/* Object file "section" support for the BFD library. Copyright (C) 1990-1991 Free Software Foundation, Inc. Written by Cygnus Support. This file is part of BFD, the Binary File Descriptor library. 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. */ /*doc* @section Sections Sections are supported in BFD in @code{section.c}. The raw data contained within a BFD is maintained through the section abstraction. A single BFD may have any number of sections, and keeps hold of them by pointing to the first, each one points to the next in the list. @menu * Section Input:: * Section Output:: * typedef asection:: * section prototypes:: @end menu @node Section Input, Section Output,,Sections @comment node-name, next, previous, up @subsection Section Input When a BFD is opened for reading, the section structures are created and attatched to the BFD. Each section has a name which describes the section in the outside world - for example, @code{a.out} would contain at least three sections, called @code{.text}, @code{.data} and @code{.bss}. Sometimes a BFD will contain more than the 'natural' number of sections. A back end may attatch other sections containing constructor data, or an application may add a section (using bfd_make_section) to the sections attatched to an already open BFD. For example, the linker creates a supernumary section @code{COMMON} for each input file's BFD to hold information about common storage. The raw data is not necessarily read in at the same time as the section descriptor is created. Some targets may leave the data in place until a @code{bfd_get_section_contents} call is made. Other back ends may read in all the data at once - For example; an S-record file has to be read once to determine the size of the data. An IEEE-695 file doesn't contain raw data in sections, but data and relocation expressions intermixed, so the data area has to be parsed to get out the data and relocations. @node Section Output,typedef asection,Section Input,Sections @subsection Section Output To write a new object style BFD, the various sections to be written have to be created. They are attatched to the BFD in the same way as input sections, data is written to the sections using @code{bfd_set_section_contents}. The linker uses the fields @code{output_section} and @code{output_offset} to create an output file. The data to be written comes from input sections attatched to the output sections. The output section structure can be considered a filter for the input section, the output section determines the vma of the output data and the name, but the input section determines the offset into the output section of the data to be written. Eg to create a section "O", starting at 0x100, 0x123 long, containing two subsections, "A" at offset 0x0 (ie at vma 0x100) and "B" at offset 0x20 (ie at vma 0x120) the structures would look like: *+ section name "A" output_offset 0x00 size 0x20 output_section -----------> section name "O" | vma 0x100 section name "B" | size 0x123 output_offset 0x20 | size 0x103 | output_section --------| *- */ #include "sysdep.h" #include "bfd.h" #include "libbfd.h" /*doc* @node typedef asection,section prototypes,Section Output,Sections @subsection typedef asection */ /*proto* The shape of a section struct: *+++ $typedef struct sec { The name of the section, the name isn't a copy, the pointer is the same as that passed to bfd_make_section. $ CONST char *name; The next section in the list belonging to the BFD, or NULL. $ struct sec *next; The field flags contains attributes of the section. Some of these flags are read in from the object file, and some are synthesized from other information. $flagword flags; $#define SEC_NO_FLAGS 0x000 Tells the OS to allocate space for this section when loaded. This would clear for a section containing debug information only. $#define SEC_ALLOC 0x001 Tells the OS to load the section from the file when loading. This would be clear for a .bss section $#define SEC_LOAD 0x002 The section contains data still to be relocated, so there will be some relocation information too. $#define SEC_RELOC 0x004 Obsolete ? $#define SEC_BALIGN 0x008 A signal to the OS that the section contains read only data. $#define SEC_READONLY 0x010 The section contains code only. $#define SEC_CODE 0x020 The section contains data only. $#define SEC_DATA 0x040 The section will reside in ROM. $#define SEC_ROM 0x080 The section contains constructor information. This section type is used by the linker to create lists of constructors and destructors used by @code{g++}. When a back end sees a symbol which should be used in a constructor list, it creates a new section for the type of name (eg @code{__CTOR_LIST__}), attatches the symbol to it and builds a relocation. To build the lists of constructors, all the linker has to to is catenate all the sections called @code{__CTOR_LIST__} and relocte the data contained within - exactly the operations it would peform on standard data. $#define SEC_CONSTRUCTOR 0x100 The section is a constuctor, and should be placed at the end of the .. $#define SEC_CONSTRUCTOR_TEXT 0x1100 $#define SEC_CONSTRUCTOR_DATA 0x2100 $#define SEC_CONSTRUCTOR_BSS 0x3100 The section has contents - a bss section could be @code{SEC_ALLOC} | @code{SEC_HAS_CONTENTS}, a debug section could be @code{SEC_HAS_CONTENTS} $#define SEC_HAS_CONTENTS 0x200 An instruction to the linker not to output sections containing this flag even if they have information which would normally be written. $#define SEC_NEVER_LOAD 0x400 The base address of the section in the address space of the target. $ bfd_vma vma; The size of the section in bytes of the loaded section. This contains a value even if the section has no contents (eg, the size of @code{.bss}). $ bfd_size_type size; If this section is going to be output, then this value is the offset into the output section of the first byte in the input section. Eg, if this was going to start at the 100th byte in the output section, this value would be 100. $ bfd_vma output_offset; The output section through which to map on output. $ struct sec *output_section; The alignment requirement of the section, as an exponent - eg 3 aligns to 2^3 (or 8) $ unsigned int alignment_power; If an input section, a pointer to a vector of relocation records for the data in this section. $ struct reloc_cache_entry *relocation; If an output section, a pointer to a vector of pointers to relocation records for the data in this section. $ struct reloc_cache_entry **orelocation; The number of relocation records in one of the above $ unsigned reloc_count; Which section is it 0..nth $ int index; Information below is back end specific - and not always used or updated File position of section data $ file_ptr filepos; File position of relocation info $ file_ptr rel_filepos; File position of line data $ file_ptr line_filepos; Pointer to data for applications $ PTR userdata; $ struct lang_output_section *otheruserdata; Attached line number information $ alent *lineno; Number of line number records $ unsigned int lineno_count; When a section is being output, this value changes as more linenumbers are written out $ file_ptr moving_line_filepos; what the section number is in the target world $ unsigned int target_index; $ PTR used_by_bfd; If this is a constructor section then here is a list of the relocations created to relocate items within it. $ struct relent_chain *constructor_chain; The BFD which owns the section. $ bfd *owner; $} asection ; *--- */ /*doc* @node section prototypes,Section,typedef section,Sections @subsection section prototypes */ /*proto* bfd_get_section_by_name Runs through the provided @var{abfd} and returns the @code{asection} who's name matches that provided, otherwise NULL. @xref{Sections}, for more information. *; PROTO(asection *, bfd_get_section_by_name, (bfd *abfd, CONST char *name)); */ asection * DEFUN(bfd_get_section_by_name,(abfd, name), bfd *abfd AND CONST char *name) { asection *sect; for (sect = abfd->sections; sect != NULL; sect = sect->next) if (!strcmp (sect->name, name)) return sect; return NULL; } /*proto* bfd_make_section This function creates a new empty section called @var{name} and attatches it to the end of the chain of sections for the BFD supplied. An attempt to create a section with a name which is already in use, returns the old section by that name instead. Possible errors are: @table @code @item invalid_operation If output has already started for this BFD. @item no_memory If obstack alloc fails. @end table *; PROTO(asection *, bfd_make_section, (bfd *, CONST char *name)); */ sec_ptr DEFUN(bfd_make_section,(abfd, name), bfd *abfd AND CONST char * name) { asection *newsect; asection ** prev = &abfd->sections; asection * sect = abfd->sections; if (abfd->output_has_begun) { bfd_error = invalid_operation; return NULL; } while (sect) { if (!strcmp(sect->name, name)) return sect; prev = §->next; sect = sect->next; } newsect = (asection *) bfd_zalloc(abfd, sizeof (asection)); if (newsect == NULL) { bfd_error = no_memory; return NULL; } newsect->name = name; newsect->index = abfd->section_count++; newsect->flags = SEC_NO_FLAGS; newsect->userdata = 0; newsect->next = (asection *)NULL; newsect->relocation = (arelent *)NULL; newsect->reloc_count = 0; newsect->line_filepos =0; newsect->owner = abfd; if (BFD_SEND (abfd, _new_section_hook, (abfd, newsect)) != true) { free (newsect); return NULL; } *prev = newsect; return newsect; } /*proto* bfd_set_section_flags Attempts to set the attributes of the section named in the BFD supplied to the value. Returns true on success, false on error. Possible error returns are: @table @code @item invalid operation The section cannot have one or more of the attributes requested. For example, a .bss section in @code{a.out} may not have the @code{SEC_HAS_CONTENTS} field set. @end table *; PROTO(boolean, bfd_set_section_flags, (bfd *, asection *, flagword)); */ boolean DEFUN(bfd_set_section_flags,(abfd, section, flags), bfd *abfd AND sec_ptr section AND flagword flags) { if ((flags & bfd_applicable_section_flags (abfd)) != flags) { bfd_error = invalid_operation; return false; } section->flags = flags; return true; } /*proto* bfd_map_over_sections Calls the provided function @var{func} for each section attatched to the BFD @var{abfd}, passing @var{obj} as an argument. The function will be called as if by @example func(abfd, the_section, obj); @end example *; PROTO(void, bfd_map_over_sections, (bfd *abfd, void (*func)(), PTR obj)); This is the prefered method for iterating over sections, an alternative would be to use a loop: @example section *p; for (p = abfd->sections; p != NULL; p = p->next) func(abfd, p, ...) @end example */ /*VARARGS2*/ void DEFUN(bfd_map_over_sections,(abfd, operation, user_storage), bfd *abfd AND void (*operation)() AND PTR user_storage) { asection *sect; int i = 0; for (sect = abfd->sections; sect != NULL; i++, sect = sect->next) (*operation) (abfd, sect, user_storage); if (i != abfd->section_count) /* Debugging */ abort(); } /*proto* bfd_set_section_size Sets @var{section} to the size @var{val}. If the operation is ok, then @code{true} is returned, else @code{false}. Possible error returns: @table @code @item invalid_operation Writing has started to the BFD, so setting the size is invalid @end table *; PROTO(boolean, bfd_set_section_size, (bfd *, asection *, bfd_size_type val)); */ boolean DEFUN(bfd_set_section_size,(abfd, ptr, val), bfd *abfd AND sec_ptr ptr AND bfd_size_type val) { /* Once you've started writing to any section you cannot create or change the size of any others. */ if (abfd->output_has_begun) { bfd_error = invalid_operation; return false; } ptr->size = val; return true; } /*proto* bfd_set_section_contents Sets the contents of the section @var{section} in BFD @var{abfd} to the data starting in memory at @var{data}. The data is written to the output section starting at offset @var{offset} for @var{count} bytes. Normally @code{true} is returned, else @code{false}. Possible error returns are: @table @code @item no_contents The output section does not have the @code{SEC_HAS_CONTENTS} attribute, so nothing can be written to it. @item and some more too @end table This routine is front end to the back end function @code{_bfd_set_section_contents}. *; PROTO(boolean, bfd_set_section_contents, (bfd *abfd, asection *section, PTR data, file_ptr offset, bfd_size_type count)); */ boolean DEFUN(bfd_set_section_contents,(abfd, section, location, offset, count), bfd *abfd AND sec_ptr section AND PTR location AND file_ptr offset AND bfd_size_type count) { if (!(bfd_get_section_flags(abfd, section) & SEC_HAS_CONTENTS)) { bfd_error = no_contents; return(false); } if (BFD_SEND (abfd, _bfd_set_section_contents, (abfd, section, location, offset, count))) { abfd->output_has_begun = true; return true; } return false; } /*proto* bfd_get_section_contents This function reads data from @var{section} in BFD @var{abfd} into memory starting at @var{location}. The data is read at an offset of @var{offset} from the start of the input section, and is read for @var{count} bytes. If the contents of a constuctor with the @code{SEC_CONSTUCTOR} flag set are requested, then the @var{location} is filled with zeroes. If no errors occur, @code{true} is returned, else @code{false}. Possible errors are: @table @code @item unknown yet @end table *; PROTO(boolean, bfd_get_section_contents, (bfd *abfd, asection *section, PTR location, file_ptr offset, bfd_size_type count)); */ boolean DEFUN(bfd_get_section_contents,(abfd, section, location, offset, count), bfd *abfd AND sec_ptr section AND PTR location AND file_ptr offset AND bfd_size_type count) { if (section->flags & SEC_CONSTRUCTOR) { memset(location, 0, (unsigned)count); return true; } else { return (BFD_SEND (abfd, _bfd_get_section_contents, (abfd, section, location, offset, count))); } }