[Crash-utility] crash on ppc docs / pointers

[Dave Anderson]

----- "Bryn M. Reeves" <bmr at redhat.com> wrote:

> Hi Folks,
> 
> I have some experience using crash on x86/x86_64 cores but I'm pretty
> new to ppc64. I'm making some headway, but a bit confused by some
> things.
> 
> E.g., I have a function that calls kfree, so when I disassemble it,
> I'm expecting to see something like:
> 
> bl <address of .kfree>
> 
> But instead I find:
> 
> 0xd000000000bd3b00 bl      0xd000000000bd4120
> 
> Where that address lies inside .init_module:
> 
> crash> sym 0xd000000000bd4120
> d000000000bd4120 (T) .init_module+496
> 
> .kfree is somewhere else entirely:
> crash> sym .kfree
> c0000000000ed0b4 (T) .kfree
> 
> I'm pretty certain this is the call to kfree that I'm interested in
> (LR points at the next instruction and we oopsed inside kfree).
> 
> Is there some sort of indirection here that I'm missing?

Apparently so, at least with respect to kernel module code calling into
the base kernel.  Here's a call to kmalloc() in ext3_xattr_block_set(),
where kmalloc() is actually an inline in slab.h that calls __kmalloc(): 

  crash> dis -l .ext3_xattr_block_set
  ...
  /usr/src/debug/kernel-2.6.18/linux-2.6.18.ppc64/fs/ext3/xattr.c: 724
  0xd00000000019671c <.ext3_xattr_block_set+548>: ld      r9,40(r26)
  include/linux/slab.h: 154
  0xd000000000196720 <.ext3_xattr_block_set+552>: li      r4,208
  0xd000000000196724 <.ext3_xattr_block_set+556>: ld      r3,32(r9)
  0xd000000000196728 <.ext3_xattr_block_set+560>: bl      0xd000000000199858
  ...

and looking around that "bl" target, there's the target function
address of ".__kmalloc" a few words after it:

  crash> rd -s 0xd000000000199858 20
  d000000000199858:  3d82fffe398ce448 f8410028e96c0020 
  d000000000199868:  e84c00287d6903a6 4e80042000000000 
  d000000000199878:  .__kmalloc       PPC64_CACHES+24336 
  d000000000199888:  3d82fffe398ce478 f8410028e96c0020 
  d000000000199898:  e84c00287d6903a6 4e80042000000000 
  d0000000001998a8:  .memset          PPC64_CACHES+24336 
  d0000000001998b8:  3d82fffe398ce4a8 f8410028e96c0020 
  d0000000001998c8:  e84c00287d6903a6 4e80042000000000 
  d0000000001998d8:  .memcpy          PPC64_CACHES+24336 
  d0000000001998e8:  3d82fffe398ce4d8 f8410028e96c0020 
  crash> 

So I presume if you look at the data around 0xd000000000bd4120, you'll
most likely see ".kfree".

Dave