vmcore file 0 size in x86_64

Thu Aug 13 08:45:54 EDT 2009

Hi,

I checked.. through and fond out that one of the following check condition 
is failing

 516         if (memcmp(ehdr.e_ident, ELFMAG, SELFMAG) != 0 ||
    517                 (ehdr.e_type != ET_CORE) ||
    518                 !vmcore_elf_check_arch(&ehdr) ||
    519                 ehdr.e_ident[EI_CLASS] != ELFCLASS64 ||
    520                 ehdr.e_ident[EI_VERSION] != EV_CURRENT ||
    521                 ehdr.e_version != EV_CURRENT ||
    522                 ehdr.e_ehsize != sizeof(Elf64_Ehdr) ||
    523                 ehdr.e_phentsize != sizeof(Elf64_Phdr) ||
    524                 ehdr.e_phnum == 0) {
    525                 printk(KERN_WARNING "Warning: Core image elf 
header is not"
    526 "sane:%ld\n",elfcorehdr_addr);
    527               return -EINVAL
    528         }

If I comment this return at line 527, then the code flows through and the 
vmcore is getting generated. 

However, I am facing a new issue, my user space is 32 bit and the kernel 
is 64 bit. And I want to access the high memory (high_memory - 
BACK_UP_SIZE) area of the previous/primary kernel. Where some log data I 
had saved. The toral RAM is 8GB.

As the 32 bit pointers could not reach there... means simple file 
operations lseek() , read etc are not working.. to access some region 
around 8GB.

Can you please suggest me some way to reach that memory and read my raw 
data from the user space. 

I am able to read the data from kernel space( a simple kernel module via 
/proc interface to transfer the data from kernel to user space using 
physical address of the primary kernel).

Chandan Kumar
TCS Mumbai

Chandan12 K <chandan12.k at tcs.com> 
Sent by: kexec-bounces at lists.infradead.org
08/13/2009 03:40 PM

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Subject
vmcore file 0 size in x86_64

Hi, 

Adding boot logs 

NET: Registered protocol family 1 
audit: initializing netlink socket (disabled) 
type=2000 audit(1250069944.104:1): initialized 
VFS: Disk quotas dquot_6.5.1 
Dquot-cache hash table entries: 512 (order 0, 4096 bytes) 
Warning: Core image elf header is notsane 
Kdump: vmcore not initialized 
Registering unionfs 2.2-mm 
msgmni has been set to 90 
io scheduler noop registered 
io scheduler anticipatory registered

however, similar case has already been discussed in other mailing lists 
with vivek. The only difference is that, I am not using redhat system and 
dont have any user level kexel tools.   

https://lists.linux-foundation.org/pipermail/fastboot/2007-January/012572.html 

The kernel command line of capture kernel (kexe'ed kernel) : Kernel 
command line: root=/dev/nfs rw console=ttyS0,115200 ip=::::::dhcp 
selinux=0 noacpi maxcpus=1 memmap=exactmap memmap=640K at 0K 
memmap=64876K at 16384K elfcorehdr=81260K 

Command line for the Primary kernel : root=/dev/nfs rw 
console=ttyS0,115200 ip=::::::dhcp crashkernel=64M at 16M 

kexec command used : kexec -p bzImage --append="root=/dev/nfs rw 
console=ttyS0,115200 ip=::::::dhcp selinux=0 noacpi maxcpus=1" 

Kconfig options : 

CONFIG_CRASH_DUMP=y 
CONFIG_PHYSICAL_START=0x200000 
CONFIG_RELOCATABLE=y 
CONFIG_PHYSICAL_ALIGN=0x200000

Please suggest. 

Chandan 

Dave Anderson <anderson at redhat.com> 
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08/12/2009 07:39 PM 

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Re: [Crash-utility] vmcore file size 0 on x86_64

Forwarded to kexec list:

http://lists.infradead.org/pipermail/kexec/2009-August/003474.html

----- "Chandan12 K" <chandan12.k at tcs.com> wrote:

> Hi,
> 
> I am little new in this mailing list. I just wondered if anybody could
> help me regarding the vmcore file generation. I ran kexec on my x86_64
> machine, and the /proc/vmcore file is created with zero size.
> 
> However, even if I read the /dev/oldmem file, I am only able to read
> till 16M. I guess I am only able to read till the 'X', where X is
> crashkernel=Y at X.
> 
> Moreover, My machine seems to have 32 bit user space and ofcourse, 64
> bit kernel space.
> 
> Appreciate any response.
> 
> Chandan Kumar
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