gdb/i386-tdep.c

   1 /* Intel 386 target-dependent stuff.
   2    Copyright (C) 1988, 1989, 1991, 1994 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20 #include "defs.h"
  21 #include "frame.h"
  22 #include "inferior.h"
  23 #include "gdbcore.h"
  24 #include "target.h"
  25 <<<<<<< i386-tdep.c
  26 #include "floatformat.h"
  27 ||||||| 1.26
  28 =======
  29 #include "symtab.h"
  30 >>>>>>> 1.27
  31
  32 static long
  33 i386_get_frame_setup PARAMS ((int));
  34
  35 static void
  36 i386_follow_jump PARAMS ((void));
  37
  38 static void
  39 codestream_read PARAMS ((unsigned char *, int));
  40
  41 static void
  42 codestream_seek PARAMS ((int));
  43
  44 static unsigned char
  45 codestream_fill PARAMS ((int));
  46
  47 /* helper functions for tm-i386.h */
  48
  49 /* Stdio style buffering was used to minimize calls to ptrace, but this
  50    buffering did not take into account that the code section being accessed
  51    may not be an even number of buffers long (even if the buffer is only
  52    sizeof(int) long).  In cases where the code section size happened to
  53    be a non-integral number of buffers long, attempting to read the last
  54    buffer would fail.  Simply using target_read_memory and ignoring errors,
  55    rather than read_memory, is not the correct solution, since legitimate
  56    access errors would then be totally ignored.  To properly handle this
  57    situation and continue to use buffering would require that this code
  58    be able to determine the minimum code section size granularity (not the
  59    alignment of the section itself, since the actual failing case that
  60    pointed out this problem had a section alignment of 4 but was not a
  61    multiple of 4 bytes long), on a target by target basis, and then
  62    adjust it's buffer size accordingly.  This is messy, but potentially
  63    feasible.  It probably needs the bfd library's help and support.  For
  64    now, the buffer size is set to 1.  (FIXME -fnf) */
  65
  66 #define CODESTREAM_BUFSIZ 1     /* Was sizeof(int), see note above. */
  67 static CORE_ADDR codestream_next_addr;
  68 static CORE_ADDR codestream_addr;
  69 static unsigned char codestream_buf[CODESTREAM_BUFSIZ];
  70 static int codestream_off;
  71 static int codestream_cnt;
  72
  73 #define codestream_tell() (codestream_addr + codestream_off)
  74 #define codestream_peek() (codestream_cnt == 0 ? \
  75                            codestream_fill(1): codestream_buf[codestream_off])
  76 #define codestream_get() (codestream_cnt-- == 0 ? \
  77                          codestream_fill(0) : codestream_buf[codestream_off++])
  78
  79 static unsigned char
  80 codestream_fill (peek_flag)
  81     int peek_flag;
  82 {
  83   codestream_addr = codestream_next_addr;
  84   codestream_next_addr += CODESTREAM_BUFSIZ;
  85   codestream_off = 0;
  86   codestream_cnt = CODESTREAM_BUFSIZ;
  87   read_memory (codestream_addr, (char *) codestream_buf, CODESTREAM_BUFSIZ);
  88
  89   if (peek_flag)
  90     return (codestream_peek());
  91   else
  92     return (codestream_get());
  93 }
  94
  95 static void
  96 codestream_seek (place)
  97     int place;
  98 {
  99   codestream_next_addr = place / CODESTREAM_BUFSIZ;
 100   codestream_next_addr *= CODESTREAM_BUFSIZ;
 101   codestream_cnt = 0;
 102   codestream_fill (1);
 103   while (codestream_tell() != place)
 104     codestream_get ();
 105 }
 106
 107 static void
 108 codestream_read (buf, count)
 109      unsigned char *buf;
 110      int count;
 111 {
 112   unsigned char *p;
 113   int i;
 114   p = buf;
 115   for (i = 0; i < count; i++)
 116     *p++ = codestream_get ();
 117 }
 118
 119 /* next instruction is a jump, move to target */
 120
 121 static void
 122 i386_follow_jump ()
 123 {
 124   unsigned char buf[4];
 125   long delta;
 126
 127   int data16;
 128   CORE_ADDR pos;
 129
 130   pos = codestream_tell ();
 131
 132   data16 = 0;
 133   if (codestream_peek () == 0x66)
 134     {
 135       codestream_get ();
 136       data16 = 1;
 137     }
 138
 139   switch (codestream_get ())
 140     {
 141     case 0xe9:
 142       /* relative jump: if data16 == 0, disp32, else disp16 */
 143       if (data16)
 144         {
 145           codestream_read (buf, 2);
 146           delta = extract_signed_integer (buf, 2);
 147
 148           /* include size of jmp inst (including the 0x66 prefix).  */
 149           pos += delta + 4;
 150         }
 151       else
 152         {
 153           codestream_read (buf, 4);
 154           delta = extract_signed_integer (buf, 4);
 155
 156           pos += delta + 5;
 157         }
 158       break;
 159     case 0xeb:
 160       /* relative jump, disp8 (ignore data16) */
 161       codestream_read (buf, 1);
 162       /* Sign-extend it.  */
 163       delta = extract_signed_integer (buf, 1);
 164
 165       pos += delta + 2;
 166       break;
 167     }
 168   codestream_seek (pos);
 169 }
 170
 171 /*
 172  * find & return amound a local space allocated, and advance codestream to
 173  * first register push (if any)
 174  *
 175  * if entry sequence doesn't make sense, return -1, and leave
 176  * codestream pointer random
 177  */
 178
 179 static long
 180 i386_get_frame_setup (pc)
 181      int pc;
 182 {
 183   unsigned char op;
 184
 185   codestream_seek (pc);
 186
 187   i386_follow_jump ();
 188
 189   op = codestream_get ();
 190
 191   if (op == 0x58)               /* popl %eax */
 192     {
 193       /*
 194        * this function must start with
 195        *
 196        *    popl %eax             0x58
 197        *    xchgl %eax, (%esp)  0x87 0x04 0x24
 198        * or xchgl %eax, 0(%esp) 0x87 0x44 0x24 0x00
 199        *
 200        * (the system 5 compiler puts out the second xchg
 201        * inst, and the assembler doesn't try to optimize it,
 202        * so the 'sib' form gets generated)
 203        *
 204        * this sequence is used to get the address of the return
 205        * buffer for a function that returns a structure
 206        */
 207       int pos;
 208       unsigned char buf[4];
 209       static unsigned char proto1[3] = { 0x87,0x04,0x24 };
 210       static unsigned char proto2[4] = { 0x87,0x44,0x24,0x00 };
 211       pos = codestream_tell ();
 212       codestream_read (buf, 4);
 213       if (memcmp (buf, proto1, 3) == 0)
 214         pos += 3;
 215       else if (memcmp (buf, proto2, 4) == 0)
 216         pos += 4;
 217
 218       codestream_seek (pos);
 219       op = codestream_get (); /* update next opcode */
 220     }
 221
 222   if (op == 0x55)               /* pushl %ebp */
 223     {
 224       /* check for movl %esp, %ebp - can be written two ways */
 225       switch (codestream_get ())
 226         {
 227         case 0x8b:
 228           if (codestream_get () != 0xec)
 229             return (-1);
 230           break;
 231         case 0x89:
 232           if (codestream_get () != 0xe5)
 233             return (-1);
 234           break;
 235         default:
 236           return (-1);
 237         }
 238       /* check for stack adjustment
 239        *
 240        *  subl $XXX, %esp
 241        *
 242        * note: you can't subtract a 16 bit immediate
 243        * from a 32 bit reg, so we don't have to worry
 244        * about a data16 prefix
 245        */
 246       op = codestream_peek ();
 247       if (op == 0x83)
 248         {
 249           /* subl with 8 bit immed */
 250           codestream_get ();
 251           if (codestream_get () != 0xec)
 252             /* Some instruction starting with 0x83 other than subl.  */
 253             {
 254               codestream_seek (codestream_tell () - 2);
 255               return 0;
 256             }
 257           /* subl with signed byte immediate
 258            * (though it wouldn't make sense to be negative)
 259            */
 260           return (codestream_get());
 261         }
 262       else if (op == 0x81)
 263         {
 264           char buf[4];
 265           /* Maybe it is subl with 32 bit immedediate.  */
 266           codestream_get();
 267           if (codestream_get () != 0xec)
 268             /* Some instruction starting with 0x81 other than subl.  */
 269             {
 270               codestream_seek (codestream_tell () - 2);
 271               return 0;
 272             }
 273           /* It is subl with 32 bit immediate.  */
 274           codestream_read ((unsigned char *)buf, 4);
 275           return extract_signed_integer (buf, 4);
 276         }
 277       else
 278         {
 279           return (0);
 280         }
 281     }
 282   else if (op == 0xc8)
 283     {
 284       char buf[2];
 285       /* enter instruction: arg is 16 bit unsigned immed */
 286       codestream_read ((unsigned char *)buf, 2);
 287       codestream_get (); /* flush final byte of enter instruction */
 288       return extract_unsigned_integer (buf, 2);
 289     }
 290   return (-1);
 291 }
 292
 293 /* Return number of args passed to a frame.
 294    Can return -1, meaning no way to tell.  */
 295
 296 int
 297 i386_frame_num_args (fi)
 298      struct frame_info *fi;
 299 {
 300 #if 1
 301   return -1;
 302 #else
 303   /* This loses because not only might the compiler not be popping the
 304      args right after the function call, it might be popping args from both
 305      this call and a previous one, and we would say there are more args
 306      than there really are.  */
 307
 308   int retpc;
 309   unsigned char op;
 310   struct frame_info *pfi;
 311
 312   /* on the 386, the instruction following the call could be:
 313      popl %ecx        -  one arg
 314      addl $imm, %esp  -  imm/4 args; imm may be 8 or 32 bits
 315      anything else    -  zero args  */
 316
 317   int frameless;
 318
 319   FRAMELESS_FUNCTION_INVOCATION (fi, frameless);
 320   if (frameless)
 321     /* In the absence of a frame pointer, GDB doesn't get correct values
 322        for nameless arguments.  Return -1, so it doesn't print any
 323        nameless arguments.  */
 324     return -1;
 325
 326   pfi = get_prev_frame_info (fi);
 327   if (pfi == 0)
 328     {
 329       /* Note:  this can happen if we are looking at the frame for
 330          main, because FRAME_CHAIN_VALID won't let us go into
 331          start.  If we have debugging symbols, that's not really
 332          a big deal; it just means it will only show as many arguments
 333          to main as are declared.  */
 334       return -1;
 335     }
 336   else
 337     {
 338       retpc = pfi->pc;
 339       op = read_memory_integer (retpc, 1);
 340       if (op == 0x59)
 341         /* pop %ecx */
 342         return 1;
 343       else if (op == 0x83)
 344         {
 345           op = read_memory_integer (retpc+1, 1);
 346           if (op == 0xc4)
 347             /* addl $<signed imm 8 bits>, %esp */
 348             return (read_memory_integer (retpc+2,1)&0xff)/4;
 349           else
 350             return 0;
 351         }
 352       else if (op == 0x81)
 353         { /* add with 32 bit immediate */
 354           op = read_memory_integer (retpc+1, 1);
 355           if (op == 0xc4)
 356             /* addl $<imm 32>, %esp */
 357             return read_memory_integer (retpc+2, 4) / 4;
 358           else
 359             return 0;
 360         }
 361       else
 362         {
 363           return 0;
 364         }
 365     }
 366 #endif
 367 }
 368
 369 /*
 370  * parse the first few instructions of the function to see
 371  * what registers were stored.
 372  *
 373  * We handle these cases:
 374  *
 375  * The startup sequence can be at the start of the function,
 376  * or the function can start with a branch to startup code at the end.
 377  *
 378  * %ebp can be set up with either the 'enter' instruction, or
 379  * 'pushl %ebp, movl %esp, %ebp' (enter is too slow to be useful,
 380  * but was once used in the sys5 compiler)
 381  *
 382  * Local space is allocated just below the saved %ebp by either the
 383  * 'enter' instruction, or by 'subl $<size>, %esp'.  'enter' has
 384  * a 16 bit unsigned argument for space to allocate, and the
 385  * 'addl' instruction could have either a signed byte, or
 386  * 32 bit immediate.
 387  *
 388  * Next, the registers used by this function are pushed.  In
 389  * the sys5 compiler they will always be in the order: %edi, %esi, %ebx
 390  * (and sometimes a harmless bug causes it to also save but not restore %eax);
 391  * however, the code below is willing to see the pushes in any order,
 392  * and will handle up to 8 of them.
 393  *
 394  * If the setup sequence is at the end of the function, then the
 395  * next instruction will be a branch back to the start.
 396  */
 397
 398 void
 399 i386_frame_find_saved_regs (fip, fsrp)
 400      struct frame_info *fip;
 401      struct frame_saved_regs *fsrp;
 402 {
 403   long locals;
 404   unsigned char op;
 405   CORE_ADDR dummy_bottom;
 406   CORE_ADDR adr;
 407   int i;
 408
 409   memset (fsrp, 0, sizeof *fsrp);
 410
 411   /* if frame is the end of a dummy, compute where the
 412    * beginning would be
 413    */
 414   dummy_bottom = fip->frame - 4 - REGISTER_BYTES - CALL_DUMMY_LENGTH;
 415
 416   /* check if the PC is in the stack, in a dummy frame */
 417   if (dummy_bottom <= fip->pc && fip->pc <= fip->frame)
 418     {
 419       /* all regs were saved by push_call_dummy () */
 420       adr = fip->frame;
 421       for (i = 0; i < NUM_REGS; i++)
 422         {
 423           adr -= REGISTER_RAW_SIZE (i);
 424           fsrp->regs[i] = adr;
 425         }
 426       return;
 427     }
 428
 429   locals = i386_get_frame_setup (get_pc_function_start (fip->pc));
 430
 431   if (locals >= 0)
 432     {
 433       adr = fip->frame - 4 - locals;
 434       for (i = 0; i < 8; i++)
 435         {
 436           op = codestream_get ();
 437           if (op < 0x50 || op > 0x57)
 438             break;
 439           fsrp->regs[op - 0x50] = adr;
 440           adr -= 4;
 441         }
 442     }
 443
 444   fsrp->regs[PC_REGNUM] = fip->frame + 4;
 445   fsrp->regs[FP_REGNUM] = fip->frame;
 446 }
 447
 448 /* return pc of first real instruction */
 449
 450 int
 451 i386_skip_prologue (pc)
 452      int pc;
 453 {
 454   unsigned char op;
 455   int i;
 456   static unsigned char pic_pat[6] = { 0xe8, 0, 0, 0, 0, /* call   0x0 */
 457                                       0x5b,             /* popl   %ebx */
 458                                     };
 459   CORE_ADDR pos;
 460
 461   if (i386_get_frame_setup (pc) < 0)
 462     return (pc);
 463
 464   /* found valid frame setup - codestream now points to
 465    * start of push instructions for saving registers
 466    */
 467
 468   /* skip over register saves */
 469   for (i = 0; i < 8; i++)
 470     {
 471       op = codestream_peek ();
 472       /* break if not pushl inst */
 473       if (op < 0x50 || op > 0x57)
 474         break;
 475       codestream_get ();
 476     }
 477
 478   /* The native cc on SVR4 in -K PIC mode inserts the following code to get
 479      the address of the global offset table (GOT) into register %ebx.
 480       call      0x0
 481       popl      %ebx
 482       movl      %ebx,x(%ebp)    (optional)
 483       addl      y,%ebx
 484      This code is with the rest of the prologue (at the end of the
 485      function), so we have to skip it to get to the first real
 486      instruction at the start of the function.  */
 487
 488   pos = codestream_tell ();
 489   for (i = 0; i < 6; i++)
 490     {
 491       op = codestream_get ();
 492       if (pic_pat [i] != op)
 493         break;
 494     }
 495   if (i == 6)
 496     {
 497       unsigned char buf[4];
 498       long delta = 6;
 499
 500       op = codestream_get ();
 501       if (op == 0x89)                   /* movl %ebx, x(%ebp) */
 502         {
 503           op = codestream_get ();
 504           if (op == 0x5d)               /* one byte offset from %ebp */
 505             {
 506               delta += 3;
 507               codestream_read (buf, 1);
 508             }
 509           else if (op == 0x9d)          /* four byte offset from %ebp */
 510             {
 511               delta += 6;
 512               codestream_read (buf, 4);
 513             }
 514           else                          /* unexpected instruction */
 515               delta = -1;
 516           op = codestream_get ();
 517         }
 518                                         /* addl y,%ebx */
 519       if (delta > 0 && op == 0x81 && codestream_get () == 0xc3)
 520         {
 521             pos += delta + 6;
 522         }
 523     }
 524   codestream_seek (pos);
 525
 526   i386_follow_jump ();
 527
 528   return (codestream_tell ());
 529 }
 530
 531 void
 532 i386_push_dummy_frame ()
 533 {
 534   CORE_ADDR sp = read_register (SP_REGNUM);
 535   int regnum;
 536   char regbuf[MAX_REGISTER_RAW_SIZE];
 537
 538   sp = push_word (sp, read_register (PC_REGNUM));
 539   sp = push_word (sp, read_register (FP_REGNUM));
 540   write_register (FP_REGNUM, sp);
 541   for (regnum = 0; regnum < NUM_REGS; regnum++)
 542     {
 543       read_register_gen (regnum, regbuf);
 544       sp = push_bytes (sp, regbuf, REGISTER_RAW_SIZE (regnum));
 545     }
 546   write_register (SP_REGNUM, sp);
 547 }
 548
 549 void
 550 i386_pop_frame ()
 551 {
 552   FRAME frame = get_current_frame ();
 553   CORE_ADDR fp;
 554   int regnum;
 555   struct frame_saved_regs fsr;
 556   struct frame_info *fi;
 557   char regbuf[MAX_REGISTER_RAW_SIZE];
 558
 559   fi = get_frame_info (frame);
 560   fp = fi->frame;
 561   get_frame_saved_regs (fi, &fsr);
 562   for (regnum = 0; regnum < NUM_REGS; regnum++)
 563     {
 564       CORE_ADDR adr;
 565       adr = fsr.regs[regnum];
 566       if (adr)
 567         {
 568           read_memory (adr, regbuf, REGISTER_RAW_SIZE (regnum));
 569           write_register_bytes (REGISTER_BYTE (regnum), regbuf,
 570                                 REGISTER_RAW_SIZE (regnum));
 571         }
 572     }
 573   write_register (FP_REGNUM, read_memory_integer (fp, 4));
 574   write_register (PC_REGNUM, read_memory_integer (fp + 4, 4));
 575   write_register (SP_REGNUM, fp + 8);
 576   flush_cached_frames ();
 577   set_current_frame ( create_new_frame (read_register (FP_REGNUM),
 578                                         read_pc ()));
 579 }
 580
 581 #ifdef GET_LONGJMP_TARGET
 582
 583 /* Figure out where the longjmp will land.  Slurp the args out of the stack.
 584    We expect the first arg to be a pointer to the jmp_buf structure from which
 585    we extract the pc (JB_PC) that we will land at.  The pc is copied into PC.
 586    This routine returns true on success. */
 587
 588 int
 589 get_longjmp_target(pc)
 590      CORE_ADDR *pc;
 591 {
 592   char buf[TARGET_PTR_BIT / TARGET_CHAR_BIT];
 593   CORE_ADDR sp, jb_addr;
 594
 595   sp = read_register (SP_REGNUM);
 596
 597   if (target_read_memory (sp + SP_ARG0, /* Offset of first arg on stack */
 598                           buf,
 599                           TARGET_PTR_BIT / TARGET_CHAR_BIT))
 600     return 0;
 601
 602   jb_addr = extract_address (buf, TARGET_PTR_BIT / TARGET_CHAR_BIT);
 603
 604   if (target_read_memory (jb_addr + JB_PC * JB_ELEMENT_SIZE, buf,
 605                           TARGET_PTR_BIT / TARGET_CHAR_BIT))
 606     return 0;
 607
 608   *pc = extract_address (buf, TARGET_PTR_BIT / TARGET_CHAR_BIT);
 609
 610   return 1;
 611 }
 612
 613 #endif /* GET_LONGJMP_TARGET */
 614
 615 #ifdef I386_AIX_TARGET
 616 /* On AIX, floating point values are returned in floating point registers.  */
 617
 618 void
 619 i386_extract_return_value(type, regbuf, valbuf)
 620      struct type *type;
 621      char regbuf[REGISTER_BYTES];
 622      char *valbuf;
 623 {
 624   if (TYPE_CODE_FLT == TYPE_CODE(type))
 625     {
 626       double d;
 627       /* 387 %st(0), gcc uses this */
 628       floatformat_to_double (&floatformat_i387_ext,
 629                              &regbuf[REGISTER_BYTE(FP0_REGNUM)],
 630                              &d);
 631       store_floating (valbuf, TYPE_LENGTH (type), d);
 632     }
 633   else
 634     {
 635       memcpy (valbuf, regbuf, TYPE_LENGTH (type));
 636     }
 637 }
 638 #endif /* I386_AIX_TARGET */
 639
 640 #ifdef I386V4_SIGTRAMP_SAVED_PC
 641 /* Get saved user PC for sigtramp from the pushed ucontext on the stack
 642    for all three variants of SVR4 sigtramps.  */
 643
 644 CORE_ADDR
 645 i386v4_sigtramp_saved_pc (frame)
 646      FRAME frame;
 647 {
 648   CORE_ADDR saved_pc_offset = 4;
 649   char *name = NULL;
 650
 651   find_pc_partial_function (frame->pc, &name,
 652                             (CORE_ADDR *)NULL,(CORE_ADDR *)NULL);
 653   if (name)
 654     {
 655       if (STREQ (name, "_sigreturn"))
 656         saved_pc_offset = 132 + 14 * 4;
 657       if (STREQ (name, "_sigacthandler"))
 658         saved_pc_offset = 80 + 14 * 4;
 659       if (STREQ (name, "sigvechandler"))
 660         saved_pc_offset = 120 + 14 * 4;
 661     }
 662
 663   if (frame->next)
 664     return read_memory_integer (frame->next->frame + saved_pc_offset, 4);
 665   return read_memory_integer (read_register (SP_REGNUM) + saved_pc_offset, 4);
 666 }
 667 #endif /* I386V4_SIGTRAMP_SAVED_PC */