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Re: page size change on MIPS

To: naveen yadav <yad.naveen@gmail.com>
Subject: Re: page size change on MIPS
From: David Daney <ddaney@caviumnetworks.com>
Date: Fri, 28 Jan 2011 10:48:58 -0800
Cc: adnan iqbal <adnan.iqbal@seecs.edu.pk>, linux-mips@linux-mips.org, kernelnewbies@nl.linux.org
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On 01/28/2011 01:18 AM, naveen yadav wrote:
Hi all

I try changing the kernel_execve() function as suggested, but it fails,
I am using code sourcery toolchain 4.4.1 but it still fails. I am
using 2.6.30.9 kernel and this function is part of it.



Quit trying to change kernel_execve().  It is perfect as it is.

The problem is elsewhere.



Kind regards


Thank you.


On Thu, Jan 27, 2011 at 11:14 PM, David Daney<ddaney@caviumnetworks.com>  wrote:
On 01/27/2011 07:18 AM, adnan iqbal wrote:

Please try this. One line of code is added ( move    %1, $7).


int kernel_execve(const char *filename, char *const argv[], char *const
envp[])
{
        register unsigned long __a0 asm("$4") = (unsigned long) filename;
        register unsigned long __a1 asm("$5") = (unsigned long) argv;
        register unsigned long __a2 asm("$6") = (unsigned long) envp;
        register unsigned long __a3 asm("$7");
        unsigned long __v0;
        __asm__ volatile ("                                     \n"
        "       .set    noreorder                               \n"
        "       li      $2, %5          # __NR_execve           \n"
        "       syscall                                         \n"
        "       move    %0, $2                                  \n"
     "      move    %1, $7                    \n"
        "       .set    reorder                                 \n"
        : "=&r" (__v0), "=r" (__a3)
        : "r" (__a0), "r" (__a1), "r" (__a2), "i" (__NR_execve)
        : "$2", "$8", "$9", "$10", "$11", "$12", "$13", "$14", "$15",
"$24",
          "memory");


        if (__a3 == 0)
                return __v0;
        return -__v0;
}


I don't know where you got that code.  But really you should do what glibc
does.  glibc gets it correct.

At a minimum you are missing "hi" and "lo" clobbers.

Ignore that ^^^^^ advice.


If the code works with 16K pages, and not 64K pages, then this snippet is
not the problem.  Likely your problem is the layout of the PHDRs in the
executable is not compatible with the page size.


Instead look at this issue.

David Daney



On Thu, Jan 27, 2011 at 7:55 PM, naveen yadav<yad.naveen@gmail.com>
  wrote:

Hi David,

thanks for your response.

I check and found that kernel is booting with 16KB page size with
ramdisk booting. But when I change to 64KB it give me

: applet not found
                  Kernel panic - not syncing: Attempted to kill init!
so I check and found that it is not able to execute well the system
call in kernel_execve function.
I am using codesourcercy toolchain(4.3.1). So is there a way to debug
this problem or how to debug below function.

int kernel_execve(const char *filename, char *const argv[], char *const
envp[])
{
        register unsigned long __a0 asm("$4") = (unsigned long) filename;
        register unsigned long __a1 asm("$5") = (unsigned long) argv;
        register unsigned long __a2 asm("$6") = (unsigned long) envp;
        register unsigned long __a3 asm("$7");
        unsigned long __v0;
        __asm__ volatile ("                                     \n"
        "       .set    noreorder                               \n"
        "       li      $2, %5          # __NR_execve           \n"
        "       syscall                                         \n"
        "       move    %0, $2                                  \n"
        "       .set    reorder                                 \n"
        : "=&r" (__v0), "=r" (__a3)
        : "r" (__a0), "r" (__a1), "r" (__a2), "i" (__NR_execve)
        : "$2", "$8", "$9", "$10", "$11", "$12", "$13", "$14", "$15",
"$24",
          "memory");


        if (__a3 == 0)
                return __v0;
        return -__v0;
}


On Tue, Jan 25, 2011 at 12:26 AM, David Daney<ddaney@caviumnetworks.com>
wrote:

On 01/24/2011 07:02 AM, naveen yadav wrote:

Hi All,


we are using mips32r2  so I want to know which all pages size it can
support?
When I modify arch/mips/Kconfig.  it boot sucessfully on 16KB page
size. but hang/not boot crash when change page size to 8KB,32KB and 64
KB.

I don't think 8KB and 32KB work on most mips32r2 processors.  You would

have

to check the processor manual to be sure.



We are using 2.6.30 kernel.

At Page Size 8KB and 32KB  it hang in unpack_to_rootfs() function of
init/initramfs.c

64KB it hangs when execute init  Kernel panic - not syncing: Attempted
to kill init!

I regularly run 4K, 16K, and 64K page sizes with a Debian rootfs.  If
you
run with a broken uClibc toolchain that doesn't support larger pages, it
will of course fail.  In this case the problem is with your toolchain,

not

the kernel.

David Daney



config PAGE_SIZE_4KB
         bool "4kB"
         help
          This option select the standard 4kB Linux page size.  On some
          R3000-family processors this is the only available page size.
  Using
          4kB page size will minimize memory consumption and is
therefore
          recommended for low memory systems.

config PAGE_SIZE_8KB
         bool "8kB"
        depends on (EXPERIMENTAL&&     CPU_R8000) || CPU_CAVIUM_OCTEON
         help
           Using 8kB page size will result in higher performance kernel

at

           the price of higher memory consumption.  This option is
available
           only on R8000 and cnMIPS processors.  Note that you will need

a

           suitable Linux distribution to support this.

config PAGE_SIZE_16KB
         bool "16kB"
        depends on !CPU_R3000&&     !CPU_TX39XX
         help
           Using 16kB page size will result in higher performance kernel

at

           the price of higher memory consumption.  This option is
available on
           all non-R3000 family processors.  Note that you will need a
suitable
           Linux distribution to support this.

config PAGE_SIZE_32KB
         bool "32kB"
         help
           Using 32kB page size will result in higher performance kernel

at

           the price of higher memory consumption.  This option is
available
           only on cnMIPS cores.  Note that you will need a suitable

Linux

           distribution to support this.

config PAGE_SIZE_64KB
         bool "64kB"
        depends on EXPERIMENTAL&&     !CPU_R3000&&     !CPU_TX39XX
         help
           Using 64kB page size will result in higher performance kernel

at

           the price of higher memory consumption.  This option is
available on
           all non-R3000 family processor.  Not that at the time of this
           writing this option is still high experimental.












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