New subject: crash on ppc docs / pointers

Wednesday, 25 February 2009

----- "Bryn M. Reeves" <bmr(a)redhat.com&gt; 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

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Re: [Crash-utility] crash on ppc docs / pointers