On Thu, Mar 12, 2020 at 3:18 AM Mikhail Petrov <Mikhail.Petrov@xxxxxxx> wrote:
>
> Hi Masahiro,
>
> On 11.03.2020 9:06, Masahiro Yamada wrote:
> > Hi Mikhail,
> >
> > On Wed, Mar 11, 2020 at 5:34 AM Mikhail Petrov <Mikhail.Petrov@xxxxxxx> wrote:
> >>
> >> There is the code in the read_symbol function in 'scripts/kallsyms.c':
> >>
> >> if (is_ignored_symbol(name, type))
> >> return NULL;
> >>
> >> /* Ignore most absolute/undefined (?) symbols. */
> >> if (strcmp(name, "_text") == 0)
> >> _text = addr;
> >>
> >> But the is_ignored_symbol function returns true for name="_text" and type='a'. So the next condition is not executed and the _text variable is always zero.
> >>
> >> It makes the wrong kallsyms_relative_base symbol as a result of the code:
> >>
> >> if (base_relative) {
> >> output_label("kallsyms_relative_base");
> >> output_address(relative_base);
> >> printf("\n");
> >> }
> >>
> >> Because the output_address function uses the _text variable.
> >>
> >> So the kallsyms_lookup function and all related functions in the kernel do not work properly. For example, the stack trace in oops:
> >>
> >> Call Trace:
> >> [aa095e58] [809feab8] kobj_ns_ops_tbl+0x7ff09ac8/0x7ff1c1c4 (unreliable)
> >> [aa095e98] [80002b64] kobj_ns_ops_tbl+0x7f50db74/0x80000010
> >> [aa095ef8] [809c3d24] kobj_ns_ops_tbl+0x7feced34/0x7ff1c1c4
> >> [aa095f28] [80002ed0] kobj_ns_ops_tbl+0x7f50dee0/0x80000010
> >> [aa095f38] [8000f238] kobj_ns_ops_tbl+0x7f51a248/0x80000010
> >>
> >> The right stack trace:
> >>
> >> Call Trace:
> >> [aa095e58] [809feab8] module_vdu_video_init+0x2fc/0x3bc (unreliable)
> >> [aa095e98] [80002b64] do_one_initcall+0x40/0x1f0
> >> [aa095ef8] [809c3d24] kernel_init_freeable+0x164/0x1d8
> >> [aa095f28] [80002ed0] kernel_init+0x14/0x124
> >> [aa095f38] [8000f238] ret_from_kernel_thread+0x14/0x1c
> >>
> >> Signed-off-by: Mikhail Petrov <Mikhail.Petrov@xxxxxxx>
> >>
> >> ---
> >
> >
> > Thanks for the patch.
> >
> > Just for curiosity, on which architecrure
> > did you see name="_text" and type='a' case ?
>
> Actually 'a' is 'A' (my mistake). The architecture is PowerPC - core PPC476FS.
>
> nm -n .tmp_vmlinux1 looks like:
>
> ...
> w kallsyms_token_table
> w mach_powermac
> 00000007 a LG_CACHELINE_BYTES
> 00000007 a LG_CACHELINE_BYTES
> 00000007 a LG_CACHELINE_BYTES
> 00000020 a reg
> 0000007f a CACHELINE_MASK
> 0000007f a CACHELINE_MASK
> 0000007f a CACHELINE_MASK
> 00000080 a CACHELINE_BYTES
> 00000080 a CACHELINE_BYTES
> 00000080 a CACHELINE_BYTES
> 00000400 a dcr
> 80000000 T _start
> 80000000 A _stext
> 80000000 A _text
Hmm, I am still not able to reproduce this.
I compiled ARCH=powerpc, but
'powerpc-linux-nm -n .tmp_vmlinux1' got this.
0000007f a CACHELINE_MASK
0000007f a CACHELINE_MASK
0000007f a CACHELINE_MASK
00000080 a CACHELINE_BYTES
00000080 a CACHELINE_BYTES
00000080 a CACHELINE_BYTES
00000400 a dcr
c0000000 T _start
c0000000 T _stext
c0000000 T _text
c00000b8 t interrupt_base
c00000c0 t CriticalInput
c00001a0 t MachineCheck
c0000280 t MachineCheckA
Which defconfig did you use?
(I also CCed the ppc maintainer,
I am just curious what makes _text absolute.)
> 80000088 t interrupt_base
> 800000a0 t CriticalInput
> 80000180 t MachineCheck
> 80000260 t MachineCheckA
> 80000360 t DataStorage
> 80000420 t InstructionStorage
> 80000500 t ExternalInput
> 800005c0 t Alignment
> 80000680 t Program
> 80000740 t FloatingPointUnavailable
> 80000820 t SystemCall
> 80000900 t AuxillaryProcessorUnavailable
> ...
>
>
> > Could you wrap the commit log to avoid
> > this checkpatch warning?
> > WARNING: Possible unwrapped commit description (prefer a maximum 75
> > chars per line)
> >
> > Also, could you shorten the patch subject
> > to make it fit in this limit?
>
> Sorry for that. Now I know about scripts/checkpatch.pl. I will improve and resubmit the patch soon.
>
> Thanks.
--
Best Regards
Masahiro Yamada
