> Date: Thu, 17 Jan 2013 14:17:36 -0500
> From: anderson@redhat.com
> To: crash-utility@redhat.com
> Subject: Re: [Crash-utility] questions about crash utility

> The fact that crash gets as far as it does at least means that the
> ELF header you've created was deemed acceptable as an ARM vmcore.
> However, the error messages re: "cpu_present_mask indicates..." and
> "cannot determine base kernel version" indicate that the data
> that was read from the vmcore was clearly not the correct data.
>
> The "cpu_present_mask" value that it read contained too
> many bits -- presuming that the 32-bit ARM processor is
> still limited to only 4 cpus. (looks like upstream that
> CONFIG_NR_CPUS is still 2 in the arch/arm/configs files.)
>
> But more indicative of the wrong data being read is the second
> "cannot determine base kernel version" message, which was generated
> after it read the kernel's "init_uts_ns" uts_namespace structure.
> After reading it, it sees that the "release" string contains
> non-ASCII data, whereas it should contain the kernel version:
>
> crash> p init_uts_ns
> init_uts_ns = $3 = {
> kref = {
> refcount = {
> counter = 2
> }
> },
> name = {
> sysname = "Linux\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> nodename = "phenom-01.lab.bos.redhat.com\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> release = "2.6.32-313.el6.x86_64\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> version = "#1 SMP Thu Sep 27 16:25:19 EDT 2012\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> machine = "x86_64\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> domainname = "(none)\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"
> }
> }
> crash>
>
> So it appears that you're reading data from the wrong
> locations in the dumpfile. You should be able to verify
> that by bringing up the crash session with the --minimal
> flag like this:
>
> $ crash --minimal vmlinux vmcore
>
> That will bypass most of the initialization, including all
> readmem() calls of the vmcore. Then do this:
>
> crash> rd linux_banner 20
> ffffffff818000a0: 65762078756e694c 2e33206e6f697372 Linux version 3.
> ffffffff818000b0: 63662e312d312e35 365f3638782e3731 5.1-1.fc17.x86_6
> ffffffff818000c0: 626b636f6d282034 69756240646c6975 4 (mockbuild@bui
> ffffffff818000d0: 2e33322d6d76646c 6465662e32786870 ldvm-23.phx2.fed
> ffffffff818000e0: 656a6f727061726f 202967726f2e7463 oraproject.org)
> ffffffff818000f0: 7265762063636728 372e34206e6f6973 (gcc version 4.7
> ffffffff81800100: 303231303220302e 6465522820373035 .0 20120507 (Red
> ffffffff81800110: 372e342074614820 47282029352d302e Hat 4.7.0-5) (G
> ffffffff81800120: 3123202920294343 75685420504d5320 CC) ) #1 SMP Thu
> ffffffff81800130: 3120392067754120 2033343a30353a37 Aug 9 17:50:43
> crash> rd -a linux_banner
> ffffffff818000a0: Linux version 3.5.1-1.fc17.x86_64 (mockbuild@buildvm-23.phx2
> ffffffff818000dc: .fedoraproject.org) (gcc version 4.7.0 20120507 (Red Hat 4.7
> ffffffff81800118: .0-5) (GCC) ) #1 SMP Thu Aug 9 17:50:43 UTC 2012
> crash>
>
> I'm guessing that you will not see a string starting with "Linux version"
> with your dumpfile as shown above.
>
> If that's the case, then it's clear that the readmem() function is ultimately
> reading from the wrong vmcore file offset.
>
> Here's what you can try doing. Taking the linux_banner example above,
> you can check where in the dumpfile it's reading from by setting the debug
> flag, before doing a simple read -- like this example on an ARM dumpfile:
>
> crash> set debug 8
> debug: 8
> crash> rd linux_banner
> <addr: c033ea10 count: 1 flag: 488 (KVADDR)>
> <readmem: c033ea10, KVADDR, "32-bit KVADDR", 4, (FOE), ff94f048>
> <read_kdump: addr: c033ea10 paddr: 33ea10 cnt: 4>
> read_netdump: addr: c033ea10 paddr: 33ea10 cnt: 4 offset: 33f088
> c033ea10: 756e694c Linu
> crash>
>
> The linux_banner is at virtual address c033ea10 (addr). First it gets translated
> into physical address 33ea10 (paddr). Then that paddr is translated into the
> vmcore file offset of 33f088. It lseeks to vmcore file offset 33f088 and
> reads 4 bytes, which contain "756e694c", or the first 4 bytes of the
> "Linux version ..." string.
>
> Note that if I subtract the physical address from vmcore file offset
> I get this:
>
> crash> eval 33f088 - 33ea10
> hexadecimal: 678
> decimal: 1656
> octal: 3170
> binary: 00000000000000000000011001111000
> crash>
>
> which would put physical address 0 at a vmcore file offset of 0x678, and
> therefore implying that that the ELF header comprises the first 0x678 bytes.
> And looking at the vmcore, that can be verified:
>

yes you are right, here i get the result as below:

crash> set debug 8
debug: 8
crash> rd linux_banner
<addr: c065a071 count: 1 flag: 488 (KVADDR)>
<readmem: c065a071, KVADDR, "32-bit KVADDR", 4, (FOE), ffdf297c>
<read_kdump: addr: c065a071 paddr: 85a071 cnt: 4>
read_netdump: addr: c065a071 paddr: 85a071 cnt: 4 offset: 65a0e5
c065a071: 03e59130 0...

the virtual address is 0xc065a071 , and the physical address is 0x85a071 , and the offset is 0x65a0e5.

my elf header is 116 bytes long, 0x65a0e5 - 116=0x65A071, which has a gap 0x00200000 with the physical address 0x85a071.

> $ readelf -a vmcore
> ELF Header:
> Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
> Class: ELF32
> Data: 2's complement, little endian
> Version: 1 (current)
> OS/ABI: UNIX - System V
> ABI Version: 0
> Type: CORE (Core file)
> Machine: ARM
> Version: 0x1
> Entry point address: 0x0
> Start of program headers: 52 (bytes into file)
> Start of section headers: 0 (bytes into file)
> Flags: 0x0
> Size of this header: 52 (bytes)
> Size of program headers: 32 (bytes)
> Number of program headers: 3
> Size of section headers: 0 (bytes)
> Number of section headers: 0
> Section header string table index: 0
>
> There are no sections in this file.
>
> There are no sections to group in this file.
>
> Program Headers:
> Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> NOTE 0x000094 0x00000000 0x004e345c 0x005e4 0x005e4 0
> LOAD 0x000678 0xc0000000 0x00000000 0x5600000 0x5600000 RWE 0
> LOAD 0x5600678 0xc5700000 0x05700000 0x100000 0x100000 RWE 0
> ...
>
> Note that the "Offset" value of the first PT_LOAD segment has a file offset
> value of 0x678.
>

here i got the result as below:

Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
NOTE 0x000000 0x00000000 0x00000000 0x00000 0x00000 0
LOAD 0x000074 0xc0000000 0x00200000 0x2fe00000 0x2fe00000 RWE 0

so the problem is i don't understand the elf header meaning accurately. if i modify code as below, everything is ok for me:

offset += sizeof(struct elf_phdr);
phdr->p_offset = offset+0x00200000;
phdr->p_vaddr = 0xc0000000;
phdr->p_paddr = 0x00200000;
phdr->p_filesz = phdr->p_memsz = MEMSIZE-0x00200000;

although my modification can make crash utility work well, i want to know exactly whether i am doing the right thing.

1. our platform has the ddr address from physical address 0x0.

2. when compiling Linux kernel, our platform set in .config file: CONFIG_PHYS_OFFSET=0x00200000

3. when Kernel crash, all ddr content will be dumped, from address 0x0~768MB. but kernel data starts from 0x00200000 actually.

my questions are:

1. whether my setting of ELF header is correct this time? the offset, paddr, and p_memsz ?

2. i am wondering how does crash utility translate virtual address to physical address before and after it get the kernel page table? before get kernel page table, does it calculate as : (virtual_addr - p_vaddr + p_paddr) ? after get kernel page table, does it walk through the page table and find out the real physical address accordingly?

3. my real purpose is to get the ftrace content from dump file by crash utility , but seem the command trace is not for this case, do i need to compile the extension "trace" of crash utility? is there any guide to follow?

> Another thing to do is to verify that your phys_base of 0x20000000
> is being properly seen. In the --minimal session, you can verify that
> by doing this:
>
> crash> help -m | grep phys_base
>
> Trying the above should yield some clues into the problem you're encountering.
>
> Dave
>
>
>
>
>
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