[Crash-utility] [PATCH] filesys: Skip 'vmlinux.o' while searching for vmlinux in 'find_booted_kernel()'
Bhupesh Sharma
bhsharma at redhat.com
Wed Feb 28 19:35:56 UTC 2018
Hi Dave,
On Wed, Feb 28, 2018 at 9:09 PM, Dave Anderson <anderson at redhat.com> wrote:
>
> Hi Bhupesh,
>
> Try this patch:
>
> $ diff --git a/filesys.c b/filesys.c
> index 1b44ad5..74728f1
> --- a/filesys.c
> +++ b/filesys.c
> @@ -625,7 +625,7 @@ find_booted_kernel(void)
>
> if (mount_point(kernel) ||
> !file_readable(kernel) ||
> - !is_elf_file(kernel))
> + !is_kernel(kernel))
> continue;
>
> if (CRASHDEBUG(1))
> diff --git a/symbols.c b/symbols.c
> index 4db9af7..7910f53
> --- a/symbols.c
> +++ b/symbols.c
> @@ -3488,7 +3488,8 @@ is_kernel(char *file)
>
> if (endian_mismatch(file, elf64->e_ident[EI_DATA], 0))
> goto bailout;
> - }
> + } else
> + return FALSE;
>
> bailout:
> return(is_bfd_format(file));
>
> Thanks,
> Dave
I tried this patch and it seems to work fine on my arm64 system.
Please feel free to add my Tested-by for the patch.
Thanks.
> ----- Original Message -----
>> Hi Bhupesh,
>>
>> Thanks -- mystery solved!
>>
>> I kind of hate to simply use the file name string as the qualifier, though.
>> Looking at the ELF headers of the vmlinux.o and vmlinux file, there are
>> several notable differences:
>>
>> $ readelf -a vmlinux
>> ELF Header:
>> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
>> Class: ELF64
>> Data: 2's complement, little endian
>> Version: 1 (current)
>> OS/ABI: UNIX - System V
>> ABI Version: 0
>> Type: EXEC (Executable file)
>> Machine: AArch64
>> Version: 0x1
>> Entry point address: 0xffff000008080000
>> Start of program headers: 64 (bytes into file)
>> Start of section headers: 186677936 (bytes into file)
>> Flags: 0x0
>> Size of this header: 64 (bytes)
>> Size of program headers: 56 (bytes)
>> Number of program headers: 4
>> Size of section headers: 64 (bytes)
>> Number of section headers: 42
>> Section header string table index: 41
>> ...
>>
>>
>> $ readelf -a vmlinux.o
>> ELF Header:
>> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
>> Class: ELF64
>> Data: 2's complement, little endian
>> Version: 1 (current)
>> OS/ABI: UNIX - System V
>> ABI Version: 0
>> Type: REL (Relocatable file)
>> Machine: AArch64
>> Version: 0x1
>> Entry point address: 0x0
>> Start of program headers: 0 (bytes into file)
>> Start of section headers: 478638376 (bytes into file)
>> Flags: 0x0
>> Size of this header: 64 (bytes)
>> Size of program headers: 0 (bytes)
>> Number of program headers: 0
>> Size of section headers: 64 (bytes)
>> Number of section headers: 34816
>> Section header string table index: 34815
>> ...
>>
>> There is the "Type", the "Entry point address", and perhaps most notably,
>> the vmlinux.o's "Number of program headers:" count of 0, which obviously
>> would preclude the file from being usable.
>>
>> I would prefer to beef up the currently-existing is_kernel() function,
>> and use it instead of is_elf_file(). Let me take a look at what works.
>>
>> Thanks,
>> Dave
>>
>>
>>
>> ----- Original Message -----
>> > I found this particular issue while compiling and installing
>> > a kernel from source on a RHEL arm64 machine. I used the following
>> > commands to build and install the kernel from source:
>> >
>> > # make olddefconfig
>> > # make
>> > # make modules_install INSTALL_MOD_STRIP=1 && make install
>> >
>> > This compiles and installs both 'vmlinux' and 'vmlinux.o' at
>> > the following standard location - '/lib/modules/<kernel>/build/
>> >
>> > Now the problem can be reproduced using the following steps:
>> > 1. Update grub to boot the freshly compiled kernel.
>> > 2. Reboot machine.
>> > 3. Now, run crash on live system, it errors out with the following
>> > messages:
>> >
>> > crash: invalid kernel virtual address: 8470 type: "possible"
>> > WARNING: cannot read cpu_possible_map
>> > crash: invalid kernel virtual address: 8270 type: "present"
>> > WARNING: cannot read cpu_present_map
>> > crash: invalid kernel virtual address: 8070 type: "online"
>> > WARNING: cannot read cpu_online_map
>> > crash: invalid kernel virtual address: 8670 type: "active"
>> > WARNING: cannot read cpu_active_map
>> >
>> > crash: cannot resolve "_stext"
>> >
>> > 4. Enabling some debug messages in 'find_booted_kernel()' function
>> > tells us that it finds 'vmlinux.o' earlier than 'vmlinux' and accepts
>> > that as the kernel being boot'ed:
>> >
>> > find_booted_kernel: check: /lib/modules/4.14.0/build/vmlinux.o
>> > find_booted_kernel: found: /lib/modules/4.14.0/build/vmlinux.o
>> >
>> > 5. Now the problem happens due to following check inside
>> > 'find_booted_kernel()' function:
>> >
>> > if (mount_point(kernel) ||
>> > !file_readable(kernel) ||
>> > !is_elf_file(kernel))
>> > continue;
>> >
>> > 6. Since 'vmlinux.o' is a elf file, is readable and is not
>> > mount'able, so the check in point 5 fails and we incorrectly
>> > accept this as the kernel being boot'ed, even though
>> > there was a 'vmlinux' present inside
>> > '/lib/modules/<kernel>/build'.
>> >
>> > 7. Now, later when crash tries to access symbols (like _stext)
>> > using this kernel symbol file, we see errors.
>> >
>> > Fix this by skipping 'vmlinux.o' from the check in point 5,
>> > so that we can select 'vmlinux' correctly as the kernel file.
>> >
>> > After this fix, crash no longer errors out and we can use
>> > full functionality on the crash prompt.
>> >
>> > Signed-off-by: Bhupesh Sharma <bhsharma at redhat.com>
>> > ---
>> > filesys.c | 14 +++++++++++++-
>> > 1 file changed, 13 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/filesys.c b/filesys.c
>> > index 1b44ad5cefa8..9f240d6115a1 100644
>> > --- a/filesys.c
>> > +++ b/filesys.c
>> > @@ -623,9 +623,21 @@ find_booted_kernel(void)
>> >
>> > sprintf(kernel, "%s%s", searchdirs[i], dp->d_name);
>> >
>> > + /* We may run into a special case with
>> > + * 'vmlinux.o' been present inside
>> > + * '/lib/modules/<kernel>/build/',
>> > + * which has some special characteristics -
>> > + * this is a elf file, is readable and is not
>> > + * mount'able.
>> > + *
>> > + * So we need to handle this properly here to
>> > + * make sure that we get to the real 'vmlinux'
>> > + * rather than the 'vmlinux.o'
>> > + */
>> > if (mount_point(kernel) ||
>> > !file_readable(kernel) ||
>> > - !is_elf_file(kernel))
>> > + !is_elf_file(kernel) ||
>> > + !(strcmp(dp->d_name, "vmlinux.o")))
>> > continue;
>> >
>> > if (CRASHDEBUG(1))
>> > --
>> > 2.7.4
>> >
>> >
>>
>> --
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>> Crash-utility at redhat.com
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>>
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