[Crash-utility] Problem in bt for ARM64

[Dave Anderson]

----- Original Message -----
> 
> ----- Original Message -----
> > Ok. I have seen this change in the pt_regs struct before but did not connect
> > it to this problem. I see these new field in pt_regs in earlier kernel
> > versions than 4.7, but it is probably backports. It really does not matter
> > for the solution of the problem. The following change works for me:
> > Change:
> > #define USER_EFRAME_OFFSET (304)
> > to:
> > #define USER_EFRAME_OFFSET (STRUCT_SIZE("pt_regs") + 16)
> > 
> > Then you might want to avoid the recalculation of the struct size. I think
> > your patch does the same thing.
> 
> Yeah, but doing it your way makes better sense.  In fact, I see that there's
> another commit coming down the pike in 4.14-rc1 that changes the size yet
> again:
> 
> diff --git a/arch/arm64/include/asm/ptrace.h
> b/arch/arm64/include/asm/ptrace.h
> index 11403fd..ee72aa9 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -119,6 +119,7 @@ struct pt_regs {
>         u64 syscallno;
>         u64 orig_addr_limit;
>         u64 unused;     // maintain 16 byte alignment
> +       u64 stackframe[2];
>  };
> 
> Thanks,
>   Dave

As it turns out, neither patch works for 4.14 with the kernel commit above.
The stackframe[2] addition essentially accounts for the 16 bytes at the
top of the stack. 

The pt_regs structure in 4.14 is 320 bytes:
    
  crash> pt_regs
  struct pt_regs {
      union {
          struct user_pt_regs user_regs;
          struct {
              u64 regs[31];
              u64 sp;
              u64 pc;
              u64 pstate;
          };
      };
      u64 orig_x0;
      s32 syscallno;
      u32 unused2;
      u64 orig_addr_limit;
      u64 unused;
      u64 stackframe[2];
  }
  SIZE: 320
  crash>
  
So for example, taking a user-space task with a stacktop address of ffff00000807c000: 
  
  crash> eval ffff00000807c000 - 320
  hexadecimal: ffff00000807bec0  
      decimal: 18446462598867566272  (-281474841985344)
        octal: 1777770000001001737300
       binary: 1111111111111111000000000000000000001000000001111011111011000000
  crash>

Here is the pt_regs:
  
  crash> pt_regs ffff00000807bec0 -x
  struct pt_regs {
    {
      user_regs = {
        regs = {0x4, 0xffffe4ef4db0, 0x25, 0xffffffffffffffff, 0x0, 0x8, 0xffffffbb, 0x0, 0x16, 0x74, 0x65, 0x67, 0x10, 0x0, 0x1bb58f1f76129a, 0xce, 0xaaaaab21c660, 0xffffab4d35a8, 0xaaaaab1a0aa8, 0x4, 0x0, 0xffffe4ef4db0, 0x0, 0x1, 0xaaaaab180778, 0xaaaaab21c000, 0xaaaaab1803f0, 0xaaaaab21c000, 0xffffe4ef52b8, 0xffffe4ef4d70, 0xffffab4d3830}, 
        sp = 0xffffe4ef4d70, 
        pc = 0xffffab4d385c, 
        pstate = 0x80000000
      }, 
      {
        regs = {0x4, 0xffffe4ef4db0, 0x25, 0xffffffffffffffff, 0x0, 0x8, 0xffffffbb, 0x0, 0x16, 0x74, 0x65, 0x67, 0x10, 0x0, 0x1bb58f1f76129a, 0xce, 0xaaaaab21c660, 0xffffab4d35a8, 0xaaaaab1a0aa8, 0x4, 0x0, 0xffffe4ef4db0, 0x0, 0x1, 0xaaaaab180778, 0xaaaaab21c000, 0xaaaaab1803f0, 0xaaaaab21c000, 0xffffe4ef52b8, 0xffffe4ef4d70, 0xffffab4d3830}, 
        sp = 0xffffe4ef4d70, 
        pc = 0xffffab4d385c, 
        pstate = 0x80000000
      }
    }, 
    orig_x0 = 0x4, 
    syscallno = 0x16, 
    unused2 = 0x0, 
    orig_addr_limit = 0x0, 
    unused = 0x0, 
    stackframe = {0x0, 0x0}
  }
  crash> 
  
So for backwards compatibility, it will be necessary to look for the
new stackframe[2] field.

Unfortunately there have been some other significant changes to the 
unwind code in 4.14, and because of them, "bt" fails completely.

Dave