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#### 2.6.4 typedef asection

Here is the section structure:

         typedef struct bfd_section
         {
           /* 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;

           /* A unique sequence number.  */
           int id;

           /* Which section in the bfd; 0..n-1 as sections are created in a bfd.  */
           int index;

           /* The next section in the list belonging to the BFD, or NULL.  */
           struct bfd_section *next;

           /* The previous section in the list belonging to the BFD, or NULL.  */
           struct bfd_section *prev;

           /* The field flags contains attributes of the section. Some
              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 loading.
              This is 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 is clear for a .bss section.  */
         #define SEC_LOAD       0x002

           /* The section contains data still to be relocated, so there is
              some relocation information too.  */
         #define SEC_RELOC      0x004

           /* A signal to the OS that the section contains read only data.  */
         #define SEC_READONLY   0x008

           /* The section contains code only.  */
         #define SEC_CODE       0x010

           /* The section contains data only.  */
         #define SEC_DATA       0x020

           /* The section will reside in ROM.  */
         #define SEC_ROM        0x040

           /* The section contains constructor information. This section
              type is used by the linker to create lists of constructors and
              destructors used by 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 (e.g., __CTOR_LIST__), attaches
              the symbol to it, and builds a relocation. To build the lists
              of constructors, all the linker has to do is catenate all the
              sections called __CTOR_LIST__ and relocate the data
              contained within - exactly the operations it would peform on
              standard data.  */
         #define SEC_CONSTRUCTOR 0x080

           /* The section has contents - a data section could be
              SEC_ALLOC | SEC_HAS_CONTENTS; a debug section could be
              SEC_HAS_CONTENTS  */
         #define SEC_HAS_CONTENTS 0x100

           /* An instruction to the linker to not output the section
              even if it has information which would normally be written.  */
         #define SEC_NEVER_LOAD 0x200

           /* The section contains thread local data.  */
         #define SEC_THREAD_LOCAL 0x400

           /* The section has GOT references.  This flag is only for the
              linker, and is currently only used by the elf32-hppa back end.
              It will be set if global offset table references were detected
              in this section, which indicate to the linker that the section
              contains PIC code, and must be handled specially when doing a
              static link.  */
         #define SEC_HAS_GOT_REF 0x800

           /* The section contains common symbols (symbols may be defined
              multiple times, the value of a symbol is the amount of
              space it requires, and the largest symbol value is the one
              used).  Most targets have exactly one of these (which we
              translate to bfd_com_section_ptr), but ECOFF has two.  */
         #define SEC_IS_COMMON 0x1000

           /* The section contains only debugging information.  For
              example, this is set for ELF .debug and .stab sections.
              strip tests this flag to see if a section can be
              discarded.  */
         #define SEC_DEBUGGING 0x2000

           /* The contents of this section are held in memory pointed to
              by the contents field.  This is checked by bfd_get_section_contents,
              and the data is retrieved from memory if appropriate.  */
         #define SEC_IN_MEMORY 0x4000

           /* The contents of this section are to be excluded by the
              linker for executable and shared objects unless those
              objects are to be further relocated.  */
         #define SEC_EXCLUDE 0x8000

           /* The contents of this section are to be sorted based on the sum of
              the symbol and addend values specified by the associated relocation
              entries.  Entries without associated relocation entries will be
              appended to the end of the section in an unspecified order.  */
         #define SEC_SORT_ENTRIES 0x10000

           /* When linking, duplicate sections of the same name should be
              discarded, rather than being combined into a single section as
              is usually done.  This is similar to how common symbols are
              handled.  See SEC_LINK_DUPLICATES below.  */
         #define SEC_LINK_ONCE 0x20000

           /* If SEC_LINK_ONCE is set, this bitfield describes how the linker
              should handle duplicate sections.  */
         #define SEC_LINK_DUPLICATES 0xc0000

           /* This value for SEC_LINK_DUPLICATES means that duplicate
              sections with the same name should simply be discarded.  */
         #define SEC_LINK_DUPLICATES_DISCARD 0x0

           /* This value for SEC_LINK_DUPLICATES means that the linker
              should warn if there are any duplicate sections, although
              it should still only link one copy.  */
         #define SEC_LINK_DUPLICATES_ONE_ONLY 0x40000

           /* This value for SEC_LINK_DUPLICATES means that the linker
              should warn if any duplicate sections are a different size.  */
         #define SEC_LINK_DUPLICATES_SAME_SIZE 0x80000

           /* This value for SEC_LINK_DUPLICATES means that the linker
              should warn if any duplicate sections contain different
              contents.  */
         #define SEC_LINK_DUPLICATES_SAME_CONTENTS \
           (SEC_LINK_DUPLICATES_ONE_ONLY | SEC_LINK_DUPLICATES_SAME_SIZE)

           /* This section was created by the linker as part of dynamic
              relocation or other arcane processing.  It is skipped when
              going through the first-pass output, trusting that someone
              else up the line will take care of it later.  */
         #define SEC_LINKER_CREATED 0x100000

           /* This section should not be subject to garbage collection.
              Also set to inform the linker that this section should not be
              listed in the link map as discarded.  */
         #define SEC_KEEP 0x200000

           /* This section contains "short" data, and should be placed
              "near" the GP.  */
         #define SEC_SMALL_DATA 0x400000

           /* Attempt to merge identical entities in the section.
              Entity size is given in the entsize field.  */
         #define SEC_MERGE 0x800000

           /* If given with SEC_MERGE, entities to merge are zero terminated
              strings where entsize specifies character size instead of fixed
              size entries.  */
         #define SEC_STRINGS 0x1000000

           /* This section contains data about section groups.  */
         #define SEC_GROUP 0x2000000

           /* The section is a COFF shared library section.  This flag is
              only for the linker.  If this type of section appears in
              the input file, the linker must copy it to the output file
              without changing the vma or size.  FIXME: Although this
              was originally intended to be general, it really is COFF
              specific (and the flag was renamed to indicate this).  It
              might be cleaner to have some more general mechanism to
              allow the back end to control what the linker does with
              sections.  */
         #define SEC_COFF_SHARED_LIBRARY 0x4000000

           /* This input section should be copied to output in reverse order
              as an array of pointers.  This is for ELF linker internal use
              only.  */
         #define SEC_ELF_REVERSE_COPY 0x4000000

           /* This section contains data which may be shared with other
              executables or shared objects. This is for COFF only.  */
         #define SEC_COFF_SHARED 0x8000000

           /* When a section with this flag is being linked, then if the size of
              the input section is less than a page, it should not cross a page
              boundary.  If the size of the input section is one page or more,
              it should be aligned on a page boundary.  This is for TI
              TMS320C54X only.  */
         #define SEC_TIC54X_BLOCK 0x10000000

           /* Conditionally link this section; do not link if there are no
              references found to any symbol in the section.  This is for TI
              TMS320C54X only.  */
         #define SEC_TIC54X_CLINK 0x20000000

           /* Indicate that section has the no read flag set. This happens
              when memory read flag isn't set. */
         #define SEC_COFF_NOREAD 0x40000000

           /*  End of section flags.  */

           /* Some internal packed boolean fields.  */

           /* See the vma field.  */
           unsigned int user_set_vma : 1;

           /* A mark flag used by some of the linker backends.  */
           unsigned int linker_mark : 1;

           /* Another mark flag used by some of the linker backends.  Set for
              output sections that have an input section.  */
           unsigned int linker_has_input : 1;

           /* Mark flag used by some linker backends for garbage collection.  */
           unsigned int gc_mark : 1;

           /* Section compression status.  */
           unsigned int compress_status : 2;
         #define COMPRESS_SECTION_NONE    0
         #define COMPRESS_SECTION_DONE    1
         #define DECOMPRESS_SECTION_SIZED 2

           /* The following flags are used by the ELF linker. */

           /* Mark sections which have been allocated to segments.  */
           unsigned int segment_mark : 1;

           /* Type of sec_info information.  */
           unsigned int sec_info_type:3;
         #define SEC_INFO_TYPE_NONE      0
         #define SEC_INFO_TYPE_STABS     1
         #define SEC_INFO_TYPE_MERGE     2
         #define SEC_INFO_TYPE_EH_FRAME  3
         #define SEC_INFO_TYPE_JUST_SYMS 4
         #define SEC_INFO_TYPE_TARGET    5

           /* Nonzero if this section uses RELA relocations, rather than REL.  */
           unsigned int use_rela_p:1;

           /* Bits used by various backends.  The generic code doesn't touch
              these fields.  */

           unsigned int sec_flg0:1;
           unsigned int sec_flg1:1;
           unsigned int sec_flg2:1;
           unsigned int sec_flg3:1;
           unsigned int sec_flg4:1;
           unsigned int sec_flg5:1;

           /* End of internal packed boolean fields.  */

           /*  The virtual memory address of the section - where it will be
               at run time.  The symbols are relocated against this.  The
               user_set_vma flag is maintained by bfd; if it's not set, the
               backend can assign addresses (for example, in a.out, where
               the default address for .data is dependent on the specific
               target and various flags).  */
           bfd_vma vma;

           /*  The load address of the section - where it would be in a
               rom image; really only used for writing section header
               information.  */
           bfd_vma lma;

           /* The size of the section in octets, as it will be output.
              Contains a value even if the section has no contents (e.g., the
              size of .bss).  */
           bfd_size_type size;

           /* For input sections, the original size on disk of the section, in
              octets.  This field should be set for any section whose size is
              changed by linker relaxation.  It is required for sections where
              the linker relaxation scheme doesn't cache altered section and
              reloc contents (stabs, eh_frame, SEC_MERGE, some coff relaxing
              targets), and thus the original size needs to be kept to read the
              section multiple times.  For output sections, rawsize holds the
              section size calculated on a previous linker relaxation pass.  */
           bfd_size_type rawsize;

           /* The compressed size of the section in octets.  */
           bfd_size_type compressed_size;

           /* Relaxation table. */
           struct relax_table *relax;

           /* Count of used relaxation table entries. */
           int relax_count;

           /* If this section is going to be output, then this value is the
              offset in *bytes* into the output section of the first byte in the
              input section (byte ==> smallest addressable unit on the
              target).  In most cases, if this was going to start at the
              100th octet (8-bit quantity) in the output section, this value
              would be 100.  However, if the target byte size is 16 bits
              (bfd_octets_per_byte is "2"), this value would be 50.  */
           bfd_vma output_offset;

           /* The output section through which to map on output.  */
           struct bfd_section *output_section;

           /* The alignment requirement of the section, as an exponent of 2 -
              e.g., 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;

           /* 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.  */
           void *userdata;

           /* If the SEC_IN_MEMORY flag is set, this points to the actual
              contents.  */
           unsigned char *contents;

           /* Attached line number information.  */
           alent *lineno;

           /* Number of line number records.  */
           unsigned int lineno_count;

           /* Entity size for merging purposes.  */
           unsigned int entsize;

           /* Points to the kept section if this section is a link-once section,
              and is discarded.  */
           struct bfd_section *kept_section;

           /* 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.  */
           int target_index;

           void *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;

           /* A symbol which points at this section only.  */
           struct bfd_symbol *symbol;
           struct bfd_symbol **symbol_ptr_ptr;

           /* Early in the link process, map_head and map_tail are used to build
              a list of input sections attached to an output section.  Later,
              output sections use these fields for a list of bfd_link_order
              structs.  */
           union {
             struct bfd_link_order *link_order;
             struct bfd_section *s;
           } map_head, map_tail;
         } asection;

         /* Relax table contains information about instructions which can
            be removed by relaxation -- replacing a long address with a
            short address.  */
         struct relax_table {
           /* Address where bytes may be deleted. */
           bfd_vma addr;

           /* Number of bytes to be deleted.  */
           int size;
         };

         /* These sections are global, and are managed by BFD.  The application
            and target back end are not permitted to change the values in
            these sections.  */
         extern asection _bfd_std_section[4];

         #define BFD_ABS_SECTION_NAME "*ABS*"
         #define BFD_UND_SECTION_NAME "*UND*"
         #define BFD_COM_SECTION_NAME "*COM*"
         #define BFD_IND_SECTION_NAME "*IND*"

         /* Pointer to the common section.  */
         #define bfd_com_section_ptr (&_bfd_std_section[0])
         /* Pointer to the undefined section.  */
         #define bfd_und_section_ptr (&_bfd_std_section[1])
         /* Pointer to the absolute section.  */
         #define bfd_abs_section_ptr (&_bfd_std_section[2])
         /* Pointer to the indirect section.  */
         #define bfd_ind_section_ptr (&_bfd_std_section[3])

         #define bfd_is_und_section(sec) ((sec) == bfd_und_section_ptr)
         #define bfd_is_abs_section(sec) ((sec) == bfd_abs_section_ptr)
         #define bfd_is_ind_section(sec) ((sec) == bfd_ind_section_ptr)

         #define bfd_is_const_section(SEC)              \
          (   ((SEC) == bfd_abs_section_ptr)            \
           || ((SEC) == bfd_und_section_ptr)            \
           || ((SEC) == bfd_com_section_ptr)            \
           || ((SEC) == bfd_ind_section_ptr))

         /* Macros to handle insertion and deletion of a bfd's sections.  These
            only handle the list pointers, ie. do not adjust section_count,
            target_index etc.  */
         #define bfd_section_list_remove(ABFD, S) \
           do                                                   \
             {                                                  \
               asection *_s = S;                                \
               asection *_next = _s->next;                      \
               asection *_prev = _s->prev;                      \
               if (_prev)                                       \
                 _prev->next = _next;                           \
               else                                             \
                 (ABFD)->sections = _next;                      \
               if (_next)                                       \
                 _next->prev = _prev;                           \
               else                                             \
                 (ABFD)->section_last = _prev;                  \
             }                                                  \
           while (0)
         #define bfd_section_list_append(ABFD, S) \
           do                                                   \
             {                                                  \
               asection *_s = S;                                \
               bfd *_abfd = ABFD;                               \
               _s->next = NULL;                                 \
               if (_abfd->section_last)                         \
                 {                                              \
                   _s->prev = _abfd->section_last;              \
                   _abfd->section_last->next = _s;              \
                 }                                              \
               else                                             \
                 {                                              \
                   _s->prev = NULL;                             \
                   _abfd->sections = _s;                        \
                 }                                              \
               _abfd->section_last = _s;                        \
             }                                                  \
           while (0)
         #define bfd_section_list_prepend(ABFD, S) \
           do                                                   \
             {                                                  \
               asection *_s = S;                                \
               bfd *_abfd = ABFD;                               \
               _s->prev = NULL;                                 \
               if (_abfd->sections)                             \
                 {                                              \
                   _s->next = _abfd->sections;                  \
                   _abfd->sections->prev = _s;                  \
                 }                                              \
               else                                             \
                 {                                              \
                   _s->next = NULL;                             \
                   _abfd->section_last = _s;                    \
                 }                                              \
               _abfd->sections = _s;                            \
             }                                                  \
           while (0)
         #define bfd_section_list_insert_after(ABFD, A, S) \
           do                                                   \
             {                                                  \
               asection *_a = A;                                \
               asection *_s = S;                                \
               asection *_next = _a->next;                      \
               _s->next = _next;                                \
               _s->prev = _a;                                   \
               _a->next = _s;                                   \
               if (_next)                                       \
                 _next->prev = _s;                              \
               else                                             \
                 (ABFD)->section_last = _s;                     \
             }                                                  \
           while (0)
         #define bfd_section_list_insert_before(ABFD, B, S) \
           do                                                   \
             {                                                  \
               asection *_b = B;                                \
               asection *_s = S;                                \
               asection *_prev = _b->prev;                      \
               _s->prev = _prev;                                \
               _s->next = _b;                                   \
               _b->prev = _s;                                   \
               if (_prev)                                       \
                 _prev->next = _s;                              \
               else                                             \
                 (ABFD)->sections = _s;                         \
             }                                                  \
           while (0)
         #define bfd_section_removed_from_list(ABFD, S) \
           ((S)->next == NULL ? (ABFD)->section_last != (S) : (S)->next->prev != (S))

         #define BFD_FAKE_SECTION(SEC, FLAGS, SYM, NAME, IDX)                   \
           /* name, id,  index, next, prev, flags, user_set_vma,            */  \
           { NAME,  IDX, 0,     NULL, NULL, FLAGS, 0,                           \
                                                                                \
           /* linker_mark, linker_has_input, gc_mark, decompress_status,    */  \
              0,           0,                1,       0,                        \
                                                                                \
           /* segment_mark, sec_info_type, use_rela_p,                      */  \
              0,            0,             0,                                   \
                                                                                \
           /* sec_flg0, sec_flg1, sec_flg2, sec_flg3, sec_flg4, sec_flg5,   */  \
              0,        0,        0,        0,        0,        0,              \
                                                                                \
           /* vma, lma, size, rawsize, compressed_size, relax, relax_count, */  \
              0,   0,   0,    0,       0,               0,     0,               \
                                                                                \
           /* output_offset, output_section, alignment_power,               */  \
              0,             &SEC,           0,                                 \
                                                                                \
           /* relocation, orelocation, reloc_count, filepos, rel_filepos,   */  \
              NULL,       NULL,        0,           0,       0,                 \
                                                                                \
           /* line_filepos, userdata, contents, lineno, lineno_count,       */  \
              0,            NULL,     NULL,     NULL,   0,                      \
                                                                                \
           /* entsize, kept_section, moving_line_filepos,                    */ \
              0,       NULL,          0,                                        \
                                                                                \
           /* target_index, used_by_bfd, constructor_chain, owner,          */  \
              0,            NULL,        NULL,              NULL,               \
                                                                                \
           /* symbol,                    symbol_ptr_ptr,                    */  \
              (struct bfd_symbol *) SYM, &SEC.symbol,                           \
                                                                                \
           /* map_head, map_tail                                            */  \
              { NULL }, { NULL }                                                \
             }