Re: PPC64 core-file GP register formats/order

[Wu Zhou <woodzltc at cn dot ibm dot com>]

Roland McGrath 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
>
> Ha!  Your optimism is quaint, dear fellow.  That might be true on as many
> as three or four architectures.  But that amount of consistency was only
> there to fool you into a false sense of security.

I guess gregset_t, which is defined in /usr/include/sys/ucontext.h as below, is the general answer.

 /* Type for general register.  */
typedef long int greg_t;

/* Number of general registers.  */
#define NGREG   23

/* Container for all general registers.  */
typedef greg_t gregset_t[NGREG];

On x86 and x86_64, an array to define the number of each register is followed:

#ifdef __USE_GNU
/* Number of each register in the `gregset_t' array.  */
enum
{
  REG_R8 = 0,
# define REG_R8         REG_R8
  REG_R9,
# define REG_R9         REG_R9
  REG_R10,
# define REG_R10        REG_R10
  REG_R11,
# define REG_R11        REG_R11
......

But on ppc64, there is no such an array in /usr/include/sys/ucontext.h.

> eu-readelf only has a tiny bit of core note format printing support,
> in fact only for i386 and x86_64.
>
> I'm not really sure what to tell you as the general answer to find this
> info.  I read the kernel source, but it's not so consistently written
> across different architectures that you can necessarily answer the question
> with the kernel source unless you are very familiar with reading it.
>
> For all the architectures you probably care about, it so happens I've
> already bothered to know, at least for one moment in the recent past.
> The core file note formats are the basis for the machine-specific
> "regset" format layouts in the utrace kernel interfaces.  I've had to
> recapitulate those layouts when writing format compatibility code in
> the userland test harness intended for developing modules based on
> utrace (the "ntrace" tarball in http://redhat.com/~roland/utrace/).
>
> For powerpc the elf_gregset_t format (sys/procfs.h) matches
> this kernel data structure (asm-powerpc/ptrace.h):
>
> struct pt_regs {
> 	unsigned long gpr[32];
> 	unsigned long nip;
> 	unsigned long msr;
> 	unsigned long orig_gpr3;	/* Used for restarting system calls */
> 	unsigned long ctr;
> 	unsigned long link;
> 	unsigned long xer;
> 	unsigned long ccr;
> #ifdef __powerpc64__
> 	unsigned long softe;		/* Soft enabled/disabled */
> #else
> 	unsigned long mq;		/* 601 only (not used at present) */
> 					/* Used on APUS to hold IPL value. */
> #endif
> 	unsigned long trap;		/* Reason for being here */
> 	/* N.B. for critical exceptions on 4xx, the dar and dsisr
> 	   fields are overloaded to hold srr0 and srr1. */
> 	unsigned long dar;		/* Fault registers */
> 	unsigned long dsisr;		/* on 4xx/Book-E used for ESR */
> 	unsigned long result;		/* Result of a system call */
> };

Same-named struct also exist in the system header file: /usr/include/asm-ppc64/ptrace.h, but there 
are two structures: one for 32-bit program, the other for 64-bit program:

#define PPC_REG unsigned long
struct pt_regs {
        PPC_REG gpr[32];
        PPC_REG nip;
        PPC_REG msr;
        PPC_REG orig_gpr3;      /* Used for restarting system calls */
        PPC_REG ctr;
        PPC_REG link;
        PPC_REG xer;
        PPC_REG ccr;
        PPC_REG softe;          /* Soft enabled/disabled */
        PPC_REG trap;           /* Reason for being here */
        PPC_REG dar;            /* Fault registers */
        PPC_REG dsisr;
        PPC_REG result;         /* Result of a system call */
};

#define PPC_REG_32 unsigned int
struct pt_regs32 {
        PPC_REG_32 gpr[32];
        PPC_REG_32 nip;
        PPC_REG_32 msr;
        PPC_REG_32 orig_gpr3;   /* Used for restarting system calls */
        PPC_REG_32 ctr;
        PPC_REG_32 link;
        PPC_REG_32 xer;
        PPC_REG_32 ccr;
        PPC_REG_32 mq;          /* 601 only (not used at present) */
                                /* Used on APUS to hold IPL value. */
        PPC_REG_32 trap;                /* Reason for being here */
        PPC_REG_32 dar;         /* Fault registers */
        PPC_REG_32 dsisr;
        PPC_REG_32 result;      /* Result of a system call */
};

It looks the same as the kernel strucuture.

Though, there is one problem confusing me all the time: why asm-powerpc replace asm-ppc64 in the kernel?

Regards
- Wu Zhou