[Crash-utility] [PATCH] arm64: exclude mapping symbols in modules

[AKASHI Takahiro]

Dave,

One question.

On Tue, Oct 04, 2016 at 11:00:16AM -0400, Dave Anderson wrote:
> 
> 
> ----- Original Message -----
> > If some module has been inserted, crash util complains about
> > module symbols:
> >     ...
> >     please wait... (gathering module symbol data)
> >     crash: store_module_symbols_v2: total: 15 mcnt: 16
> > and end up with stopping.
> > 
> > This patch excludes mapping symbols, like $d and $x, as arm does.

On arm64, when KASLR is enabled, a function call between a module and
the kernel will be done via a veneer (PLT) if the displacement is more
than +/-128MB. So disassembled code looks a bit useless:

===8<===
crash> mod -S
     MODULE       NAME      SIZE  OBJECT FILE
ffff04d78f4b8000  testmod  16384  /opt/buildroot/15.11_64/root/kexec/testmod.ko 
crash> bt  
PID: 1102   TASK: ffffb4da8e910000  CPU: 0   COMMAND: "insmod"
 #0 [ffffb4da8e9afa30] __crash_kexec at ffff0e0045020a54
 #1 [ffffb4da8e9afb90] panic at ffff0e004505523c
 #2 [ffffb4da8e9afc50] testmod_init at ffff04d78f4b6014 [testmod]
 #3 [ffffb4da8e9afb40] do_one_initcall at ffff0e0044f7333c
--- <Exception in user> ---
     PC: 0000000a  LR: 00000000  SP: ffff04d78f4b6000  PSTATE: 7669726420656c75
    X12: ffffb4da8e9ac000 X11: ffff04d78f4b6018 X10: ffffb4da8e9afc50  X9: 20676e6973756143
     X8: 00000000  X7: ffff0e0045e5ce00  X6: ffff0e0045e5c000  X5: 600001c5
     X4: ffff0e0045020a58  X3: ffffb4da8e9afa30  X2: ffff0e004502098c  X1: ffffb4da8e9afa30
     X0: 00000124
crash> dis testmod_init
0xffff04d78f4b6000 <init_module>:       stp     x29, x30, [sp,#-16]!
0xffff04d78f4b6004 <testmod_init+4>:    mov     x29, sp
0xffff04d78f4b6008 <testmod_init+8>:    ldr     x0, 0xffff04d78f4b6018
0xffff04d78f4b600c <testmod_init+12>:   bl      0xffff04d78f4b6090
0xffff04d78f4b6010 <testmod_init+16>:   ldr     x0, 0xffff04d78f4b6020
0xffff04d78f4b6014 <testmod_init+20>:   bl      0xffff04d78f4b6080

						=> branch to a veneer
crash> dis 0xffff04d78f4b6080 4

0xffff04d78f4b6080 <testmod_exit+88>:   mov     x16, #0xffffffffffff5120        // #-44768
0xffff04d78f4b6084 <testmod_exit+92>:   movk    x16, #0x4505, lsl #16
0xffff04d78f4b6088 <testmod_exit+96>:   movk    x16, #0xe00, lsl #32
0xffff04d78f4b608c <testmod_exit+100>:  br      x16

						=> branch to 0xffff0e0045055120
							     (= panic())
===>8===

Is there any method to resolve such kind of indirect addressing
to a symbolic name at dis command?
(It may be difficult to discriminate PLT from normal branches, though).

Thanks,
-Takahiro AKASHI


> > Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> 
> Queued for crash-7.1.6:
> 
>   https://github.com/crash-utility/crash/commit/9a5cbfe998060a8f99997b1e463353abcfcf1fce
> 
> Thanks,
>   Dave
> 
>   
> > ---
> >  symbols.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/symbols.c b/symbols.c
> > index 99c8b8b..a657ead 100644
> > --- a/symbols.c
> > +++ b/symbols.c
> > @@ -2251,10 +2251,11 @@ store_module_kallsyms_v2(struct load_module *lm, int
> > start, int curr,
> >  			continue;
> >  
> >  		/*
> > -		 * On ARM we have linker mapping symbols like '$a' and '$d'.
> > +		 * On ARM/ARM64 we have linker mapping symbols like '$a'
> > +		 * or '$x' for ARM64, and '$d'.
> >  		 * Make sure that these don't end up into our symbol list.
> >  		 */
> > -		if (machine_type("ARM") &&
> > +		if ((machine_type("ARM") || machine_type("ARM64")) &&
> >  		    !machdep->verify_symbol(nameptr, ec->st_value, ec->st_info))
> >  			continue;
> >  
> > --
> > 2.10.0
> > 
> > --
> > Crash-utility mailing list
> > Crash-utility at redhat.com
> > https://www.redhat.com/mailman/listinfo/crash-utility
> > 
> 
> --
> Crash-utility mailing list
> Crash-utility at redhat.com
> https://www.redhat.com/mailman/listinfo/crash-utility