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/* GNU/Linux on ARM target support.

   Copyright 1999, 2000, 2001, 2002 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 "target.h"

#include "value.h"

#include "gdbtypes.h"

#include "floatformat.h"

#include "gdbcore.h"

#include "frame.h"

#include "regcache.h"

#include "doublest.h"

#include "arm-tdep.h"

/* For shared library handling.  */

#include "symtab.h"

#include "symfile.h"

#include "objfiles.h"

/* Under ARM GNU/Linux the traditional way of performing a breakpoint

   is to execute a particular software interrupt, rather than use a

   particular undefined instruction to provoke a trap.  Upon exection

   of the software interrupt the kernel stops the inferior with a

   SIGTRAP, and wakes the debugger.  Since ARM GNU/Linux is little

   endian, and doesn't support Thumb at the moment we only override

   the ARM little-endian breakpoint.  */

static const char arm_linux_arm_le_breakpoint[] = {0x01,0x00,0x9f,0xef};

/* CALL_DUMMY_WORDS:

   This sequence of words is the instructions

   mov  lr, pc

   mov  pc, r4

   swi  bkpt_swi

   Note this is 12 bytes.  */

LONGEST arm_linux_call_dummy_words[] =

{

  0xe1a0e00f, 0xe1a0f004, 0xef9f001

};

/* Description of the longjmp buffer.  */

#define ARM_LINUX_JB_ELEMENT_SIZE       INT_REGISTER_RAW_SIZE

#define ARM_LINUX_JB_PC                 21

/* 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.  */

/* FIXME rearnsha/2002-02-23: This function shouldn't be necessary.

   The ARM generic one should be able to handle the model used by

   linux and the low-level formatting of the registers should be

   hidden behind the regcache abstraction.  */

static 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 GNU/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))

                ? ARM_F0_REGNUM : ARM_A1_REGNUM);

  memcpy (valbuf, &regbuf[REGISTER_BYTE (regnum)], TYPE_LENGTH (type));

}

/* Note: ScottB

   This function does not support passing parameters using the FPA

   variant of the APCS.  It passes any floating point arguments in the

   general registers and/or on the stack.

   FIXME:  This and arm_push_arguments should be merged.  However this

           function breaks on a little endian host, big endian target

           using the COFF file format.  ELF is ok.

           ScottB.  */

/* Addresses for calling Thumb functions have the bit 0 set.

   Here are some macros to test, set, or clear bit 0 of addresses.  */

#define IS_THUMB_ADDR(addr)     ((addr) & 1)

#define MAKE_THUMB_ADDR(addr)   ((addr) | 1)

#define UNMAKE_THUMB_ADDR(addr) ((addr) & ~1)

static CORE_ADDR

arm_linux_push_arguments (int nargs, struct value **args, CORE_ADDR sp,

                          int struct_return, CORE_ADDR struct_addr)

{

  char *fp;

  int argnum, argreg, nstack_size;

  /* Walk through the list of args and determine how large a temporary

     stack is required.  Need to take care here as structs may be

     passed on the stack, and we have to to push them.  */

  nstack_size = -4 * REGISTER_SIZE;     /* Some arguments go into A1-A4.  */

  if (struct_return)                    /* The struct address goes in A1.  */

    nstack_size += REGISTER_SIZE;

  /* Walk through the arguments and add their size to nstack_size.  */

  for (argnum = 0; argnum < nargs; argnum++)

    {

      int len;

      struct type *arg_type;

      arg_type = check_typedef (VALUE_TYPE (args[argnum]));

      len = TYPE_LENGTH (arg_type);

      /* ANSI C code passes float arguments as integers, K&R code

         passes float arguments as doubles.  Correct for this here.  */

      if (TYPE_CODE_FLT == TYPE_CODE (arg_type) && REGISTER_SIZE == len)

        nstack_size += FP_REGISTER_VIRTUAL_SIZE;

      else

        nstack_size += len;

    }

  /* Allocate room on the stack, and initialize our stack frame

     pointer.  */

  fp = NULL;

  if (nstack_size > 0)

    {

      sp -= nstack_size;

      fp = (char *) sp;

    }

  /* Initialize the integer argument register pointer.  */

  argreg = ARM_A1_REGNUM;

  /* The struct_return pointer occupies the first parameter passing

     register.  */

  if (struct_return)

    write_register (argreg++, struct_addr);

  /* Process arguments from left to right.  Store as many as allowed

     in the parameter passing registers (A1-A4), and save the rest on

     the temporary stack.  */

  for (argnum = 0; argnum < nargs; argnum++)

    {

      int len;

      char *val;

      CORE_ADDR regval;

      enum type_code typecode;

      struct type *arg_type, *target_type;

      arg_type = check_typedef (VALUE_TYPE (args[argnum]));

      target_type = TYPE_TARGET_TYPE (arg_type);

      len = TYPE_LENGTH (arg_type);

      typecode = TYPE_CODE (arg_type);

      val = (char *) VALUE_CONTENTS (args[argnum]);

      /* ANSI C code passes float arguments as integers, K&R code

         passes float arguments as doubles.  The .stabs record for

         for ANSI prototype floating point arguments records the

         type as FP_INTEGER, while a K&R style (no prototype)

         .stabs records the type as FP_FLOAT.  In this latter case

         the compiler converts the float arguments to double before

         calling the function.  */

      if (TYPE_CODE_FLT == typecode && REGISTER_SIZE == len)

        {

          DOUBLEST dblval;

          dblval = extract_floating (val, len);

          len = TARGET_DOUBLE_BIT / TARGET_CHAR_BIT;

          val = alloca (len);

          store_floating (val, len, dblval);

        }

      /* If the argument is a pointer to a function, and it is a Thumb

         function, set the low bit of the pointer.  */

      if (TYPE_CODE_PTR == typecode

          && NULL != target_type

          && TYPE_CODE_FUNC == TYPE_CODE (target_type))

        {

          CORE_ADDR regval = extract_address (val, len);

          if (arm_pc_is_thumb (regval))

            store_address (val, len, MAKE_THUMB_ADDR (regval));

        }

      /* Copy the argument to general registers or the stack in

         register-sized pieces.  Large arguments are split between

         registers and stack.  */

      while (len > 0)

        {

          int partial_len = len < REGISTER_SIZE ? len : REGISTER_SIZE;

          if (argreg <= ARM_LAST_ARG_REGNUM)

            {

              /* It's an argument being passed in a general register.  */

              regval = extract_address (val, partial_len);

              write_register (argreg++, regval);

            }

          else

            {

              /* Push the arguments onto the stack.  */

              write_memory ((CORE_ADDR) fp, val, REGISTER_SIZE);

              fp += REGISTER_SIZE;

            }

          len -= partial_len;

          val += partial_len;

        }

    }

  /* Return adjusted stack pointer.  */

  return sp;

}

/*

   Dynamic Linking on ARM GNU/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 GNU/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].  */

/* Find the minimal symbol named NAME, and return both the minsym

   struct and its objfile.  This probably ought to be in minsym.c, but

   everything there is trying to deal with things like C++ and

   SOFUN_ADDRESS_MAYBE_TURQUOISE, ...  Since this is so simple, it may

   be considered too special-purpose for general consumption.  */

static struct minimal_symbol *

find_minsym_and_objfile (char *name, struct objfile **objfile_p)

{

  struct objfile *objfile;

  ALL_OBJFILES (objfile)

    {

      struct minimal_symbol *msym;

      ALL_OBJFILE_MSYMBOLS (objfile, msym)

        {

          if (SYMBOL_NAME (msym)

              && strcmp (SYMBOL_NAME (msym), name) == 0)

            {

              *objfile_p = objfile;

              return msym;

            }

        }

    }

  return 0;

}

static CORE_ADDR

skip_hurd_resolver (CORE_ADDR pc)

{

  /* The HURD dynamic linker is part of the GNU C library, so many

     GNU/Linux distributions use it.  (All ELF versions, as far as I

     know.)  An unresolved PLT entry points to "_dl_runtime_resolve",

     which calls "fixup" to patch the PLT, and then passes control to

     the function.

     We look for the symbol `_dl_runtime_resolve', and find `fixup' in

     the same objfile.  If we are at the entry point of `fixup', then

     we set a breakpoint at the return address (at the top of the

     stack), and continue.

     It's kind of gross to do all these checks every time we're

     called, since they don't change once the executable has gotten

     started.  But this is only a temporary hack --- upcoming versions

     of GNU/Linux will provide a portable, efficient interface for

     debugging programs that use shared libraries.  */

  struct objfile *objfile;

  struct minimal_symbol *resolver

    = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile);

  if (resolver)

    {

      struct minimal_symbol *fixup

        = lookup_minimal_symbol ("fixup", NULL, objfile);

      if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc)

        return (SAVED_PC_AFTER_CALL (get_current_frame ()));

    }

  return 0;

}

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

   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.  */

CORE_ADDR

arm_linux_skip_solib_resolver (CORE_ADDR pc)

{

  CORE_ADDR result;

  /* Plug in functions for other kinds of resolvers here.  */

  result = skip_hurd_resolver (pc);

  if (result)

    return result;

  return 0;

}

/* The constants below were determined by examining the following files

   in the linux kernel sources:

      arch/arm/kernel/signal.c

          - see SWI_SYS_SIGRETURN and SWI_SYS_RT_SIGRETURN

      include/asm-arm/unistd.h

          - see __NR_sigreturn, __NR_rt_sigreturn, and __NR_SYSCALL_BASE */

#define ARM_LINUX_SIGRETURN_INSTR       0xef900077

#define ARM_LINUX_RT_SIGRETURN_INSTR    0xef9000ad

/* arm_linux_in_sigtramp determines if PC points at one of the

   instructions which cause control to return to the Linux kernel upon

   return from a signal handler.  FUNC_NAME is unused.  */

int

arm_linux_in_sigtramp (CORE_ADDR pc, char *func_name)

{

  unsigned long inst;

  inst = read_memory_integer (pc, 4);

  return (inst == ARM_LINUX_SIGRETURN_INSTR

          || inst == ARM_LINUX_RT_SIGRETURN_INSTR);

}

/* arm_linux_sigcontext_register_address returns the address in the

   sigcontext of register REGNO given a stack pointer value SP and

   program counter value PC.  The value 0 is returned if PC is not

   pointing at one of the signal return instructions or if REGNO is

   not saved in the sigcontext struct.  */

CORE_ADDR

arm_linux_sigcontext_register_address (CORE_ADDR sp, CORE_ADDR pc, int regno)

{

  unsigned long inst;

  CORE_ADDR reg_addr = 0;

  inst = read_memory_integer (pc, 4);

  if (inst == ARM_LINUX_SIGRETURN_INSTR

      || inst == ARM_LINUX_RT_SIGRETURN_INSTR)

    {

      CORE_ADDR sigcontext_addr;

      /* The sigcontext structure is at different places for the two

         signal return instructions.  For ARM_LINUX_SIGRETURN_INSTR,

         it starts at the SP value.  For ARM_LINUX_RT_SIGRETURN_INSTR,

         it is at SP+8.  For the latter instruction, it may also be

         the case that the address of this structure may be determined

         by reading the 4 bytes at SP, but I'm not convinced this is

         reliable.

         In any event, these magic constants (0 and 8) may be

         determined by examining struct sigframe and struct

         rt_sigframe in arch/arm/kernel/signal.c in the Linux kernel

         sources.  */

      if (inst == ARM_LINUX_RT_SIGRETURN_INSTR)

        sigcontext_addr = sp + 8;

      else /* inst == ARM_LINUX_SIGRETURN_INSTR */

        sigcontext_addr = sp + 0;

      /* The layout of the sigcontext structure for ARM GNU/Linux is

         in include/asm-arm/sigcontext.h in the Linux kernel sources.

         There are three 4-byte fields which precede the saved r0

         field.  (This accounts for the 12 in the code below.)  The

         sixteen registers (4 bytes per field) follow in order.  The

         PSR value follows the sixteen registers which accounts for

         the constant 19 below. */

      if (0 <= regno && regno <= ARM_PC_REGNUM)

        reg_addr = sigcontext_addr + 12 + (4 * regno);

      else if (regno == ARM_PS_REGNUM)

        reg_addr = sigcontext_addr + 19 * 4;

    }

  return reg_addr;

}

static void

arm_linux_init_abi (struct gdbarch_info info,

                    struct gdbarch *gdbarch)

{

  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

  tdep->lowest_pc = 0x8000;

  tdep->arm_breakpoint = arm_linux_arm_le_breakpoint;

  tdep->arm_breakpoint_size = sizeof (arm_linux_arm_le_breakpoint);

  tdep->jb_pc = ARM_LINUX_JB_PC;

  tdep->jb_elt_size = ARM_LINUX_JB_ELEMENT_SIZE;

  set_gdbarch_call_dummy_words (gdbarch, arm_linux_call_dummy_words);

  set_gdbarch_sizeof_call_dummy_words (gdbarch,

                                       sizeof (arm_linux_call_dummy_words));

  /* The following two overrides shouldn't be needed.  */

  set_gdbarch_deprecated_extract_return_value (gdbarch, arm_linux_extract_return_value);

  set_gdbarch_push_arguments (gdbarch, arm_linux_push_arguments);

  /* Shared library handling.  */

  set_gdbarch_in_solib_call_trampoline (gdbarch, in_plt_section);

  set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);

}

void

_initialize_arm_linux_tdep (void)

{

  gdbarch_register_osabi (bfd_arch_arm, GDB_OSABI_LINUX, arm_linux_init_abi);

}