* objfiles.h (struct objfile): Clean up comments for

[thirdparty/binutils-gdb.git] / gdb / objfiles.h

/* Definitions for symbol file management in GDB.
   Copyright (C) 1992 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */

#if !defined (OBJFILES_H)
#define OBJFILES_H

/* This structure maintains information on a per-objfile basis about the
   "entry point" of the objfile, and the scope within which the entry point
   exists.  It is possible that gdb will see more than one objfile that is
   executable, each with it's own entry point.

   For example, for dynamically linked executables in SVR4, the dynamic linker
   code is contained within the shared C library, which is actually executable
   and is run by the kernel first when an exec is done of a user executable
   that is dynamically linked.  The dynamic linker within the shared C library
   then maps in the various program segments in the user executable and jumps
   to the user executable's recorded entry point, as if the call had been made
   directly by the kernel.

   The traditional gdb method of using this info is to use the recorded entry
   point to set the variables entry_file_lowpc and entry_file_highpc from
   the debugging information, where these values are the starting address
   (inclusive) and ending address (exclusive) of the instruction space in the
   executable which correspond to the "startup file", I.E. crt0.o in most
   cases.  This file is assumed to be a startup file and frames with pc's
   inside it are treated as nonexistent.  Setting these variables is necessary
   so that backtraces do not fly off the bottom of the stack (or top, depending
   upon your stack orientation).

   Gdb also supports an alternate method to avoid running off the top/bottom
   of the stack.

   There are two frames that are "special", the frame for the function
   containing the process entry point, since it has no predecessor frame,
   and the frame for the function containing the user code entry point
   (the main() function), since all the predecessor frames are for the
   process startup code.  Since we have no guarantee that the linked
   in startup modules have any debugging information that gdb can use,
   we need to avoid following frame pointers back into frames that might
   have been built in the startup code, as we might get hopelessly 
   confused.  However, we almost always have debugging information
   available for main().

   These variables are used to save the range of PC values which are valid
   within the main() function and within the function containing the process
   entry point.  If we always consider the frame for main() as the outermost
   frame when debugging user code, and the frame for the process entry
   point function as the outermost frame when debugging startup code, then
   all we have to do is have FRAME_CHAIN_VALID return false whenever a
   frame's current PC is within the range specified by these variables.
   In essence, we set "ceilings" in the frame chain beyond which we will
   not proceed when following the frame chain back up the stack.

   A nice side effect is that we can still debug startup code without
   running off the end of the frame chain, assuming that we have usable
   debugging information in the startup modules, and if we choose to not
   use the block at main, or can't find it for some reason, everything
   still works as before.  And if we have no startup code debugging
   information but we do have usable information for main(), backtraces
   from user code don't go wandering off into the startup code.

   To use this method, define your FRAME_CHAIN_VALID macro like:

        #define FRAME_CHAIN_VALID(chain, thisframe)     \
          (chain != 0                                   \
           && !(inside_main_func ((thisframe)->pc))     \
           && !(inside_entry_func ((thisframe)->pc)))

   and add initializations of the four scope controlling variables inside
   the object file / debugging information processing modules.  */

struct entry_info
{
  
  /* The value we should use for this objects entry point.
     The illegal/unknown value needs to be something other than 0, ~0
     for instance, which is much less likely than 0. */

  CORE_ADDR entry_point;

  /* Start (inclusive) and end (exclusive) of function containing the
     entry point. */

  CORE_ADDR entry_func_lowpc;
  CORE_ADDR entry_func_highpc;

  /* Start (inclusive) and end (exclusive) of object file containing the
     entry point. */
  
  CORE_ADDR entry_file_lowpc;
  CORE_ADDR entry_file_highpc;

  /* Start (inclusive) and end (exclusive) of the user code main() function. */

  CORE_ADDR main_func_lowpc;
  CORE_ADDR main_func_highpc;

};


/* Sections in an objfile.

   It is strange that we have both this notion of "sections"
   and the one used by section_offsets.  Section as used
   here, (currently at least) means a BFD section, and the sections
   are set up from the BFD sections in allocate_objfile.

   The sections in section_offsets have their meaning determined by
   the symbol format, and they are set up by the sym_offsets function
   for that symbol file format.

   I'm not sure this could or should be changed, however.  */

struct obj_section {
  CORE_ADDR     addr;    /* lowest address in section */
  CORE_ADDR     endaddr; /* 1+highest address in section */

  /* This field is being used for nefarious purposes by syms_from_objfile.
     It is said to be redundant with section_offsets; it's not really being
     used that way, however, it's some sort of hack I don't understand
     and am not going to try to eliminate (yet, anyway).  FIXME.

     It was documented as "offset between (end)addr and actual memory
     addresses", but that's not true; addr & endaddr are actual memory
     addresses.  */
  CORE_ADDR offset;
     
  sec_ptr       sec_ptr; /* BFD section pointer */

  /* Objfile this section is part of.  Not currently used, but I'm sure
     that someone will want the bfd that the sec_ptr goes with or something
     like that before long.  */
  struct objfile *objfile;
};

/* Master structure for keeping track of each input file from which
   gdb reads symbols.  One of these is allocated for each such file we
   access, e.g. the exec_file, symbol_file, and any shared library object
   files. */

struct objfile
{

  /* All struct objfile's are chained together by their next pointers.
     The global variable "object_files" points to the first link in this
     chain.

     FIXME:  There is a problem here if the objfile is reusable, and if
     multiple users are to be supported.  The problem is that the objfile
     list is linked through a member of the objfile struct itself, which
     is only valid for one gdb process.  The list implementation needs to
     be changed to something like:

     struct list {struct list *next; struct objfile *objfile};

     where the list structure is completely maintained separately within
     each gdb process. */

  struct objfile *next;

  /* The object file's name.  Malloc'd; free it if you free this struct.  */

  char *name;

  /* Some flag bits for this objfile. */

  unsigned short flags;

  /* Each objfile points to a linked list of symtabs derived from this file,
     one symtab structure for each compilation unit (source file).  Each link
     in the symtab list contains a backpointer to this objfile. */

  struct symtab *symtabs;

  /* Each objfile points to a linked list of partial symtabs derived from
     this file, one partial symtab structure for each compilation unit
     (source file). */

  struct partial_symtab *psymtabs;

  /* List of freed partial symtabs, available for re-use */

  struct partial_symtab *free_psymtabs;

  /* The object file's BFD.  Can be null, in which case bfd_open (name) and
     put the result here.  */

  bfd *obfd;

  /* The modification timestamp of the object file, as of the last time
     we read its symbols.  */

  long mtime;

  /* Obstacks to hold objects that should be freed when we load a new symbol
     table from this object file. */

  struct obstack psymbol_obstack;       /* Partial symbols */
  struct obstack symbol_obstack;        /* Full symbols */
  struct obstack type_obstack;          /* Types */

  /* Vectors of all partial symbols read in from file.  The actual data
     is stored in the psymbol_obstack. */

  struct psymbol_allocation_list global_psymbols;
  struct psymbol_allocation_list static_psymbols;

  /* Each file contains a pointer to an array of minimal symbols for all
     global symbols that are defined within the file.  The array is terminated
     by a "null symbol", one that has a NULL pointer for the name and a zero
     value for the address.  This makes it easy to walk through the array
     when passed a pointer to somewhere in the middle of it.  There is also
     a count of the number of symbols, which does include the terminating
     null symbol.  The array itself, as well as all the data that it points
     to, should be allocated on the symbol_obstack for this file. */

  struct minimal_symbol *msymbols;
  int minimal_symbol_count;

  /* For object file formats which don't specify fundamental types, gdb
     can create such types.  For now, it maintains a vector of pointers
     to these internally created fundamental types on a per objfile basis,
     however it really should ultimately keep them on a per-compilation-unit
     basis, to account for linkage-units that consist of a number of
     compilation units that may have different fundamental types, such as
     linking C modules with ADA modules, or linking C modules that are
     compiled with 32-bit ints with C modules that are compiled with 64-bit
     ints (not inherently evil with a smarter linker). */

  struct type **fundamental_types;

  /* The mmalloc() malloc-descriptor for this objfile if we are using
     the memory mapped malloc() package to manage storage for this objfile's
     data.  NULL if we are not. */

  PTR md;

  /* The file descriptor that was used to obtain the mmalloc descriptor
     for this objfile.  If we call mmalloc_detach with the malloc descriptor
     we should then close this file descriptor. */

  int mmfd;

  /* Structure which keeps track of functions that manipulate objfile's
     of the same type as this objfile.  I.E. the function to read partial
     symbols for example.  Note that this structure is in statically
     allocated memory, and is shared by all objfiles that use the
     object module reader of this type. */

  struct sym_fns *sf;

  /* The per-objfile information about the entry point, the scope (file/func)
     containing the entry point, and the scope of the user's main() func. */

  struct entry_info ei;

  /* Hook for information for use by the symbol reader (currently used
     for information shared by sym_init and sym_read).  It is
     typically a pointer to malloc'd memory.  The symbol reader's finish
     function is responsible for freeing the memory thusly allocated.  */

  PTR sym_private;

  /* Hook for target-architecture-specific information.  This must
     point to memory allocated on one of the obstacks in this objfile,
     so that it gets freed automatically when reading a new object
     file. */

  PTR obj_private;

  /* Set of relocation offsets to apply to each section.
     Currently on the psymbol_obstack (which makes no sense, but I'm
     not sure it's harming anything).

     These offsets indicate that all symbols (including partial and
     minimal symbols) which have been read have been relocated by this
     much.  Symbols which are yet to be read need to be relocated by
     it.  */

  struct section_offsets *section_offsets;
  int num_sections;

  /* set of section begin and end addresses used to map pc addresses
     into sections.  Currently on the psymbol_obstack (which makes no
     sense, but I'm not sure it's harming anything).  */

  struct obj_section
    *sections,
    *sections_end;
};

/* Defines for the objfile flag word. */

/* Gdb can arrange to allocate storage for all objects related to a
   particular objfile in a designated section of it's address space,
   managed at a low level by mmap() and using a special version of
   malloc that handles malloc/free/realloc on top of the mmap() interface.
   This allows the "internal gdb state" for a particular objfile to be
   dumped to a gdb state file and subsequently reloaded at a later time. */

#define OBJF_MAPPED     (1 << 0)        /* Objfile data is mmap'd */

/* When using mapped/remapped predigested gdb symbol information, we need
   a flag that indicates that we have previously done an initial symbol
   table read from this particular objfile.  We can't just look for the
   absence of any of the three symbol tables (msymbols, psymtab, symtab)
   because if the file has no symbols for example, none of these will
   exist. */

#define OBJF_SYMS       (1 << 1)        /* Have tried to read symbols */

/* The object file that the main symbol table was loaded from (e.g. the
   argument to the "symbol-file" or "file" command).  */

extern struct objfile *symfile_objfile;

/* When we need to allocate a new type, we need to know which type_obstack
   to allocate the type on, since there is one for each objfile.  The places
   where types are allocated are deeply buried in function call hierarchies
   which know nothing about objfiles, so rather than trying to pass a
   particular objfile down to them, we just do an end run around them and
   set current_objfile to be whatever objfile we expect to be using at the
   time types are being allocated.  For instance, when we start reading
   symbols for a particular objfile, we set current_objfile to point to that
   objfile, and when we are done, we set it back to NULL, to ensure that we
   never put a type someplace other than where we are expecting to put it.
   FIXME:  Maybe we should review the entire type handling system and
   see if there is a better way to avoid this problem. */

extern struct objfile *current_objfile;

/* All known objfiles are kept in a linked list.  This points to the
   root of this list. */

extern struct objfile *object_files;

/* Declarations for functions defined in objfiles.c */

extern struct objfile *
allocate_objfile PARAMS ((bfd *, int));

extern void
unlink_objfile PARAMS ((struct objfile *));

extern void
free_objfile PARAMS ((struct objfile *));

extern void
free_all_objfiles PARAMS ((void));

extern void
objfile_relocate PARAMS ((struct objfile *, struct section_offsets *));

extern int
have_partial_symbols PARAMS ((void));

extern int
have_full_symbols PARAMS ((void));

/* Functions for dealing with the minimal symbol table, really a misc
   address<->symbol mapping for things we don't have debug symbols for.  */

extern int
have_minimal_symbols PARAMS ((void));

extern struct obj_section *
find_pc_section PARAMS((CORE_ADDR pc));

/* Traverse all object files.  ALL_OBJFILES_SAFE works even if you delete
   the objfile during the traversal.  */

#define ALL_OBJFILES(obj) \
  for ((obj) = object_files; (obj) != NULL; (obj) = (obj)->next)

#define ALL_OBJFILES_SAFE(obj,nxt) \
  for ((obj) = object_files;       \
       (obj) != NULL? ((nxt)=(obj)->next,1) :0; \
       (obj) = (nxt))


/* Traverse all symtabs in one objfile.  */

#define ALL_OBJFILE_SYMTABS(objfile, s) \
    for ((s) = (objfile) -> symtabs; (s) != NULL; (s) = (s) -> next)

/* Traverse all psymtabs in one objfile.  */

#define ALL_OBJFILE_PSYMTABS(objfile, p) \
    for ((p) = (objfile) -> psymtabs; (p) != NULL; (p) = (p) -> next)

/* Traverse all minimal symbols in one objfile.  */

#define ALL_OBJFILE_MSYMBOLS(objfile, m) \
    for ((m) = (objfile) -> msymbols; SYMBOL_NAME(m) != NULL; (m)++)


/* Traverse all symtabs in all objfiles.  */

#define ALL_SYMTABS(objfile, s) \
  ALL_OBJFILES (objfile)         \
    ALL_OBJFILE_SYMTABS (objfile, s)

/* Traverse all psymtabs in all objfiles.  */

#define ALL_PSYMTABS(objfile, p) \
  ALL_OBJFILES (objfile)         \
    ALL_OBJFILE_PSYMTABS (objfile, p)

/* Traverse all minimal symbols in all objfiles.  */

#define ALL_MSYMBOLS(objfile, m) \
  ALL_OBJFILES (objfile)         \
    if ((objfile)->msymbols)     \
      ALL_OBJFILE_MSYMBOLS (objfile, m)

#endif  /* !defined (OBJFILES_H) */