path: root/gdb/arc-linux-tdep.c

/* Target dependent code for ARC processor family, for GDB, the GNU debugger.

   Copyright 2005, 2008, 2009 Free Software Foundation, Inc.

   Contributed by Codito Technologies Pvt. Ltd. (www.codito.com)

   Authors:
      Soam Vasani          <soam.vasani@codito.com>
      Ramana Radhakrishnan <ramana.radhakrishnan@codito.com>
      Richard Stuckey      <richard.stuckey@arc.com>

   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 3 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, see <http://www.gnu.org/licenses/>.  */

/******************************************************************************/
/*                                                                            */
/* Outline:                                                                   */
/*     This module provides support for the ARC processor family's target     */
/*     dependencies which are specific to the arc-linux-uclibc configuration  */
/*     of the ARC gdb.                                                        */
/*                                                                            */
/* Functionality:                                                             */
/*     This module provides a number of operations, including:                */
/*                                                                            */
/*     1) a function which returns the name of a register, given its number   */
/*                                                                            */
/*     2) a function which determines whether a given register belongs to a   */
/*        particular group (e.g. the group of registers which should be saved */
/*        and restored across a function call)                                */
/*                                                                            */
/*     3) a function which prints out registers                               */
/*                                                                            */
/*                                                                            */
/* Usage:                                                                     */
/*     The module exports a function _initialize_arc_linux_tdep: the call to  */
/*     this function is generated by the gdb build mechanism, so this function*/
/*     should not be explicitly called.                                       */
/*                                                                            */
/*     Some of the operations provided by this module are registered with gdb */
/*     during initialization; gdb then calls them via function pointers,      */
/*     rather than by name (this allows gdb to handle multiple target         */
/*     architectures):                                                        */
/*                                                                            */
/*          set_gdbarch_XXX (gdbarch, <function>);                            */
/*                                                                            */
/*                                                                            */
/* Register Numbering Scheme:                                                 */
/*     The N target processor registers are assigned gdb numbers which form a */
/*     contiguous range starting at 0.  The scheme used is:                   */
/*                                                                            */
/*         0  .. 26  :  core registers R0 .. R26                              */
/*         27        :  BTA (Branch Target Address) auxiliary register        */
/*         28        :  LP_START auxiliary register                           */
/*         29        :  LP_END   auxiliary register                           */
/*         30        :  LP_COUNT core register            (R60)               */
/*         31        :  STATUS32 auxiliary register                           */
/*         32        :  BLINK (Branch Link) core register (R31)               */
/*         33        :  FP (Frame Pointer) core register  (R27)               */
/*         34        :  SP (Stack Pointer) core register  (R28)               */
/*         35        :  EFA (Exception Fault Address) auxiliary register      */
/*         36        :  RET (Exception Return Address) auxiliary register     */
/*         37        :  ORIG_R8                                               */
/*         38        :  STOP_PC                                               */
/*                                                                            */
/*     N.B. 1) core registers R61 and R62 are not included in the scheme, as  */
/*             R61 is reserved, and R62 is not a real register;               */
/*                                                                            */
/*          2) core registers R29 (ILINK1), R30 (ILINK2) and R63 (PCL) are    */
/*             not included;                                                  */
/*                                                                            */
/*          3) extension core registers R32 .. R59 are not included;          */
/*                                                                            */
/*          4) most auxiliary registers (including all Build Configuration    */
/*             Registers) are not included.                                   */
/*                                                                            */
/******************************************************************************/

/* gdb header files */
#include "defs.h"
#include "osabi.h"
#include "regcache.h"
#include "inferior.h"
#include "reggroups.h"
#include "solib-svr4.h"
#include "block.h"
#include "regset.h"
#include "dis-asm.h"
#include "opcode/arc.h"
#include "gdb_assert.h"

/* ARC header files */
#include "config/arc/tm-linux.h"
#include "arc-linux-tdep.h"
#include "arc-support.h"
#include "arc-tdep.h"
#include "opcodes/arcompact-dis.h"


/* -------------------------------------------------------------------------- */
/*                               local data                                   */
/* -------------------------------------------------------------------------- */

#define STATUS32_L            0x00000100


/* Default breakpoint instruction used for ARC700 Linux.  */
static const unsigned char le_breakpoint_instruction[] = { 0x3e, 0x78 };
static const unsigned char be_breakpoint_instruction[] = { 0x78, 0x3e };


/* This array holds the object code of two instructions:
      mov r8,nr_sigreturn
      swi
 */
static const gdb_byte arc_sigtramp_insns[] = { 0x8a, 0x20, 0xc1, 0x1d,
                                               0x6f, 0x22, 0x3f, 0x00 };

#define SIGTRAMP_INSNS_LENGTH     sizeof(arc_sigtramp_insns)


/* N.B. the array size is specified in the declaration so that the compiler
        will warn of "excess elements in array initializer" if there is a
        mismatch (but not of too few elements, unfortunately!).  */
static const char *register_names[ARC_NR_REGS + ARC_NR_PSEUDO_REGS] =
{
    "r0",  "r1",  "r2",  "r3",  "r4",  "r5",  "r6",
    "r7",  "r8",  "r9",  "r10", "r11", "r12", "r13",
    "r14", "r15", "r16", "r17", "r18", "r19", "r20",
    "r21", "r22", "r23", "r24", "r25", "r26",

    "bta",
    "lp_start",
    "lp_end",
    "lp_count",
    "status32",
    "blink",
    "fp",
    "sp",
    "efa",

    /* Linux-only registers.  */
    "ret",
    "orig_r8",
    "pc",           // stop pc

    /* Pseudo-regs.  */
    "ilink1",
    "ilink2",
    "eret",
    "status_l1",
    "status_l2",
    "erstatus"
};


/* Mapping between the general-purpose registers in `struct sigcontext' format
   and GDB's register cache layout.

   arc_linux_sc_reg_offset[i] is the sigcontext offset of GDB regnum `i'.  */

/* From <asm/sigcontext.h>.  */
static const int arc_linux_sc_reg_offset[ARC_NR_REGS] =
{
    23 * BYTES_IN_REGISTER,      /* r0       */
    22 * BYTES_IN_REGISTER,      /* r1       */
    21 * BYTES_IN_REGISTER,      /* r2       */
    20 * BYTES_IN_REGISTER,      /* r3       */
    19 * BYTES_IN_REGISTER,      /* r4       */
    18 * BYTES_IN_REGISTER,      /* r5       */
    17 * BYTES_IN_REGISTER,      /* r6       */
    16 * BYTES_IN_REGISTER,      /* r7       */
    15 * BYTES_IN_REGISTER,      /* r8       */
    14 * BYTES_IN_REGISTER,      /* r9       */
    13 * BYTES_IN_REGISTER,      /* r10      */
    12 * BYTES_IN_REGISTER,      /* r11      */
    11 * BYTES_IN_REGISTER,      /* r12      */
    REGISTER_NOT_PRESENT,        /* r13      */
    REGISTER_NOT_PRESENT,        /* r14      */
    REGISTER_NOT_PRESENT,        /* r15      */
    REGISTER_NOT_PRESENT,        /* r16      */
    REGISTER_NOT_PRESENT,        /* r17      */
    REGISTER_NOT_PRESENT,        /* r18      */
    REGISTER_NOT_PRESENT,        /* r19      */
    REGISTER_NOT_PRESENT,        /* r20      */
    REGISTER_NOT_PRESENT,        /* r21      */
    REGISTER_NOT_PRESENT,        /* r22      */
    REGISTER_NOT_PRESENT,        /* r23      */
    REGISTER_NOT_PRESENT,        /* r24      */
    REGISTER_NOT_PRESENT,        /* r25      */
    10 * BYTES_IN_REGISTER,      /* r26      */
     2 * BYTES_IN_REGISTER,      /* bta      */
     3 * BYTES_IN_REGISTER,      /* lp_start */
     4 * BYTES_IN_REGISTER,      /* lp_end   */
     5 * BYTES_IN_REGISTER,      /* lp_count */
     6 * BYTES_IN_REGISTER,      /* status32 */
     8 * BYTES_IN_REGISTER,      /* blink    */
     9 * BYTES_IN_REGISTER,      /* fp       */
     1 * BYTES_IN_REGISTER,      /* sp       */
    REGISTER_NOT_PRESENT,        /* efa      */
     7 * BYTES_IN_REGISTER,      /* ret      */
    REGISTER_NOT_PRESENT,        /* orig_r8  */
    REGISTER_NOT_PRESENT         /* stop_pc  */
};


/* arcompact_linux_core_reg_offsets[i] is the offset in the .reg section of GDB regnum i.
   From include/asm-arc/user.h in the ARC Linux sources.  */

static const int arcompact_linux_core_reg_offsets[ARC_NR_REGS] =
{
    22 * BYTES_IN_REGISTER,    /* r0       */
    21 * BYTES_IN_REGISTER,    /* r1       */
    20 * BYTES_IN_REGISTER,    /* r2       */
    19 * BYTES_IN_REGISTER,    /* r3       */
    18 * BYTES_IN_REGISTER,    /* r4       */
    17 * BYTES_IN_REGISTER,    /* r5       */
    16 * BYTES_IN_REGISTER,    /* r6       */
    15 * BYTES_IN_REGISTER,    /* r7       */
    14 * BYTES_IN_REGISTER,    /* r8       */
    13 * BYTES_IN_REGISTER,    /* r9       */
    12 * BYTES_IN_REGISTER,    /* r10      */
    11 * BYTES_IN_REGISTER,    /* r11      */
    10 * BYTES_IN_REGISTER,    /* r12      */
    39 * BYTES_IN_REGISTER,    /* r13      */
    38 * BYTES_IN_REGISTER,    /* r14      */
    37 * BYTES_IN_REGISTER,    /* r15      */
    36 * BYTES_IN_REGISTER,    /* r16      */
    35 * BYTES_IN_REGISTER,    /* r17      */
    34 * BYTES_IN_REGISTER,    /* r18      */
    33 * BYTES_IN_REGISTER,    /* r19      */
    32 * BYTES_IN_REGISTER,    /* r20      */
    31 * BYTES_IN_REGISTER,    /* r21      */
    30 * BYTES_IN_REGISTER,    /* r22      */
    29 * BYTES_IN_REGISTER,    /* r23      */
    28 * BYTES_IN_REGISTER,    /* r24      */
    27 * BYTES_IN_REGISTER,    /* r25      */
     9 * BYTES_IN_REGISTER,    /* r26      */
     1 * BYTES_IN_REGISTER,    /* bta      */
     2 * BYTES_IN_REGISTER,    /* lp_start */
     3 * BYTES_IN_REGISTER,    /* lp_end   */
     4 * BYTES_IN_REGISTER,    /* lp_count */
     5 * BYTES_IN_REGISTER,    /* status32 */
     7 * BYTES_IN_REGISTER,    /* blink    */
     8 * BYTES_IN_REGISTER,    /* fp       */
    25 * BYTES_IN_REGISTER,    /* sp       */
    REGISTER_NOT_PRESENT,      /* efa      */
     6 * BYTES_IN_REGISTER,    /* ret      */
    24 * BYTES_IN_REGISTER,    /* orig_r8  */
    40 * BYTES_IN_REGISTER,    /* stop_pc  */
};


/* -------------------------------------------------------------------------- */
/*                               forward declarations                         */
/* -------------------------------------------------------------------------- */

static int arc_linux_binutils_reg_to_regnum (struct gdbarch *gdbarch, int reg);


/* -------------------------------------------------------------------------- */
/*                               local macros                                 */
/* -------------------------------------------------------------------------- */

#define PRINT(regnum) \
    default_print_registers_info (gdbarch, file, frame, regnum, all)


/* -------------------------------------------------------------------------- */
/*                               local functions                              */
/* -------------------------------------------------------------------------- */

/* Returns TRUE if the instruction at PC is a branch (of any kind).
     *fall_thru is set to the address of the next insn.
     *target    is set to the branch target.  */

static Boolean
next_pc (CORE_ADDR pc, CORE_ADDR *fall_thru, CORE_ADDR *target)
{
    struct regcache        *regcache = get_current_regcache();
    struct disassemble_info di;
    struct arcDisState      instr;
    Boolean                 two_targets = FALSE;

    arc_initialize_disassembler(&di);

    /* So what is the instruction at the given PC?  */
    instr = arcAnalyzeInstr(pc, &di);

    /* By default, the next instruction is the one immediately after the one at PC.  */
    *fall_thru = pc + instr.instructionLen;

    DEBUG("--- next_pc(%x) = %x, isBranch = %d, tcnt = %d [%x], flow = %s (%d), "
          "reg for indirect jump = %d, nullifyMode = %s\n",
          (unsigned int) pc, (unsigned int) *fall_thru, instr.isBranch, instr.tcnt, instr.targets[0],
          (instr.flow == direct_jump || instr.flow == direct_call) ? "direct" : "indirect",
          instr.flow,
          instr.register_for_indirect_jump,
          ((instr.nullifyMode == (char) BR_exec_always) ? "delay slot" : "no delay"));

    /* OK, it's a branch.  */
    if ((Boolean) instr.isBranch)
    {
        two_targets = TRUE;

        /* If it's a direct jump or call, the destination address is encoded in
           the instruction, so we got it by disassembling the instruction;
           otherwise, it's an indirect jump to the address held in the register
           named in the instruction, so we must read that register.  */
        if (instr.flow == direct_jump || instr.flow == direct_call)
            *target = (CORE_ADDR) instr.targets[0];
        else
            regcache_cooked_read(regcache,
                                 arc_linux_binutils_reg_to_regnum(current_gdbarch,
                                 instr.register_for_indirect_jump),
                                 (gdb_byte*) target);

        /* For instructions with delay slots, the fall thru is not the instruction
           immediately after the branch instruction, but the one after that.  */
        if (instr.nullifyMode == (char) BR_exec_always)
        {
            struct arcDisState instr_d = arcAnalyzeInstr(*fall_thru, &di);

            *fall_thru += instr_d.instructionLen;
        }
    }


    /* Check for a zero-overhead loop.  */
    {
        unsigned int lp_end, lp_start, lp_count, status32;

        regcache_cooked_read(regcache, ARC_LP_START_REGNUM, (gdb_byte*) &lp_start);
        regcache_cooked_read(regcache, ARC_LP_END_REGNUM,   (gdb_byte*) &lp_end);
        regcache_cooked_read(regcache, ARC_LP_COUNT_REGNUM, (gdb_byte*) &lp_count);
        regcache_cooked_read(regcache, ARC_STATUS32_REGNUM, (gdb_byte*) &status32);

        if (!(status32 & STATUS32_L) && *fall_thru == lp_end && lp_count > 1)
        {
            /* The instruction is in effect a jump back to the start of the loop.  */
            two_targets = TRUE;
            *target     = lp_start;
        }
    }

    return two_targets;
}


/* Extract the register values found in the ABI GREGSET, storing their values in
   regcache.  */

static void
arcompact_linux_supply_gregset (struct regcache *regcache,
                                int              regnum,
                                const void      *gregs,
                                size_t           size)
{
    const bfd_byte *buf = gregs;
    unsigned int    reg;

    for (reg = 0; reg < ELEMENTS_IN_ARRAY(arcompact_linux_core_reg_offsets); reg++)
    {
        if (arcompact_linux_core_reg_offsets[reg] != REGISTER_NOT_PRESENT)
            regcache_raw_supply (regcache,
                                 (int) reg,
                                 buf + arcompact_linux_core_reg_offsets[reg]);
    }
}


/* Return whether the frame preceding next_frame corresponds to a GNU/Linux
   sigtramp routine.  */

static Boolean
is_linux_sigtramp (struct frame_info *next_frame)
{
    /* Find the PC for that previous frame.  */
    CORE_ADDR pc = frame_pc_unwind (next_frame);
    gdb_byte  buf[SIGTRAMP_INSNS_LENGTH];

    /* Read the memory at that PC (this gives us the code without any s/w
       breakpoints that may have been set in it).  */
    if (!safe_frame_unwind_memory (next_frame, pc, buf, (int) SIGTRAMP_INSNS_LENGTH))
        /* Failed to unwind frame.  */
        return FALSE;

    /* Is that code the sigtramp instruction sequence?  */
    if (memcmp(buf, arc_sigtramp_insns, SIGTRAMP_INSNS_LENGTH) == 0)
        return TRUE;

    /* No - look one instruction earlier in the code.  */
    if (!safe_frame_unwind_memory (next_frame, pc - 4, buf, (int) SIGTRAMP_INSNS_LENGTH))
        /* Failed to unwind frame.  */
        return FALSE;

    if (memcmp(buf, arc_sigtramp_insns, SIGTRAMP_INSNS_LENGTH) == 0)
        return TRUE;

    return FALSE;
}


/* Assuming next_frame is a frame following a GNU/Linux sigtramp
   routine, return the address of the associated sigcontext structure.  */

static CORE_ADDR
linux_sigcontext_addr (struct frame_info *next_frame)
{
    gdb_byte buf[4];

    frame_unwind_register (next_frame, ARC_SP_REGNUM, buf);

    return (CORE_ADDR) extract_unsigned_integer (buf, 4);
}


/* Determine whether the given register is a member of the given group.

   Returns 0, 1, or -1:
      0 means the register is not in the group.
      1 means the register is in the group.
     -1 means the tdep has nothing to say about this register and group.  */

static int
register_reggroup_p (int regnum, struct reggroup *group)
{
    if (system_reggroup)
    {
        if (regnum == ARC_ORIG_R8_REGNUM ||
            regnum == ARC_EFA_REGNUM     ||
            regnum == ARC_ERET_REGNUM    ||
            regnum == ARC_ERSTATUS_REGNUM)
            return 1;
    }
    else if (group == general_reggroup)
    {
        if (regnum == ARC_RET_REGNUM)
            return 0;

        return (regnum == ARC_STATUS32_REGNUM) ? 0 : 1;
    }

    /* Let the caller sort it out!  */
    return -1;
}


/* -------------------------------------------------------------------------- */
/*                       local functions called from gdb                      */
/* -------------------------------------------------------------------------- */

/* The Linux kernel stores only one of (ilink1, ilink2, eret). This is stored
   in the ret "register".  ilink1 is stored when the kernel has been entered
   because of a level 1 interrupt, etc.

   Same story for (status_l1, status_l2, erstatus).

   This disambiguity has been fixed by adding orig_r8 to pt_regs.

   FIXME: what is pt_regs????

   It will take the following values -
      1. if an exception of any kind occurs then orig_r8 >= 0
      2. Interrupt level 1 : orig == -1
      3. Interrupt level 2 : orig == -2

   Registers whose value we don't know are given the value zero.

   The only pseudo-registers are:

       ARC_ILINK1_REGNUM
       ARC_ILINK2_REGNUM
       ARC_ERET_REGNUM
       ARC_STATUS32_L1_REGNUM
       ARC_STATUS32_L2_REGNUM
       ARC_ERSTATUS_REGNUM
*/

static void
arc_linux_pseudo_register_read (struct gdbarch  *gdbarch,
                                struct regcache *regcache,
                                int              gdb_regno,
                                gdb_byte        *buf)
{
    unsigned int* contents = (unsigned int *) buf;
    unsigned int  status32, ret;
    int           orig_r8;

    regcache_cooked_read (regcache, ARC_ORIG_R8_REGNUM, (gdb_byte*) &orig_r8);

    if (gdb_regno == ARC_ILINK1_REGNUM ||
        gdb_regno == ARC_ILINK2_REGNUM ||
        gdb_regno == ARC_ERET_REGNUM)
    {
        regcache_cooked_read (regcache, ARC_RET_REGNUM, (gdb_byte*) &ret);

        if (gdb_regno == ARC_ILINK1_REGNUM)
            *contents = ((orig_r8 == -1) ? ret : 0);
        else if (gdb_regno == ARC_ILINK2_REGNUM)
            *contents = ((orig_r8 == -2) ? ret : 0);
        else  // (gdb_regno == ARC_ERET_REGNUM)
            *contents = ((orig_r8 >= 0)  ? ret : 0);

    }
    else if (gdb_regno == ARC_STATUS32_L1_REGNUM ||
             gdb_regno == ARC_STATUS32_L2_REGNUM ||
             gdb_regno == ARC_ERSTATUS_REGNUM)
    {
        regcache_cooked_read (regcache, ARC_STATUS32_REGNUM, (gdb_byte*) &status32);

        if (gdb_regno == ARC_STATUS32_L1_REGNUM)
            *contents = ((orig_r8 == -1) ? status32 : 0);
        else if (gdb_regno == ARC_STATUS32_L2_REGNUM)
            *contents = ((orig_r8 == -2) ? status32 : 0);
        else // (gdb_regno == ARC_ERSTATUS_REGNUM)
            *contents = ((orig_r8 >= 0)  ? status32 : 0);
    }
    else
        internal_error(__FILE__, __LINE__, _("%s: bad pseudo register number (%d)"), __FUNCTION__, gdb_regno);
}


static void
arc_linux_pseudo_register_write (struct gdbarch  *gdbarch,
                                 struct regcache *regcache,
                                 int              gdb_regno,
                                 const gdb_byte  *buf)
{
    /* None of our pseudo-regs are writable.  */
    internal_error(__FILE__, __LINE__, _("%s: pseudo-registers are unwritable"), __FUNCTION__);
}


/* Mapping from binutils/gcc register number to GDB register number ("regnum").
   N.B. registers such as ARC_FP_REGNUM, ARC_SP_REGNUM, etc., actually have
        different GDB register numbers in the arc-elf32 and arc-linux-uclibc
        configurations of the ARC gdb.  */

static int
arc_linux_binutils_reg_to_regnum (struct gdbarch *gdbarch, int reg)
{
    /* From gcc/config/arc/arc.h header file.  */

    if (reg >= 0 && reg <= 26)
        return reg;
    else if (reg == ARC_ABI_FRAME_POINTER)      /* fp */
        return ARC_FP_REGNUM;
    else if (reg == ARC_ABI_STACK_POINTER)      /* sp */
        return ARC_SP_REGNUM;
    else if (reg == 29)                         /* ilink1 */
        return ARC_ILINK1_REGNUM;
    else if (reg == 30)                         /* ilink2 */
        return ARC_ILINK2_REGNUM;
    else if (reg == 31)                         /* blink */
        return ARC_BLINK_REGNUM;
    else if (IS_EXTENSION_CORE_REGISTER(reg))   /* reserved */
        ;
    else if (reg == 60)                         /* lp_count */
        return ARC_LP_COUNT_REGNUM;
#if 0
    else if (reg == 61)                         /* reserved */
        ;
    else if (reg == 62)                         /* no such register */
        ;
   else if (reg == 63)                          /* PCL */
        ;
#endif

    warning(_("unmapped register #%d encountered"), reg);
    return -1;
}


/* Print the contents of one, some or all registers.

   Print registers in the correct order.
   Why not have the regnums in the right order in the first place?
   Because some of the registers have to be pseudo-registers because of
   the way the kernel is written, and because gdb assumes that
   pseudo-registers have regnums greater than real register regnums.  */

static void
arc_linux_print_registers_info (struct gdbarch    *gdbarch,
                                struct ui_file    *file,
                                struct frame_info *frame,
                                int                regnum,
                                int                all)
{
    if (regnum >= 0)
        PRINT (regnum);
    else /* If regnum < 0, print all registers.  */
    {
        int i;

        /* R0 .. R26 */
        for (i = 0; i <= 26; i++) PRINT (i);

        PRINT (ARC_FP_REGNUM        );
        PRINT (ARC_SP_REGNUM        );
        PRINT (ARC_ILINK1_REGNUM    );
        PRINT (ARC_ILINK2_REGNUM    );
        PRINT (ARC_BLINK_REGNUM     );
        PRINT (ARC_LP_COUNT_REGNUM  );

        /* Now the auxiliary registers.  */

        PRINT (ARC_BTA_REGNUM        );
        PRINT (ARC_LP_START_REGNUM   );
        PRINT (ARC_LP_END_REGNUM     );
        PRINT (ARC_EFA_REGNUM        );
        PRINT (ARC_ERET_REGNUM       );
        PRINT (ARC_STATUS32_L1_REGNUM);
        PRINT (ARC_STATUS32_L2_REGNUM);
        PRINT (ARC_ERSTATUS_REGNUM   );

        /* Show the PC.  */
        PRINT (ARC_STOP_PC_REGNUM    );
    }
}


/* Return the name of the given register.  */

static const char*
arc_linux_register_name (struct gdbarch *gdbarch, int gdb_regno)
{
    gdb_assert(ELEMENTS_IN_ARRAY(register_names) == (unsigned int) (ARC_NR_REGS + ARC_NR_PSEUDO_REGS));

    /* Oh, for a proper language with array bounds checking, like Ada...  */
    gdb_assert(0 <= gdb_regno && gdb_regno < (int) ELEMENTS_IN_ARRAY(register_names));

    return register_names[gdb_regno];
}


/* Determine whether the given register is read-only.  */

static int
arc_linux_cannot_store_register (struct gdbarch *gdbarch, int gdb_regno)
{
    if (gdb_regno == ARC_EFA_REGNUM         ||
        gdb_regno == ARC_ERET_REGNUM        ||
        gdb_regno == ARC_STATUS32_L1_REGNUM ||
        gdb_regno == ARC_STATUS32_L2_REGNUM ||
        gdb_regno == ARC_ERSTATUS_REGNUM    ||
        gdb_regno == ARC_ILINK1_REGNUM      ||
        gdb_regno == ARC_ILINK2_REGNUM)
    {
      /* No warning should be printed.  arc_cannot_store_register being
         called does not imply that someone is actually writing to regnum.  */

     /* warning(_("writing to read-only register: %s"), gdbarch_register_name(gdbarch, gdb_regno)); */
        return 1;
    }

    return 0;
}


/* This function is called just before we resume executing the inferior, if we
   want to single-step it.  We find the target(s) of the instruction about to
   be executed and and place breakpoints there.  */

static int
arc_linux_software_single_step (struct frame_info *frame)
{
    CORE_ADDR fall_thru, branch_target;
    CORE_ADDR pc              = get_frame_pc(frame);
    Boolean   two_breakpoints = next_pc(pc, &fall_thru, &branch_target);

    insert_single_step_breakpoint (fall_thru);

    if (two_breakpoints)
    {
       if (pc != branch_target)
           insert_single_step_breakpoint (branch_target);
    }

    /* Always returns true for now.  */
    return 1;
}


/* Set the program counter for process PTID to PC.  */

static void
arc_linux_write_pc (struct regcache *regcache, CORE_ADDR pc)
{
    regcache_cooked_write_unsigned (regcache, ARC_PC_REGNUM, pc);

    /* We must be careful with modifying the program counter.  If we
       just interrupted a system call, the kernel might try to restart
       it when we resume the inferior.  On restarting the system call,
       the kernel will try backing up the program counter even though it
       no longer points at the system call.  This typically results in a
       SIGSEGV or SIGILL.  We can prevent this by writing `-1' in the
       "orig_r8" pseudo-register.

       Note that "orig_r8" is saved when setting up a dummy call frame.
       This means that it is properly restored when that frame is
       popped, and that the interrupted system call will be restarted
       when we resume the inferior on return from a function call from
       within GDB.  In all other cases the system call will not be
       restarted.  */

    // FIXME: why -3 and not -1? -3 does not appear to be a defined valued for
    //        orig_r8 (i.e. -2, -1 or >= 0) - perhaps it means "none of these"?
    regcache_cooked_write_signed (regcache, ARC_ORIG_R8_REGNUM, -3);
}


/* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.

   This is called on every single step through the PLT and runtime resolver.

   This function:
      1) decides whether a PLT has sent us into the linker to resolve
         a function reference, and
      2) if so, tells us where to set a temporary breakpoint that will
         trigger when the dynamic linker is done.  */

static CORE_ADDR
arc_linux_skip_solib_resolver (struct gdbarch *gdbarch, CORE_ADDR pc)
{
    /* For uClibc 0.9.26.

         An unresolved PLT entry points to "__dl_linux_resolve", which calls
         "__dl_linux_resolver" to do the resolving and then eventually jumps to
         the function.

         So we look for the symbol `_dl_linux_resolver', and if we are there,
         gdb sets a breakpoint at the return address, and continues.  */

    /* Lookup_minimal_symbol didn't work, for some reason.  */
    struct symbol *resolver =
                   lookup_symbol_global ("_dl_linux_resolver", 0, 0, VAR_DOMAIN, 0);

    DEBUG((resolver == NULL) ? "--- %s : pc = %x, no resolver found"
                             : "--- %s : pc = %x, resolver at %x\n",
          __FUNCTION__,
          (unsigned int) pc,
          (unsigned int) ((resolver == NULL) ? 0 : BLOCK_START (SYMBOL_BLOCK_VALUE (resolver))));

    if ((resolver != NULL) && (BLOCK_START (SYMBOL_BLOCK_VALUE (resolver))) == pc)
        /* Find the return address.  */
        return frame_pc_unwind (get_current_frame ());

    /* No breakpoint is required.  */
    return 0;
}


/* Call the right architecture variant's supply_gregset function.  For now, we
   have only ARCompact.  */

static void
arc_linux_supply_gregset (const struct regset *regset,
                          struct regcache     *regcache,
                          int                  regnum,
                          const void          *gregs,
                          size_t               size)
{
    arcompact_linux_supply_gregset (regcache, regnum, gregs, size);
}


/* Functions for handling core files.
   The first element is a parameter to pass the rest of the functions.  We
   don't need it.
   supply_gregset is for reading the core file.
   collect_regset, which we haven't defined, would be for writing the core
   file.  */

static const struct regset *
arc_linux_regset_from_core_section (struct gdbarch *core_arch,
                                    const char     *sect_name,
                                    size_t          sect_size)
{
    static const struct regset arc_linux_gregset =
    {
        NULL,                        // descr
        arc_linux_supply_gregset,    // supply_regset
        NULL,                        // collect_regset
        NULL                         // arch
    };

    if (strcmp (sect_name, ".reg") == 0)
        return &arc_linux_gregset;

    return NULL;
}


/* Initialize for this ABI.  */

static void
arc_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
    struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

    /* Fill in target-dependent info in ARC-private structure.  */

    tdep->is_sigtramp             = is_linux_sigtramp;
    tdep->sigcontext_addr         = linux_sigcontext_addr;
    tdep->sc_reg_offset           = arc_linux_sc_reg_offset;
    tdep->sc_num_regs             = ELEMENTS_IN_ARRAY(arc_linux_sc_reg_offset);
    tdep->pc_regnum_in_sigcontext = ARC_RET_REGNUM;

    tdep->le_breakpoint_instruction = le_breakpoint_instruction;
    tdep->be_breakpoint_instruction = be_breakpoint_instruction;
    tdep->breakpoint_size        = (unsigned int) sizeof(le_breakpoint_instruction);

    tdep->register_reggroup_p = register_reggroup_p;

    tdep->lowest_pc              = 0x74;             // FIXME: why this?
    tdep->processor_variant_info = NULL;

    /* Pass target-dependent info to gdb.  */

    /* ARC_NR_REGS and ARC_NR_PSEUDO_REGS are defined in the tm.h configuration file.  */
    set_gdbarch_pc_regnum                (gdbarch, ARC_STOP_PC_REGNUM);
    set_gdbarch_num_regs                 (gdbarch, ARC_NR_REGS);
    set_gdbarch_num_pseudo_regs          (gdbarch, ARC_NR_PSEUDO_REGS);
    set_gdbarch_print_registers_info     (gdbarch, arc_linux_print_registers_info);
    set_gdbarch_register_name            (gdbarch, arc_linux_register_name);
    set_gdbarch_cannot_store_register    (gdbarch, arc_linux_cannot_store_register);
    set_gdbarch_dwarf2_reg_to_regnum     (gdbarch, arc_linux_binutils_reg_to_regnum);

    set_gdbarch_decr_pc_after_break      (gdbarch, 0);
    set_gdbarch_software_single_step     (gdbarch, arc_linux_software_single_step);
    set_gdbarch_write_pc                 (gdbarch, arc_linux_write_pc);
    set_gdbarch_pseudo_register_read     (gdbarch, arc_linux_pseudo_register_read);
    set_gdbarch_pseudo_register_write    (gdbarch, arc_linux_pseudo_register_write);
    set_gdbarch_regset_from_core_section (gdbarch, arc_linux_regset_from_core_section);
    set_gdbarch_skip_solib_resolver      (gdbarch, arc_linux_skip_solib_resolver);

    /* GNU/Linux uses SVR4-style shared libraries.  */
    set_solib_svr4_fetch_link_map_offsets (gdbarch, svr4_ilp32_fetch_link_map_offsets);
}


/* -------------------------------------------------------------------------- */
/*                               externally visible functions                 */
/* -------------------------------------------------------------------------- */

/* Initialize the module. This function is called from the gdb core on start-up.  */

void
_initialize_arc_linux_tdep (void)
{
    /* Register a handler with gdb for the Linux O/S ABI variant for the ARC
       processor architecture, providing an initialization function;
       'bfd_arch_arc' is an enumeration value specifically denoting the ARC
       architecture.  */
    gdbarch_register_osabi (bfd_arch_arc,
                            0,                   // machine (irrelevant)
                            GDB_OSABI_LINUX,
                            arc_linux_init_abi);
}


/* This function is required simply to avoid an undefined symbol at linkage.  */

void
arc_check_pc_defined (struct gdbarch *gdbarch)
{
}

/******************************************************************************/