gdb/mipsread.c

   1 /* Read a symbol table in MIPS' format (Third-Eye).
   2
   3    Copyright (C) 1986-2020 Free Software Foundation, Inc.
   4
   5    Contributed by Alessandro Forin (af@cs.cmu.edu) at CMU.  Major work
   6    by Per Bothner, John Gilmore and Ian Lance Taylor at Cygnus Support.
   7
   8    This file is part of GDB.
   9
  10    This program is free software; you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation; either version 3 of the License, or
  13    (at your option) any later version.
  14
  15    This program is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  22
  23 /* Read symbols from an ECOFF file.  Most of the work is done in
  24    mdebugread.c.  */
  25
  26 #include "defs.h"
  27 #include "bfd.h"
  28 #include "symtab.h"
  29 #include "objfiles.h"
  30 #include "stabsread.h"
  31 #include "mdebugread.h"
  32
  33 #include "coff/sym.h"
  34 #include "coff/internal.h"
  35 #include "coff/ecoff.h"
  36 #include "libcoff.h"            /* Private BFD COFF information.  */
  37 #include "libecoff.h"           /* Private BFD ECOFF information.  */
  38 #include "elf/common.h"
  39 #include "elf/internal.h"
  40 #include "elf/mips.h"
  41
  42 #include "psymtab.h"
  43
  44 static void
  45 read_alphacoff_dynamic_symtab (minimal_symbol_reader &,
  46                                struct objfile *objfile);
  47
  48 /* Initialize anything that needs initializing when a completely new
  49    symbol file is specified (not just adding some symbols from another
  50    file, e.g. a shared library).  */
  51
  52 static void
  53 mipscoff_new_init (struct objfile *ignore)
  54 {
  55   stabsread_new_init ();
  56 }
  57
  58 /* Initialize to read a symbol file (nothing to do).  */
  59
  60 static void
  61 mipscoff_symfile_init (struct objfile *objfile)
  62 {
  63 }
  64
  65 /* Read a symbol file from a file.  */
  66
  67 static void
  68 mipscoff_symfile_read (struct objfile *objfile, symfile_add_flags symfile_flags)
  69 {
  70   bfd *abfd = objfile->obfd;
  71
  72   minimal_symbol_reader reader (objfile);
  73
  74   /* Now that the executable file is positioned at symbol table,
  75      process it and define symbols accordingly.  */
  76
  77   if (!((*ecoff_backend (abfd)->debug_swap.read_debug_info)
  78         (abfd, NULL, &ecoff_data (abfd)->debug_info)))
  79     error (_("Error reading symbol table: %s"), bfd_errmsg (bfd_get_error ()));
  80
  81   mdebug_build_psymtabs (reader, objfile, &ecoff_backend (abfd)->debug_swap,
  82                          &ecoff_data (abfd)->debug_info);
  83
  84   /* Add alpha coff dynamic symbols.  */
  85
  86   read_alphacoff_dynamic_symtab (reader, objfile);
  87
  88   /* Install any minimal symbols that have been collected as the current
  89      minimal symbols for this objfile.  */
  90
  91   reader.install ();
  92 }
  93
  94 /* Perform any local cleanups required when we are done with a
  95    particular objfile.  */
  96
  97 static void
  98 mipscoff_symfile_finish (struct objfile *objfile)
  99 {
 100 }
 101
 102 /* Alpha OSF/1 encapsulates the dynamic symbols in ELF format in a
 103    standard COFF section.  The ELF format for the symbols differs from
 104    the format defined in elf/external.h.  It seems that a normal ELF
 105    32-bit format is used, and the representation only changes because
 106    longs are 64-bit on the alpha.  In addition, the handling of
 107    text/data section indices for symbols is different from the ELF
 108    ABI.  As the BFD linker currently does not support dynamic linking
 109    on the alpha, there seems to be no reason to pollute BFD with
 110    another mixture of object file formats for now.  */
 111
 112 /* Format of an alpha external ELF symbol.  */
 113
 114 typedef struct
 115 {
 116   unsigned char st_name[4];     /* Symbol name, index in string table.  */
 117   unsigned char st_pad[4];      /* Pad to long word boundary.  */
 118   unsigned char st_value[8];    /* Value of the symbol.  */
 119   unsigned char st_size[4];     /* Associated symbol size.  */
 120   unsigned char st_info[1];     /* Type and binding attributes.  */
 121   unsigned char st_other[1];    /* No defined meaning, 0.  */
 122   unsigned char st_shndx[2];    /* Associated section index.  */
 123 } Elfalpha_External_Sym;
 124
 125 /* Format of an alpha external ELF dynamic info structure.  */
 126
 127 typedef struct
 128 {
 129   unsigned char d_tag[4];       /* Tag.  */
 130   unsigned char d_pad[4];       /* Pad to long word boundary.  */
 131   union
 132   {
 133     unsigned char d_ptr[8];     /* Pointer value.  */
 134     unsigned char d_val[4];     /* Integer value.  */
 135   }
 136   d_un;
 137 } Elfalpha_External_Dyn;
 138
 139 /* Struct to obtain the section pointers for alpha dynamic symbol info.  */
 140
 141 struct alphacoff_dynsecinfo
 142 {
 143   asection *sym_sect;           /* Section pointer for .dynsym section.  */
 144   asection *str_sect;           /* Section pointer for .dynstr section.  */
 145   asection *dyninfo_sect;       /* Section pointer for .dynamic section.  */
 146   asection *got_sect;           /* Section pointer for .got section.  */
 147 };
 148
 149 /* We are called once per section from read_alphacoff_dynamic_symtab.
 150    We need to examine each section we are passed, check to see if it
 151    is something we are interested in processing, and if so, stash away
 152    some access information for the section.  */
 153
 154 static void
 155 alphacoff_locate_sections (bfd *ignore_abfd, asection *sectp, void *sip)
 156 {
 157   struct alphacoff_dynsecinfo *si;
 158
 159   si = (struct alphacoff_dynsecinfo *) sip;
 160
 161   if (strcmp (sectp->name, ".dynsym") == 0)
 162     si->sym_sect = sectp;
 163   else if (strcmp (sectp->name, ".dynstr") == 0)
 164     si->str_sect = sectp;
 165   else if (strcmp (sectp->name, ".dynamic") == 0)
 166     si->dyninfo_sect = sectp;
 167   else if (strcmp (sectp->name, ".got") == 0)
 168       si->got_sect = sectp;
 169 }
 170
 171 /* Scan an alpha dynamic symbol table for symbols of interest and add
 172    them to the minimal symbol table.  */
 173
 174 static void
 175 read_alphacoff_dynamic_symtab (minimal_symbol_reader &reader,
 176                                struct objfile *objfile)
 177 {
 178   bfd *abfd = objfile->obfd;
 179   struct alphacoff_dynsecinfo si;
 180   int sym_count;
 181   int i;
 182   int stripped;
 183   Elfalpha_External_Sym *x_symp;
 184   gdb_byte *dyninfo_p;
 185   gdb_byte *dyninfo_end;
 186   int got_entry_size = 8;
 187   int dt_mips_local_gotno = -1;
 188   int dt_mips_gotsym = -1;
 189
 190   /* We currently only know how to handle alpha dynamic symbols.  */
 191   if (bfd_get_arch (abfd) != bfd_arch_alpha)
 192     return;
 193
 194   /* Locate the dynamic symbols sections and read them in.  */
 195   memset ((char *) &si, 0, sizeof (si));
 196   bfd_map_over_sections (abfd, alphacoff_locate_sections, (void *) & si);
 197   if (si.sym_sect == NULL || si.str_sect == NULL
 198       || si.dyninfo_sect == NULL || si.got_sect == NULL)
 199     return;
 200
 201   gdb::byte_vector sym_sec (bfd_section_size (si.sym_sect));
 202   gdb::byte_vector str_sec (bfd_section_size (si.str_sect));
 203   gdb::byte_vector dyninfo_sec (bfd_section_size (si.dyninfo_sect));
 204   gdb::byte_vector got_sec (bfd_section_size (si.got_sect));
 205
 206   if (!bfd_get_section_contents (abfd, si.sym_sect, sym_sec.data (),
 207                                  (file_ptr) 0, sym_sec.size ()))
 208     return;
 209   if (!bfd_get_section_contents (abfd, si.str_sect, str_sec.data (),
 210                                  (file_ptr) 0, str_sec.size ()))
 211     return;
 212   if (!bfd_get_section_contents (abfd, si.dyninfo_sect, dyninfo_sec.data (),
 213                                  (file_ptr) 0, dyninfo_sec.size ()))
 214     return;
 215   if (!bfd_get_section_contents (abfd, si.got_sect, got_sec.data (),
 216                                  (file_ptr) 0, got_sec.size ()))
 217     return;
 218
 219   /* Find the number of local GOT entries and the index for the
 220      first dynamic symbol in the GOT.  */
 221   for ((dyninfo_p = dyninfo_sec.data (),
 222         dyninfo_end = dyninfo_p + dyninfo_sec.size ());
 223        dyninfo_p < dyninfo_end;
 224        dyninfo_p += sizeof (Elfalpha_External_Dyn))
 225     {
 226       Elfalpha_External_Dyn *x_dynp = (Elfalpha_External_Dyn *) dyninfo_p;
 227       long dyn_tag;
 228
 229       dyn_tag = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp->d_tag);
 230       if (dyn_tag == DT_NULL)
 231         break;
 232       else if (dyn_tag == DT_MIPS_LOCAL_GOTNO)
 233         {
 234           if (dt_mips_local_gotno < 0)
 235             dt_mips_local_gotno
 236               = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp->d_un.d_val);
 237         }
 238       else if (dyn_tag == DT_MIPS_GOTSYM)
 239         {
 240           if (dt_mips_gotsym < 0)
 241             dt_mips_gotsym
 242               = bfd_h_get_32 (abfd, (bfd_byte *) x_dynp->d_un.d_val);
 243         }
 244     }
 245   if (dt_mips_local_gotno < 0 || dt_mips_gotsym < 0)
 246     return;
 247
 248   /* Scan all dynamic symbols and enter them into the minimal symbol
 249      table if appropriate.  */
 250   sym_count = sym_sec.size () / sizeof (Elfalpha_External_Sym);
 251   stripped = (bfd_get_symcount (abfd) == 0);
 252
 253   /* Skip first symbol, which is a null dummy.  */
 254   for (i = 1, x_symp = (Elfalpha_External_Sym *) sym_sec.data () + 1;
 255        i < sym_count;
 256        i++, x_symp++)
 257     {
 258       unsigned long strx;
 259       char *name;
 260       bfd_vma sym_value;
 261       unsigned char sym_info;
 262       unsigned int sym_shndx;
 263       int isglobal;
 264       enum minimal_symbol_type ms_type;
 265
 266       strx = bfd_h_get_32 (abfd, (bfd_byte *) x_symp->st_name);
 267       if (strx >= str_sec.size ())
 268         continue;
 269       name = (char *) (str_sec.data () + strx);
 270       if (*name == '\0' || *name == '.')
 271         continue;
 272
 273       sym_value = bfd_h_get_64 (abfd, (bfd_byte *) x_symp->st_value);
 274       sym_info = bfd_h_get_8 (abfd, (bfd_byte *) x_symp->st_info);
 275       sym_shndx = bfd_h_get_16 (abfd, (bfd_byte *) x_symp->st_shndx);
 276       if (sym_shndx >= (SHN_LORESERVE & 0xffff))
 277         sym_shndx += SHN_LORESERVE - (SHN_LORESERVE & 0xffff);
 278       isglobal = (ELF_ST_BIND (sym_info) == STB_GLOBAL);
 279
 280       if (sym_shndx == SHN_UNDEF)
 281         {
 282           /* Handle undefined functions which are defined in a shared
 283              library.  */
 284           if (ELF_ST_TYPE (sym_info) != STT_FUNC
 285               || ELF_ST_BIND (sym_info) != STB_GLOBAL)
 286             continue;
 287
 288           ms_type = mst_solib_trampoline;
 289
 290           /* If sym_value is nonzero, it points to the shared library
 291              trampoline entry, which is what we are looking for.
 292
 293              If sym_value is zero, then we have to get the GOT entry
 294              for the symbol.
 295
 296              If the GOT entry is nonzero, it represents the quickstart
 297              address of the function and we use that as the symbol
 298              value.
 299
 300              If the GOT entry is zero, the function address has to be
 301              resolved by the runtime loader before the executable is
 302              started.  We are unable to find any meaningful address
 303              for these functions in the executable file, so we skip
 304              them.  */
 305           if (sym_value == 0)
 306             {
 307               int got_entry_offset =
 308                 (i - dt_mips_gotsym + dt_mips_local_gotno) * got_entry_size;
 309
 310               if (got_entry_offset < 0
 311                   || got_entry_offset >= got_sec.size ())
 312                 continue;
 313               sym_value =
 314                 bfd_h_get_64 (abfd,
 315                               (bfd_byte *) (got_sec.data ()
 316                                             + got_entry_offset));
 317               if (sym_value == 0)
 318                 continue;
 319             }
 320         }
 321       else
 322         {
 323           /* Symbols defined in the executable itself.  We only care
 324              about them if this is a stripped executable, otherwise
 325              they have been retrieved from the normal symbol table
 326              already.  */
 327           if (!stripped)
 328             continue;
 329
 330           if (sym_shndx == SHN_MIPS_TEXT)
 331             {
 332               if (isglobal)
 333                 ms_type = mst_text;
 334               else
 335                 ms_type = mst_file_text;
 336             }
 337           else if (sym_shndx == SHN_MIPS_DATA)
 338             {
 339               if (isglobal)
 340                 ms_type = mst_data;
 341               else
 342                 ms_type = mst_file_data;
 343             }
 344           else if (sym_shndx == SHN_MIPS_ACOMMON)
 345             {
 346               if (isglobal)
 347                 ms_type = mst_bss;
 348               else
 349                 ms_type = mst_file_bss;
 350             }
 351           else if (sym_shndx == SHN_ABS)
 352             {
 353               ms_type = mst_abs;
 354             }
 355           else
 356             {
 357               continue;
 358             }
 359         }
 360
 361       reader.record (name, sym_value, ms_type);
 362     }
 363 }
 364
 365 /* Initialization.  */
 366
 367 static const struct sym_fns ecoff_sym_fns =
 368 {
 369   mipscoff_new_init,            /* init anything gbl to entire symtab */
 370   mipscoff_symfile_init,        /* read initial info, setup for sym_read() */
 371   mipscoff_symfile_read,        /* read a symbol file into symtab */
 372   NULL,                         /* sym_read_psymbols */
 373   mipscoff_symfile_finish,      /* finished with file, cleanup */
 374   default_symfile_offsets,      /* dummy FIXME til implem sym reloc */
 375   default_symfile_segments,     /* Get segment information from a file.  */
 376   NULL,
 377   default_symfile_relocate,     /* Relocate a debug section.  */
 378   NULL,                         /* sym_probe_fns */
 379   &psym_functions
 380 };
 381
 382 void
 383 _initialize_mipsread (void)
 384 {
 385   add_symtab_fns (bfd_target_ecoff_flavour, &ecoff_sym_fns);
 386 }