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epc status cause all are reported zero?

To: linux-mips@linux-mips.org
Subject: epc status cause all are reported zero?
From: "atul srivastava" <atulsrivastava9@rediffmail.com>
Date: 20 Nov 2002 10:46:38 -0000
Original-recipient: rfc822;linux-mips@linux-mips.org
Reply-to: "atul srivastava" <atulsrivastava9@rediffmail.com>
Sender: linux-mips-bounce@linux-mips.org
Hello all,

I have a wiered problem.

following is the Oops by kernel when it tries to exec the shell.

while loading /bin/sh it reads the elf_ex.e_entry as 0x4000b0 this address is confirmed by
mip-linux-objdump -S bin/sh after mount -o loop on my host.
$mips-linux-objdump -S ./sh

./sh:     file format elf32-bigmips

Disassembly of section .text:

00000000004000b0 <.text>:
  4000b0:       3c1c0fc1        lui     $gp,0xfc1
  4000b4:       279c96e0        addiu   $gp,$gp,-26912
  4000b8:       0399e021        addu    $gp,$gp,$t9


During exec there is a page fault of 4000b0 but immediately after that i get another page fault 0f 0x0fc01788 and following register dump after it
fails to get a fixup address.

Unable to handle kernel paging request at virtual address 0fc01788, epc == 00000Oops in fault.c:do_page_fault, line 230:
$0 : 00000000 00000000 00000000 00000000
$4 : 00007340 800f0474 00000000 801fa000
$8 : 00000000 00000000 00000000 4c696e75
$12: 78000000 00000000 00000000 00000000
$16: 00000000 00000000 00000000 00000000
$20: 00000000 00000000 00000000 00000000
$24: 00000000 00000000
$28: 6e652900 00000000 00000000 00000000
epc   : 00000000
Status: 00000000
Cause : 00000000
Process sh (pid: 1, stackpage=801fa000)


i am confused how come the epc status and cause register all are reported zero. whether my regs ( pointer to struct pt_regs) is pointing somewhere else..?

secondly Is this a problem with shell or kernel..? may be somewhere the kernel is not checking the
validity of user space address and hence this problem..

to avoid any other posibilities i am running uncached.

any thought

Best Regards,
Atul



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