq_printf(m, "byteorder\t\t: big endian\n");
> > +#else
> > +	seq_printf(m, "byteorder\t\t: little endian\n");
> > +#endif
> >   	seq_printf(m, "wait instruction\t: %s\n", cpu_wait ? "yes" : "no");
> >   	seq_printf(m, "microsecond timers\t: %s\n",
> >   		      cpu_has_counter ? "yes" : "no");
> >
> >
> >
> 
> 


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Best regards,
  Antony Pavlov