[Crash-utility] [PATCH] filesys: Skip 'vmlinux.o' while searching for vmlinux in 'find_booted_kernel()'
Dave Anderson
anderson at redhat.com
Wed Feb 28 15:39:25 UTC 2018
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
----- 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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