gdb/arm-linux-nat.c

/* GNU/Linux on ARM native support.
   Copyright 1999 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include "defs.h"
#include "inferior.h"
#include "gdbcore.h"
#include "gdb_string.h"

#include <sys/user.h>
#include <sys/ptrace.h>
#include <sys/utsname.h>

extern int arm_apcs_32;

#define		typeNone		0x00
#define		typeSingle		0x01
#define		typeDouble		0x02
#define		typeExtended		0x03
#define 	FPWORDS			28
#define		CPSR_REGNUM		16

typedef union tagFPREG
  {
    unsigned int fSingle;
    unsigned int fDouble[2];
    unsigned int fExtended[3];
  }
FPREG;

typedef struct tagFPA11
  {
    FPREG fpreg[8];		/* 8 floating point registers */
    unsigned int fpsr;		/* floating point status register */
    unsigned int fpcr;		/* floating point control register */
    unsigned char fType[8];	/* type of floating point value held in
				   floating point registers.  */
    int initflag;		/* NWFPE initialization flag.  */
  }
FPA11;

/* The following variables are used to determine the version of the
   underlying Linux operating system.  Examples:

   Linux 2.0.35                 Linux 2.2.12
   os_version = 0x00020023      os_version = 0x0002020c
   os_major = 2                 os_major = 2
   os_minor = 0                 os_minor = 2
   os_release = 35              os_release = 12

   Note: os_version = (os_major << 16) | (os_minor << 8) | os_release

   These are initialized using get_linux_version() from
   _initialize_arm_linux_nat().  */

static unsigned int os_version, os_major, os_minor, os_release;

static void
fetch_nw_fpe_single (unsigned int fn, FPA11 * fpa11, unsigned int *pmem)
{
  unsigned int mem[3];

  mem[0] = fpa11->fpreg[fn].fSingle;
  mem[1] = 0;
  mem[2] = 0;
  supply_register (F0_REGNUM + fn, (char *) &mem[0]);
}

static void
fetch_nw_fpe_double (unsigned int fn, FPA11 * fpa11, unsigned int *pmem)
{
  unsigned int mem[3];

  mem[0] = fpa11->fpreg[fn].fDouble[1];
  mem[1] = fpa11->fpreg[fn].fDouble[0];
  mem[2] = 0;
  supply_register (F0_REGNUM + fn, (char *) &mem[0]);
}

static void
fetch_nw_fpe_none (unsigned int fn, FPA11 * fpa11, unsigned int *pmem)
{
  unsigned int mem[3] =
  {0, 0, 0};

  supply_register (F0_REGNUM + fn, (char *) &mem[0]);
}

static void
fetch_nw_fpe_extended (unsigned int fn, FPA11 * fpa11, unsigned int *pmem)
{
  unsigned int mem[3];

  mem[0] = fpa11->fpreg[fn].fExtended[0];	/* sign & exponent */
  mem[1] = fpa11->fpreg[fn].fExtended[2];	/* ls bits */
  mem[2] = fpa11->fpreg[fn].fExtended[1];	/* ms bits */
  supply_register (F0_REGNUM + fn, (char *) &mem[0]);
}

static void
store_nw_fpe_single (unsigned int fn, FPA11 * fpa11)
{
  unsigned int mem[3];

  read_register_gen (F0_REGNUM + fn, (char *) &mem[0]);
  fpa11->fpreg[fn].fSingle = mem[0];
  fpa11->fType[fn] = typeSingle;
}

static void
store_nw_fpe_double (unsigned int fn, FPA11 * fpa11)
{
  unsigned int mem[3];

  read_register_gen (F0_REGNUM + fn, (char *) &mem[0]);
  fpa11->fpreg[fn].fDouble[1] = mem[0];
  fpa11->fpreg[fn].fDouble[0] = mem[1];
  fpa11->fType[fn] = typeDouble;
}

void
store_nw_fpe_extended (unsigned int fn, FPA11 * fpa11)
{
  unsigned int mem[3];

  read_register_gen (F0_REGNUM + fn, (char *) &mem[0]);
  fpa11->fpreg[fn].fExtended[0] = mem[0];	/* sign & exponent */
  fpa11->fpreg[fn].fExtended[2] = mem[1];	/* ls bits */
  fpa11->fpreg[fn].fExtended[1] = mem[2];	/* ms bits */
  fpa11->fType[fn] = typeDouble;
}

/* Get the whole floating point state of the process and store the
   floating point stack into registers[].  */

static void
fetch_fpregs (void)
{
  int ret, regno;
  FPA11 fp;

  /* Read the floating point state.  */
  ret = ptrace (PT_GETFPREGS, inferior_pid, 0, &fp);
  if (ret < 0)
    {
      warning ("Unable to fetch the floating point state.");
      return;
    }

  /* Fetch fpsr.  */
  supply_register (FPS_REGNUM, (char *) &fp.fpsr);

  /* Fetch the floating point registers.  */
  for (regno = F0_REGNUM; regno <= F7_REGNUM; regno++)
    {
      int fn = regno - F0_REGNUM;
      unsigned int *p = (unsigned int *) &registers[REGISTER_BYTE (regno)];

      switch (fp.fType[fn])
	{
	case typeSingle:
	  fetch_nw_fpe_single (fn, &fp, p);
	  break;

	case typeDouble:
	  fetch_nw_fpe_double (fn, &fp, p);
	  break;

	case typeExtended:
	  fetch_nw_fpe_extended (fn, &fp, p);
	  break;

	default:
	  fetch_nw_fpe_none (fn, &fp, p);
	}
    }
}

/* Save the whole floating point state of the process using
   the contents from registers[].  */

static void
store_fpregs (void)
{
  int ret, regno;
  unsigned int mem[3];
  FPA11 fp;

  /* Store fpsr.  */
  if (register_valid[FPS_REGNUM])
    read_register_gen (FPS_REGNUM, (char *) &fp.fpsr);

  /* Store the floating point registers.  */
  for (regno = F0_REGNUM; regno <= F7_REGNUM; regno++)
    {
      if (register_valid[regno])
	{
	  unsigned int fn = regno - F0_REGNUM;
	  switch (fp.fType[fn])
	    {
	    case typeSingle:
	      store_nw_fpe_single (fn, &fp);
	      break;

	    case typeDouble:
	      store_nw_fpe_double (fn, &fp);
	      break;

	    case typeExtended:
	      store_nw_fpe_extended (fn, &fp);
	      break;
	    }
	}
    }

  ret = ptrace (PTRACE_SETFPREGS, inferior_pid, 0, &fp);
  if (ret < 0)
    {
      warning ("Unable to store floating point state.");
      return;
    }
}

/* Fetch all general registers of the process and store into
   registers[].  */

static void
fetch_regs (void)
{
  int ret, regno;
  struct pt_regs regs;

  ret = ptrace (PTRACE_GETREGS, inferior_pid, 0, &regs);
  if (ret < 0)
    {
      warning ("Unable to fetch general registers.");
      return;
    }

  for (regno = A1_REGNUM; regno < PC_REGNUM; regno++)
    supply_register (regno, (char *) &regs.uregs[regno]);

  if (arm_apcs_32)
    supply_register (PS_REGNUM, (char *) &regs.uregs[CPSR_REGNUM]);
  else
    supply_register (PS_REGNUM, (char *) &regs.uregs[PC_REGNUM]);

  regs.uregs[PC_REGNUM] = ADDR_BITS_REMOVE (regs.uregs[PC_REGNUM]);
  supply_register (PC_REGNUM, (char *) &regs.uregs[PC_REGNUM]);
}

/* Store all general registers of the process from the values in
   registers[].  */

static void
store_regs (void)
{
  int ret, regno;
  struct pt_regs regs;

  ret = ptrace (PTRACE_GETREGS, inferior_pid, 0, &regs);
  if (ret < 0)
    {
      warning ("Unable to fetch general registers.");
      return;
    }

  for (regno = A1_REGNUM; regno <= PC_REGNUM; regno++)
    {
      if (register_valid[regno])
	read_register_gen (regno, (char *) &regs.uregs[regno]);
    }

  ret = ptrace (PTRACE_SETREGS, inferior_pid, 0, &regs);

  if (ret < 0)
    {
      warning ("Unable to store general registers.");
      return;
    }
}

/* Fetch registers from the child process.  Fetch all registers if
   regno == -1, otherwise fetch all general registers or all floating
   point registers depending upon the value of regno.  */

void
fetch_inferior_registers (int regno)
{
  if ((regno < F0_REGNUM) || (regno > FPS_REGNUM))
    fetch_regs ();

  if (((regno >= F0_REGNUM) && (regno <= FPS_REGNUM)) || (regno == -1))
    fetch_fpregs ();
}

/* Store registers back into the inferior.  Store all registers if
   regno == -1, otherwise store all general registers or all floating
   point registers depending upon the value of regno.  */

void
store_inferior_registers (int regno)
{
  if ((regno < F0_REGNUM) || (regno > FPS_REGNUM))
    store_regs ();

  if (((regno >= F0_REGNUM) && (regno <= FPS_REGNUM)) || (regno == -1))
    store_fpregs ();
}

#ifdef GET_LONGJMP_TARGET

/* Figure out where the longjmp will land.  We expect that we have
   just entered longjmp and haven't yet altered r0, r1, so the
   arguments are still in the registers.  (A1_REGNUM) points at the
   jmp_buf structure from which we extract the pc (JB_PC) that we will
   land at.  The pc is copied into ADDR.  This routine returns true on
   success. */

#define LONGJMP_TARGET_SIZE 	sizeof(int)
#define JB_ELEMENT_SIZE		sizeof(int)
#define JB_SL			18
#define JB_FP			19
#define JB_SP			20
#define JB_PC			21

int
arm_get_longjmp_target (CORE_ADDR * pc)
{
  CORE_ADDR jb_addr;
  char buf[LONGJMP_TARGET_SIZE];

  jb_addr = read_register (A1_REGNUM);

  if (target_read_memory (jb_addr + JB_PC * JB_ELEMENT_SIZE, buf,
			  LONGJMP_TARGET_SIZE))
    return 0;

  *pc = extract_address (buf, LONGJMP_TARGET_SIZE);
  return 1;
}

#endif /* GET_LONGJMP_TARGET */

/*
   Dynamic Linking on ARM Linux
   ----------------------------

   Note: PLT = procedure linkage table
   GOT = global offset table

   As much as possible, ELF dynamic linking defers the resolution of
   jump/call addresses until the last minute. The technique used is
   inspired by the i386 ELF design, and is based on the following
   constraints.

   1) The calling technique should not force a change in the assembly
   code produced for apps; it MAY cause changes in the way assembly
   code is produced for position independent code (i.e. shared
   libraries).

   2) The technique must be such that all executable areas must not be
   modified; and any modified areas must not be executed.

   To do this, there are three steps involved in a typical jump:

   1) in the code
   2) through the PLT
   3) using a pointer from the GOT

   When the executable or library is first loaded, each GOT entry is
   initialized to point to the code which implements dynamic name
   resolution and code finding.  This is normally a function in the
   program interpreter (on ARM Linux this is usually ld-linux.so.2,
   but it does not have to be).  On the first invocation, the function
   is located and the GOT entry is replaced with the real function
   address.  Subsequent calls go through steps 1, 2 and 3 and end up
   calling the real code.

   1) In the code: 

   b    function_call
   bl   function_call

   This is typical ARM code using the 26 bit relative branch or branch
   and link instructions.  The target of the instruction
   (function_call is usually the address of the function to be called.
   In position independent code, the target of the instruction is
   actually an entry in the PLT when calling functions in a shared
   library.  Note that this call is identical to a normal function
   call, only the target differs.

   2) In the PLT:

   The PLT is a synthetic area, created by the linker. It exists in
   both executables and libraries. It is an array of stubs, one per
   imported function call. It looks like this:

   PLT[0]:
   str     lr, [sp, #-4]!       @push the return address (lr)
   ldr     lr, [pc, #16]   @load from 6 words ahead
   add     lr, pc, lr      @form an address for GOT[0]
   ldr     pc, [lr, #8]!   @jump to the contents of that addr

   The return address (lr) is pushed on the stack and used for
   calculations.  The load on the second line loads the lr with
   &GOT[3] - . - 20.  The addition on the third leaves:

   lr = (&GOT[3] - . - 20) + (. + 8)
   lr = (&GOT[3] - 12)
   lr = &GOT[0]

   On the fourth line, the pc and lr are both updated, so that:

   pc = GOT[2]
   lr = &GOT[0] + 8
   = &GOT[2]

   NOTE: PLT[0] borrows an offset .word from PLT[1]. This is a little
   "tight", but allows us to keep all the PLT entries the same size.

   PLT[n+1]:
   ldr     ip, [pc, #4]    @load offset from gotoff
   add     ip, pc, ip      @add the offset to the pc
   ldr     pc, [ip]        @jump to that address
   gotoff: .word   GOT[n+3] - .

   The load on the first line, gets an offset from the fourth word of
   the PLT entry.  The add on the second line makes ip = &GOT[n+3],
   which contains either a pointer to PLT[0] (the fixup trampoline) or
   a pointer to the actual code.

   3) In the GOT:

   The GOT contains helper pointers for both code (PLT) fixups and
   data fixups.  The first 3 entries of the GOT are special. The next
   M entries (where M is the number of entries in the PLT) belong to
   the PLT fixups. The next D (all remaining) entries belong to
   various data fixups. The actual size of the GOT is 3 + M + D.

   The GOT is also a synthetic area, created by the linker. It exists
   in both executables and libraries.  When the GOT is first
   initialized , all the GOT entries relating to PLT fixups are
   pointing to code back at PLT[0].

   The special entries in the GOT are:

   GOT[0] = linked list pointer used by the dynamic loader
   GOT[1] = pointer to the reloc table for this module
   GOT[2] = pointer to the fixup/resolver code

   The first invocation of function call comes through and uses the
   fixup/resolver code.  On the entry to the fixup/resolver code:

   ip = &GOT[n+3]
   lr = &GOT[2]
   stack[0] = return address (lr) of the function call
   [r0, r1, r2, r3] are still the arguments to the function call

   This is enough information for the fixup/resolver code to work
   with.  Before the fixup/resolver code returns, it actually calls
   the requested function and repairs &GOT[n+3].  */

CORE_ADDR
arm_skip_solib_resolver (CORE_ADDR pc)
{
  /* FIXME */
  return 0;
}

int
arm_linux_register_u_addr (int blockend, int regnum)
{
  return blockend + REGISTER_BYTE (regnum);
}

int
arm_linux_kernel_u_size (void)
{
  return (sizeof (struct user));
}

/* Extract from an array REGBUF containing the (raw) register state
   a function return value of type TYPE, and copy that, in virtual format,
   into VALBUF.  */

void
arm_linux_extract_return_value (struct type *type,
				char regbuf[REGISTER_BYTES],
				char *valbuf)
{
  /* ScottB: This needs to be looked at to handle the different
     floating point emulators on ARM Linux.  Right now the code
     assumes that fetch inferior registers does the right thing for
     GDB.  I suspect this won't handle NWFPE registers correctly, nor
     will the default ARM version (arm_extract_return_value()).  */

  int regnum = (TYPE_CODE_FLT == TYPE_CODE (type)) ? F0_REGNUM : A1_REGNUM;
  memcpy (valbuf, &regbuf[REGISTER_BYTE (regnum)], TYPE_LENGTH (type));
}

static unsigned int
get_linux_version (unsigned int *vmajor,
		   unsigned int *vminor,
		   unsigned int *vrelease)
{
  struct utsname info;
  char *pmajor, *pminor, *prelease, *tail;

  if (-1 == uname (&info))
    {
      warning ("Unable to determine Linux version.");
      return -1;
    }

  pmajor = strtok (info.release, ".");
  pminor = strtok (NULL, ".");
  prelease = strtok (NULL, ".");

  *vmajor = (unsigned int) strtoul (pmajor, &tail, 0);
  *vminor = (unsigned int) strtoul (pminor, &tail, 0);
  *vrelease = (unsigned int) strtoul (prelease, &tail, 0);

  return ((*vmajor << 16) | (*vminor << 8) | *vrelease);
}

void
_initialize_arm_linux_nat (void)
{
  os_version = get_linux_version (&os_major, &os_minor, &os_release);
}