gdb/arm-linux-tdep.c

   1 /* GNU/Linux on ARM target support.
   2    Copyright 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software
  18    Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include "defs.h"
  22 #include "target.h"
  23 #include "value.h"
  24 #include "gdbtypes.h"
  25 #include "floatformat.h"
  26 #include "gdbcore.h"
  27 #include "frame.h"
  28 #include "regcache.h"
  29 #include "doublest.h"
  30 #include "solib-svr4.h"
  31 #include "osabi.h"
  32
  33 #include "arm-tdep.h"
  34 #include "glibc-tdep.h"
  35
  36 /* Under ARM GNU/Linux the traditional way of performing a breakpoint
  37    is to execute a particular software interrupt, rather than use a
  38    particular undefined instruction to provoke a trap.  Upon exection
  39    of the software interrupt the kernel stops the inferior with a
  40    SIGTRAP, and wakes the debugger.  Since ARM GNU/Linux doesn't support
  41    Thumb at the moment we only override the ARM breakpoints.  */
  42
  43 static const char arm_linux_arm_le_breakpoint[] = { 0x01, 0x00, 0x9f, 0xef };
  44
  45 static const char arm_linux_arm_be_breakpoint[] = { 0xef, 0x9f, 0x00, 0x01 };
  46
  47 /* DEPRECATED_CALL_DUMMY_WORDS:
  48    This sequence of words is the instructions
  49
  50    mov  lr, pc
  51    mov  pc, r4
  52    swi  bkpt_swi
  53
  54    Note this is 12 bytes.  */
  55
  56 LONGEST arm_linux_call_dummy_words[] =
  57 {
  58   0xe1a0e00f, 0xe1a0f004, 0xef9f001
  59 };
  60
  61 /* Description of the longjmp buffer.  */
  62 #define ARM_LINUX_JB_ELEMENT_SIZE       INT_REGISTER_RAW_SIZE
  63 #define ARM_LINUX_JB_PC                 21
  64
  65 /* Extract from an array REGBUF containing the (raw) register state
  66    a function return value of type TYPE, and copy that, in virtual format,
  67    into VALBUF.  */
  68 /* FIXME rearnsha/2002-02-23: This function shouldn't be necessary.
  69    The ARM generic one should be able to handle the model used by
  70    linux and the low-level formatting of the registers should be
  71    hidden behind the regcache abstraction.  */
  72 static void
  73 arm_linux_extract_return_value (struct type *type,
  74                                 char regbuf[],
  75                                 char *valbuf)
  76 {
  77   /* ScottB: This needs to be looked at to handle the different
  78      floating point emulators on ARM GNU/Linux.  Right now the code
  79      assumes that fetch inferior registers does the right thing for
  80      GDB.  I suspect this won't handle NWFPE registers correctly, nor
  81      will the default ARM version (arm_extract_return_value()).  */
  82
  83   int regnum = ((TYPE_CODE_FLT == TYPE_CODE (type))
  84                 ? ARM_F0_REGNUM : ARM_A1_REGNUM);
  85   memcpy (valbuf, &regbuf[DEPRECATED_REGISTER_BYTE (regnum)], TYPE_LENGTH (type));
  86 }
  87
  88 /* Note: ScottB
  89
  90    This function does not support passing parameters using the FPA
  91    variant of the APCS.  It passes any floating point arguments in the
  92    general registers and/or on the stack.
  93
  94    FIXME:  This and arm_push_arguments should be merged.  However this
  95            function breaks on a little endian host, big endian target
  96            using the COFF file format.  ELF is ok.
  97
  98            ScottB.  */
  99
 100 /* Addresses for calling Thumb functions have the bit 0 set.
 101    Here are some macros to test, set, or clear bit 0 of addresses.  */
 102 #define IS_THUMB_ADDR(addr)     ((addr) & 1)
 103 #define MAKE_THUMB_ADDR(addr)   ((addr) | 1)
 104 #define UNMAKE_THUMB_ADDR(addr) ((addr) & ~1)
 105
 106 static CORE_ADDR
 107 arm_linux_push_arguments (int nargs, struct value **args, CORE_ADDR sp,
 108                           int struct_return, CORE_ADDR struct_addr)
 109 {
 110   char *fp;
 111   int argnum, argreg, nstack_size;
 112
 113   /* Walk through the list of args and determine how large a temporary
 114      stack is required.  Need to take care here as structs may be
 115      passed on the stack, and we have to to push them.  */
 116   nstack_size = -4 * DEPRECATED_REGISTER_SIZE;  /* Some arguments go into A1-A4.  */
 117
 118   if (struct_return)                    /* The struct address goes in A1.  */
 119     nstack_size += DEPRECATED_REGISTER_SIZE;
 120
 121   /* Walk through the arguments and add their size to nstack_size.  */
 122   for (argnum = 0; argnum < nargs; argnum++)
 123     {
 124       int len;
 125       struct type *arg_type;
 126
 127       arg_type = check_typedef (VALUE_TYPE (args[argnum]));
 128       len = TYPE_LENGTH (arg_type);
 129
 130       /* ANSI C code passes float arguments as integers, K&R code
 131          passes float arguments as doubles.  Correct for this here.  */
 132       if (TYPE_CODE_FLT == TYPE_CODE (arg_type) && DEPRECATED_REGISTER_SIZE == len)
 133         nstack_size += FP_REGISTER_VIRTUAL_SIZE;
 134       else
 135         nstack_size += len;
 136     }
 137
 138   /* Allocate room on the stack, and initialize our stack frame
 139      pointer.  */
 140   fp = NULL;
 141   if (nstack_size > 0)
 142     {
 143       sp -= nstack_size;
 144       fp = (char *) sp;
 145     }
 146
 147   /* Initialize the integer argument register pointer.  */
 148   argreg = ARM_A1_REGNUM;
 149
 150   /* The struct_return pointer occupies the first parameter passing
 151      register.  */
 152   if (struct_return)
 153     write_register (argreg++, struct_addr);
 154
 155   /* Process arguments from left to right.  Store as many as allowed
 156      in the parameter passing registers (A1-A4), and save the rest on
 157      the temporary stack.  */
 158   for (argnum = 0; argnum < nargs; argnum++)
 159     {
 160       int len;
 161       char *val;
 162       CORE_ADDR regval;
 163       enum type_code typecode;
 164       struct type *arg_type, *target_type;
 165
 166       arg_type = check_typedef (VALUE_TYPE (args[argnum]));
 167       target_type = TYPE_TARGET_TYPE (arg_type);
 168       len = TYPE_LENGTH (arg_type);
 169       typecode = TYPE_CODE (arg_type);
 170       val = (char *) VALUE_CONTENTS (args[argnum]);
 171
 172       /* ANSI C code passes float arguments as integers, K&R code
 173          passes float arguments as doubles.  The .stabs record for
 174          for ANSI prototype floating point arguments records the
 175          type as FP_INTEGER, while a K&R style (no prototype)
 176          .stabs records the type as FP_FLOAT.  In this latter case
 177          the compiler converts the float arguments to double before
 178          calling the function.  */
 179       if (TYPE_CODE_FLT == typecode && DEPRECATED_REGISTER_SIZE == len)
 180         {
 181           DOUBLEST dblval;
 182           dblval = deprecated_extract_floating (val, len);
 183           len = TARGET_DOUBLE_BIT / TARGET_CHAR_BIT;
 184           val = alloca (len);
 185           deprecated_store_floating (val, len, dblval);
 186         }
 187
 188       /* If the argument is a pointer to a function, and it is a Thumb
 189          function, set the low bit of the pointer.  */
 190       if (TYPE_CODE_PTR == typecode
 191           && NULL != target_type
 192           && TYPE_CODE_FUNC == TYPE_CODE (target_type))
 193         {
 194           CORE_ADDR regval = extract_unsigned_integer (val, len);
 195           if (arm_pc_is_thumb (regval))
 196             store_unsigned_integer (val, len, MAKE_THUMB_ADDR (regval));
 197         }
 198
 199       /* Copy the argument to general registers or the stack in
 200          register-sized pieces.  Large arguments are split between
 201          registers and stack.  */
 202       while (len > 0)
 203         {
 204           int partial_len = len < DEPRECATED_REGISTER_SIZE ? len : DEPRECATED_REGISTER_SIZE;
 205
 206           if (argreg <= ARM_LAST_ARG_REGNUM)
 207             {
 208               /* It's an argument being passed in a general register.  */
 209               regval = extract_unsigned_integer (val, partial_len);
 210               write_register (argreg++, regval);
 211             }
 212           else
 213             {
 214               /* Push the arguments onto the stack.  */
 215               write_memory ((CORE_ADDR) fp, val, DEPRECATED_REGISTER_SIZE);
 216               fp += DEPRECATED_REGISTER_SIZE;
 217             }
 218
 219           len -= partial_len;
 220           val += partial_len;
 221         }
 222     }
 223
 224   /* Return adjusted stack pointer.  */
 225   return sp;
 226 }
 227
 228 /*
 229    Dynamic Linking on ARM GNU/Linux
 230    --------------------------------
 231
 232    Note: PLT = procedure linkage table
 233    GOT = global offset table
 234
 235    As much as possible, ELF dynamic linking defers the resolution of
 236    jump/call addresses until the last minute. The technique used is
 237    inspired by the i386 ELF design, and is based on the following
 238    constraints.
 239
 240    1) The calling technique should not force a change in the assembly
 241    code produced for apps; it MAY cause changes in the way assembly
 242    code is produced for position independent code (i.e. shared
 243    libraries).
 244
 245    2) The technique must be such that all executable areas must not be
 246    modified; and any modified areas must not be executed.
 247
 248    To do this, there are three steps involved in a typical jump:
 249
 250    1) in the code
 251    2) through the PLT
 252    3) using a pointer from the GOT
 253
 254    When the executable or library is first loaded, each GOT entry is
 255    initialized to point to the code which implements dynamic name
 256    resolution and code finding.  This is normally a function in the
 257    program interpreter (on ARM GNU/Linux this is usually
 258    ld-linux.so.2, but it does not have to be).  On the first
 259    invocation, the function is located and the GOT entry is replaced
 260    with the real function address.  Subsequent calls go through steps
 261    1, 2 and 3 and end up calling the real code.
 262
 263    1) In the code:
 264
 265    b    function_call
 266    bl   function_call
 267
 268    This is typical ARM code using the 26 bit relative branch or branch
 269    and link instructions.  The target of the instruction
 270    (function_call is usually the address of the function to be called.
 271    In position independent code, the target of the instruction is
 272    actually an entry in the PLT when calling functions in a shared
 273    library.  Note that this call is identical to a normal function
 274    call, only the target differs.
 275
 276    2) In the PLT:
 277
 278    The PLT is a synthetic area, created by the linker. It exists in
 279    both executables and libraries. It is an array of stubs, one per
 280    imported function call. It looks like this:
 281
 282    PLT[0]:
 283    str     lr, [sp, #-4]!       @push the return address (lr)
 284    ldr     lr, [pc, #16]   @load from 6 words ahead
 285    add     lr, pc, lr      @form an address for GOT[0]
 286    ldr     pc, [lr, #8]!   @jump to the contents of that addr
 287
 288    The return address (lr) is pushed on the stack and used for
 289    calculations.  The load on the second line loads the lr with
 290    &GOT[3] - . - 20.  The addition on the third leaves:
 291
 292    lr = (&GOT[3] - . - 20) + (. + 8)
 293    lr = (&GOT[3] - 12)
 294    lr = &GOT[0]
 295
 296    On the fourth line, the pc and lr are both updated, so that:
 297
 298    pc = GOT[2]
 299    lr = &GOT[0] + 8
 300    = &GOT[2]
 301
 302    NOTE: PLT[0] borrows an offset .word from PLT[1]. This is a little
 303    "tight", but allows us to keep all the PLT entries the same size.
 304
 305    PLT[n+1]:
 306    ldr     ip, [pc, #4]    @load offset from gotoff
 307    add     ip, pc, ip      @add the offset to the pc
 308    ldr     pc, [ip]        @jump to that address
 309    gotoff: .word   GOT[n+3] - .
 310
 311    The load on the first line, gets an offset from the fourth word of
 312    the PLT entry.  The add on the second line makes ip = &GOT[n+3],
 313    which contains either a pointer to PLT[0] (the fixup trampoline) or
 314    a pointer to the actual code.
 315
 316    3) In the GOT:
 317
 318    The GOT contains helper pointers for both code (PLT) fixups and
 319    data fixups.  The first 3 entries of the GOT are special. The next
 320    M entries (where M is the number of entries in the PLT) belong to
 321    the PLT fixups. The next D (all remaining) entries belong to
 322    various data fixups. The actual size of the GOT is 3 + M + D.
 323
 324    The GOT is also a synthetic area, created by the linker. It exists
 325    in both executables and libraries.  When the GOT is first
 326    initialized , all the GOT entries relating to PLT fixups are
 327    pointing to code back at PLT[0].
 328
 329    The special entries in the GOT are:
 330
 331    GOT[0] = linked list pointer used by the dynamic loader
 332    GOT[1] = pointer to the reloc table for this module
 333    GOT[2] = pointer to the fixup/resolver code
 334
 335    The first invocation of function call comes through and uses the
 336    fixup/resolver code.  On the entry to the fixup/resolver code:
 337
 338    ip = &GOT[n+3]
 339    lr = &GOT[2]
 340    stack[0] = return address (lr) of the function call
 341    [r0, r1, r2, r3] are still the arguments to the function call
 342
 343    This is enough information for the fixup/resolver code to work
 344    with.  Before the fixup/resolver code returns, it actually calls
 345    the requested function and repairs &GOT[n+3].  */
 346
 347 /* Fetch, and possibly build, an appropriate link_map_offsets structure
 348    for ARM linux targets using the struct offsets defined in <link.h>.
 349    Note, however, that link.h is not actually referred to in this file.
 350    Instead, the relevant structs offsets were obtained from examining
 351    link.h.  (We can't refer to link.h from this file because the host
 352    system won't necessarily have it, or if it does, the structs which
 353    it defines will refer to the host system, not the target).  */
 354
 355 static struct link_map_offsets *
 356 arm_linux_svr4_fetch_link_map_offsets (void)
 357 {
 358   static struct link_map_offsets lmo;
 359   static struct link_map_offsets *lmp = 0;
 360
 361   if (lmp == 0)
 362     {
 363       lmp = &lmo;
 364
 365       lmo.r_debug_size = 8;     /* Actual size is 20, but this is all we
 366                                    need.  */
 367
 368       lmo.r_map_offset = 4;
 369       lmo.r_map_size   = 4;
 370
 371       lmo.link_map_size = 20;   /* Actual size is 552, but this is all we
 372                                    need.  */
 373
 374       lmo.l_addr_offset = 0;
 375       lmo.l_addr_size   = 4;
 376
 377       lmo.l_name_offset = 4;
 378       lmo.l_name_size   = 4;
 379
 380       lmo.l_next_offset = 12;
 381       lmo.l_next_size   = 4;
 382
 383       lmo.l_prev_offset = 16;
 384       lmo.l_prev_size   = 4;
 385     }
 386
 387     return lmp;
 388 }
 389
 390 CORE_ADDR
 391 arm_linux_skip_solib_resolver (CORE_ADDR pc)
 392 {
 393   return glibc_skip_solib_resolver (pc);
 394 }
 395
 396 /* The constants below were determined by examining the following files
 397    in the linux kernel sources:
 398
 399       arch/arm/kernel/signal.c
 400           - see SWI_SYS_SIGRETURN and SWI_SYS_RT_SIGRETURN
 401       include/asm-arm/unistd.h
 402           - see __NR_sigreturn, __NR_rt_sigreturn, and __NR_SYSCALL_BASE */
 403
 404 #define ARM_LINUX_SIGRETURN_INSTR       0xef900077
 405 #define ARM_LINUX_RT_SIGRETURN_INSTR    0xef9000ad
 406
 407 /* arm_linux_in_sigtramp determines if PC points at one of the
 408    instructions which cause control to return to the Linux kernel upon
 409    return from a signal handler.  FUNC_NAME is unused.  */
 410
 411 int
 412 arm_linux_in_sigtramp (CORE_ADDR pc, char *func_name)
 413 {
 414   unsigned long inst;
 415
 416   inst = read_memory_integer (pc, 4);
 417
 418   return (inst == ARM_LINUX_SIGRETURN_INSTR
 419           || inst == ARM_LINUX_RT_SIGRETURN_INSTR);
 420
 421 }
 422
 423 /* arm_linux_sigcontext_register_address returns the address in the
 424    sigcontext of register REGNO given a stack pointer value SP and
 425    program counter value PC.  The value 0 is returned if PC is not
 426    pointing at one of the signal return instructions or if REGNO is
 427    not saved in the sigcontext struct.  */
 428
 429 CORE_ADDR
 430 arm_linux_sigcontext_register_address (CORE_ADDR sp, CORE_ADDR pc, int regno)
 431 {
 432   unsigned long inst;
 433   CORE_ADDR reg_addr = 0;
 434
 435   inst = read_memory_integer (pc, 4);
 436
 437   if (inst == ARM_LINUX_SIGRETURN_INSTR
 438       || inst == ARM_LINUX_RT_SIGRETURN_INSTR)
 439     {
 440       CORE_ADDR sigcontext_addr;
 441
 442       /* The sigcontext structure is at different places for the two
 443          signal return instructions.  For ARM_LINUX_SIGRETURN_INSTR,
 444          it starts at the SP value.  For ARM_LINUX_RT_SIGRETURN_INSTR,
 445          it is at SP+8.  For the latter instruction, it may also be
 446          the case that the address of this structure may be determined
 447          by reading the 4 bytes at SP, but I'm not convinced this is
 448          reliable.
 449
 450          In any event, these magic constants (0 and 8) may be
 451          determined by examining struct sigframe and struct
 452          rt_sigframe in arch/arm/kernel/signal.c in the Linux kernel
 453          sources.  */
 454
 455       if (inst == ARM_LINUX_RT_SIGRETURN_INSTR)
 456         sigcontext_addr = sp + 8;
 457       else /* inst == ARM_LINUX_SIGRETURN_INSTR */
 458         sigcontext_addr = sp + 0;
 459
 460       /* The layout of the sigcontext structure for ARM GNU/Linux is
 461          in include/asm-arm/sigcontext.h in the Linux kernel sources.
 462
 463          There are three 4-byte fields which precede the saved r0
 464          field.  (This accounts for the 12 in the code below.)  The
 465          sixteen registers (4 bytes per field) follow in order.  The
 466          PSR value follows the sixteen registers which accounts for
 467          the constant 19 below. */
 468
 469       if (0 <= regno && regno <= ARM_PC_REGNUM)
 470         reg_addr = sigcontext_addr + 12 + (4 * regno);
 471       else if (regno == ARM_PS_REGNUM)
 472         reg_addr = sigcontext_addr + 19 * 4;
 473     }
 474
 475   return reg_addr;
 476 }
 477
 478 static void
 479 arm_linux_init_abi (struct gdbarch_info info,
 480                     struct gdbarch *gdbarch)
 481 {
 482   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 483
 484   tdep->lowest_pc = 0x8000;
 485   if (info.byte_order == BFD_ENDIAN_BIG)
 486     tdep->arm_breakpoint = arm_linux_arm_be_breakpoint;
 487   else
 488     tdep->arm_breakpoint = arm_linux_arm_le_breakpoint;
 489   tdep->arm_breakpoint_size = sizeof (arm_linux_arm_le_breakpoint);
 490
 491   tdep->fp_model = ARM_FLOAT_FPA;
 492
 493   tdep->jb_pc = ARM_LINUX_JB_PC;
 494   tdep->jb_elt_size = ARM_LINUX_JB_ELEMENT_SIZE;
 495
 496   set_solib_svr4_fetch_link_map_offsets
 497     (gdbarch, arm_linux_svr4_fetch_link_map_offsets);
 498
 499   set_gdbarch_deprecated_call_dummy_words (gdbarch, arm_linux_call_dummy_words);
 500   set_gdbarch_deprecated_sizeof_call_dummy_words (gdbarch, sizeof (arm_linux_call_dummy_words));
 501
 502   /* The following two overrides shouldn't be needed.  */
 503   set_gdbarch_deprecated_extract_return_value (gdbarch, arm_linux_extract_return_value);
 504   set_gdbarch_deprecated_push_arguments (gdbarch, arm_linux_push_arguments);
 505
 506   /* Shared library handling.  */
 507   set_gdbarch_in_solib_call_trampoline (gdbarch, in_plt_section);
 508   set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);
 509 }
 510
 511 void
 512 _initialize_arm_linux_tdep (void)
 513 {
 514   gdbarch_register_osabi (bfd_arch_arm, 0, GDB_OSABI_LINUX,
 515                           arm_linux_init_abi);
 516 }