Re: PPC64 core-file GP register formats/order

[Yong Zheng <zhengyo@cn.ibm.com>]

On Sun, 2006-10-22 at 20:38 -0500, Phil Muldoon wrote: 
> I'm not sure what to do, but I cannot find the expectations of register 
> order in a core file for PPC64. On other architectures the order is 
> defined in:
> 
> struct user_regs_struct
> {..structure defined here...}
> 
> in /usr/include/asm/user.h
> 
> in x86, and on x86_64:
> 
> asm-i386/    asm-x86_64/
> 
> Depending on how that box is configured.
> 
> The only contents of user.h on a PPC64 box in Toronto contains:
> 
> #ifndef _ASM_POWERPC_USER_H
> #define _ASM_POWERPC_USER_H
> #endif  /* _ASM_POWERPC_USER_H */
> 


IMO, the PRSTATUS data struct is defined by the struct elf_prstatus in
<linux/elfcore.h>, right?(I think it's right, you know kernel dumps core
file according <linux/elfcore.h>, so we should take the same struct as
kernel does). Then the attribute "elf_gregset_t pr_reg" is referred in
the struct elf_prstatus.

On x86/x86_64, the "elf_gregset_t pr_reg" is defined by the struct
"struct user_regs_struct" in <asm-i386/user.h> or <asm-x86_64/user.h>.
We should dump out the registers according to the "struct
user_regs_struct". This is ok, you must have done this. :-)

Unfortunately in the <asm-ppc64/user.h> on PPC64, no one struct like
"struct user_regs_struct" is defined. So this will bring us some
troubles when dumping. 

Let go back to read the <linux/elfcore.h>. On PPC/PPC64, the struct
"elf_gregset_t" is defined as one unsigned long array with the size of
48 in <asm-ppc64/elf.h> or <asm-ppc/elf.h>. And about each member in the
array is defined in <asm-ppc/ptrace.h> or <asm-ppc64/ptrace.h>, for
example, the array[0] is the NO.0 general purpose register(i.e. gpr0). I
think we should take this order to dump out the attribute "elf_gregset_t
pr_reg" of PRSTATUS.

Now the question becomes how to get the above 48 registers' value on
PPC64. (I'm not sure how you get the similar value on X86/X86_64. We
guess you get them by getRegisterBankBuffers() in ISA.java. :-)). If you
get them by getRegisterBankBuffers() in ISA.java, it will more easier
for us to get the same registerBankBuffer on PPC64.So, if the code works
well on X86/X86_64, please check them in. And we will do some
modifications for PPC64.


> I tried to backward engineer the order with gcore and kernel on ppc64, 
> but both of those either do not write notes, or eu-readelf cannot 
> understand them as the output is:
> 
> Note segment of 2060 bytes at offset 0x2b4:
>   Owner          Data size  Type
>   CORE                 268  PRSTATUS
>   CORE                 128  PRPSINFO
> 
> That is basically no note data at all (or that can be understood).
> 

I do one test for kernel' core dump file on PPC64. THe tool "en-readelf" cannot 
recogonize the PRSTATUS's detailed information, it just shows some general info like the above.
I think this may be the bug in en-readelf on PPC64.

Best regards
Yong Zheng