elfread.c

早期freebsd实现

		  case 'b':
			if (!strcmp ("Bbss.bss", sym->name))
			  index = SECT_OFF_BSS;
			break;
		  case 'd':
			if (!strcmp ("Ddata.data", sym->name))
			  index = SECT_OFF_DATA;
			break;
		  case 'r':
			if (!strcmp ("Drodata.rodata", sym->name))
			  index = SECT_OFF_RODATA;
			break;
		}
	      if (index > 0)
		{
		  /* We have some new info.  Allocate a sectinfo, if
		     needed, and fill it in.  */
		  if (!sectinfo)
		    {
		      sectinfo = (struct stab_section_info *)
				 xmmalloc (objfile -> md,
					   sizeof (*sectinfo));
		      memset ((PTR) sectinfo, 0, sizeof (*sectinfo));
		      if (!filesym)
			complain (&section_info_complaint, (char *)sym->name);
		      else
			sectinfo->filename = (char *)filesym->name;
		    }
		  if (sectinfo->sections[index])
		    complain (&section_info_dup_complaint,
			      (char *)sectinfo->filename);

		  symaddr = sym -> value;
		  /* Relocate all non-absolute symbols by base address.  */
		  if (sym -> section != &bfd_abs_section)
		      symaddr += addr;
		  sectinfo->sections[index] = symaddr;
		}
	    }
	}
      do_cleanups (back_to);
    }
}

/* Scan and build partial symbols for a symbol file.
   We have been initialized by a call to elf_symfile_init, which 
   currently does nothing.

   SECTION_OFFSETS is a set of offsets to apply to relocate the symbols
   in each section.  We simplify it down to a single offset for all
   symbols.  FIXME.

   MAINLINE is true if we are reading the main symbol
   table (as opposed to a shared lib or dynamically loaded file).

   This function only does the minimum work necessary for letting the
   user "name" things symbolically; it does not read the entire symtab.
   Instead, it reads the external and static symbols and puts them in partial
   symbol tables.  When more extensive information is requested of a
   file, the corresponding partial symbol table is mutated into a full
   fledged symbol table by going back and reading the symbols
   for real.

   We look for sections with specific names, to tell us what debug
   format to look for:  FIXME!!!

   dwarf_build_psymtabs() builds psymtabs for DWARF symbols;
   elfstab_build_psymtabs() handles STABS symbols.

   Note that ELF files have a "minimal" symbol table, which looks a lot
   like a COFF symbol table, but has only the minimal information necessary
   for linking.  We process this also, and use the information to
   build gdb's minimal symbol table.  This gives us some minimal debugging
   capability even for files compiled without -g.  */

static void
elf_symfile_read (objfile, section_offsets, mainline)
     struct objfile *objfile;
     struct section_offsets *section_offsets;
     int mainline;
{
  bfd *abfd = objfile->obfd;
  struct elfinfo ei;
  struct dbx_symfile_info *dbx;
  struct cleanup *back_to;
  asection *text_sect;
  CORE_ADDR offset;

  init_minimal_symbol_collection ();
  back_to = make_cleanup (discard_minimal_symbols, 0);

  memset ((char *) &ei, 0, sizeof (ei));

  /* Allocate struct to keep track of the symfile */
  objfile->sym_private = (PTR)
    xmmalloc (objfile -> md, sizeof (struct dbx_symfile_info));
  memset ((char *) objfile->sym_private, 0, sizeof (struct dbx_symfile_info));
  make_cleanup (free_elfinfo, (PTR) objfile);

  /* Process the normal ELF symbol table first.  This may write some 
     chain of info into the dbx_symfile_info in objfile->sym_private,
     which can later be used by elfstab_offset_sections.  */

  /* FIXME, should take a section_offsets param, not just an offset.  */
  offset = ANOFFSET (section_offsets, 0);
  elf_symtab_read (abfd, offset, objfile);

  /* Now process debugging information, which is contained in
     special ELF sections.  We first have to find them... */

  bfd_map_over_sections (abfd, elf_locate_sections, (PTR) &ei);
  if (ei.dboffset && ei.lnoffset)
    {
      /* DWARF sections */
      dwarf_build_psymtabs (objfile,
			    section_offsets, mainline,
			    ei.dboffset, ei.dbsize,
			    ei.lnoffset, ei.lnsize);
    }
  if (ei.stabsect)
    {
      /* STABS sections */

      /* FIXME:  Sun didn't really know how to implement this well.
	 They made .stab sections that don't point to the .stabstr
	 section with the sh_link field.  BFD doesn't make string table
	 sections visible to the caller.  So we have to search the
	 ELF section table, not the BFD section table, for the string
	 table.  */
      struct elf_internal_shdr *elf_sect;

      elf_sect = bfd_elf_find_section (abfd, ".stabstr");
      if (elf_sect)
	elfstab_build_psymtabs (objfile,
  	  section_offsets,
	  mainline,
	  ei.stabsect->filepos,				/* .stab offset */
	  bfd_get_section_size_before_reloc (ei.stabsect),/* .stab size */
	  (file_ptr) elf_sect->sh_offset,		/* .stabstr offset */
	  elf_sect->sh_size);				/* .stabstr size */
    }

  if (!have_partial_symbols ())
    {
      wrap_here ("");
      printf_filtered ("(no debugging symbols found)...");
      wrap_here ("");
    }

  /* Install any minimal symbols that have been collected as the current
     minimal symbols for this objfile. */

  install_minimal_symbols (objfile);

  do_cleanups (back_to);
}

/* This cleans up the objfile's sym_private pointer, and the chain of
   stab_section_info's, that might be dangling from it.  */

static void
free_elfinfo (objp)
     PTR objp;
{
  struct objfile *objfile = (struct objfile *)objp;
  struct dbx_symfile_info *dbxinfo = (struct dbx_symfile_info *)
				     objfile->sym_private;
  struct stab_section_info *ssi, *nssi;

  ssi = dbxinfo->stab_section_info;
  while (ssi)
    {
      nssi = ssi->next;
      mfree (objfile->md, ssi);
      ssi = nssi;
    }

  dbxinfo->stab_section_info = 0;	/* Just say No mo info about this.  */
}


/* Initialize anything that needs initializing when a completely new symbol
   file is specified (not just adding some symbols from another file, e.g. a
   shared library).

   We reinitialize buildsym, since we may be reading stabs from an ELF file.  */

static void
elf_new_init (ignore)
     struct objfile *ignore;
{
  stabsread_new_init ();
  buildsym_new_init ();
}

/* Perform any local cleanups required when we are done with a particular
   objfile.  I.E, we are in the process of discarding all symbol information
   for an objfile, freeing up all memory held for it, and unlinking the
   objfile struct from the global list of known objfiles. */

static void
elf_symfile_finish (objfile)
     struct objfile *objfile;
{
  if (objfile -> sym_private != NULL)
    {
      mfree (objfile -> md, objfile -> sym_private);
    }
}

/* ELF specific initialization routine for reading symbols.

   It is passed a pointer to a struct sym_fns which contains, among other
   things, the BFD for the file whose symbols are being read, and a slot for
   a pointer to "private data" which we can fill with goodies.

   For now at least, we have nothing in particular to do, so this function is
   just a stub. */

static void
elf_symfile_init (ignore)
     struct objfile *ignore;
{
}

/* ELF specific parsing routine for section offsets.

   Plain and simple for now.  */

static
struct section_offsets *
elf_symfile_offsets (objfile, addr)
     struct objfile *objfile;
     CORE_ADDR addr;
{
  struct section_offsets *section_offsets;
  int i;
 
  section_offsets = (struct section_offsets *)
    obstack_alloc (&objfile -> psymbol_obstack,
		   sizeof (struct section_offsets) +
		          sizeof (section_offsets->offsets) * (SECT_OFF_MAX-1));

  for (i = 0; i < SECT_OFF_MAX; i++)
    ANOFFSET (section_offsets, i) = addr;
  
  return section_offsets;
}

/* When handling an ELF file that contains Sun STABS debug info,
   some of the debug info is relative to the particular chunk of the
   section that was generated in its individual .o file.  E.g.
   offsets to static variables are relative to the start of the data
   segment *for that module before linking*.  This information is
   painfully squirreled away in the ELF symbol table as local symbols
   with wierd names.  Go get 'em when needed.  */

void
elfstab_offset_sections (objfile, pst)
     struct objfile *objfile;
     struct partial_symtab *pst;
{
  char *filename = pst->filename;
  struct dbx_symfile_info *dbx = (struct dbx_symfile_info *)
				 objfile->sym_private;
  struct stab_section_info *maybe = dbx->stab_section_info;
  struct stab_section_info *questionable = 0;
  int i;
  char *p;

  /* The ELF symbol info doesn't include path names, so strip the path
     (if any) from the psymtab filename.  */
  while (0 != (p = strchr (filename, '/')))
    filename = p+1;

  /* FIXME:  This linear search could speed up significantly
     if it was chained in the right order to match how we search it,
     and if we unchained when we found a match. */
  for (; maybe; maybe = maybe->next)
    {
      if (filename[0] == maybe->filename[0]
	  && !strcmp (filename, maybe->filename))
	{
	  /* We found a match.  But there might be several source files
	     (from different directories) with the same name.  */
	  if (0 == maybe->found)
	    break;
	  questionable = maybe;		/* Might use it later.  */
	}
    }

  if (maybe == 0 && questionable != 0)
    {
      complain (&stab_info_questionable_complaint, filename);
      maybe = questionable;
    }

  if (maybe)
    {
      /* Found it!  Allocate a new psymtab struct, and fill it in.  */
      maybe->found++;
      pst->section_offsets = (struct section_offsets *)
	obstack_alloc (&objfile -> psymbol_obstack,
		       sizeof (struct section_offsets) +
	       sizeof (pst->section_offsets->offsets) * (SECT_OFF_MAX-1));

      for (i = 0; i < SECT_OFF_MAX; i++)
	ANOFFSET (pst->section_offsets, i) = maybe->sections[i];
      return;
    }

  /* We were unable to find any offsets for this file.  Complain.  */
  if (dbx->stab_section_info)		/* If there *is* any info, */
    complain (&stab_info_mismatch_complaint, filename);
}

/*  Register that we are able to handle ELF object file formats and DWARF
    debugging formats.

    Unlike other object file formats, where the debugging information format
    is implied by the object file format, the ELF object file format and the
    DWARF debugging information format are two distinct, and potentially
    separate entities.  I.E. it is perfectly possible to have ELF objects
    with debugging formats other than DWARF.  And it is conceivable that the
    DWARF debugging format might be used with another object file format,
    like COFF, by simply using COFF's custom section feature.

    GDB, and to a lesser extent BFD, should support the notion of separate
    object file formats and debugging information formats.  For now, we just
    use "elf" in the same sense as "a.out" or "coff", to imply both the ELF
    object file format and the DWARF debugging format. */

static struct sym_fns elf_sym_fns =
{
  "elf",		/* sym_name: name or name prefix of BFD target type */
  3,			/* sym_namelen: number of significant sym_name chars */
  elf_new_init,		/* sym_new_init: init anything gbl to entire symtab */
  elf_symfile_init,	/* sym_init: read initial info, setup for sym_read() */
  elf_symfile_read,	/* sym_read: read a symbol file into symtab */
  elf_symfile_finish,	/* sym_finish: finished with file, cleanup */
  elf_symfile_offsets,	/* sym_offsets:  Translate ext. to int. relocation */
  NULL			/* next: pointer to next struct sym_fns */
};

void
_initialize_elfread ()
{
  add_symtab_fns (&elf_sym_fns);
}