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;
/* 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;
/* A unique sequence number. */
unsigned int id;
/* A unique section number which can be used by assembler to
distinguish different sections with the same section name. */
unsigned int section_id;
/* Which section in the bfd; 0..n-1 as sections are created in a bfd. */
unsigned int index;
/* 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 0x0
/* Tells the OS to allocate space for this section when loading.
This is clear for a section containing debug information only. */
#define SEC_ALLOC 0x1
/* Tells the OS to load the section from the file when loading.
This is clear for a .bss section. */
#define SEC_LOAD 0x2
/* The section contains data still to be relocated, so there is
some relocation information too. */
#define SEC_RELOC 0x4
/* A signal to the OS that the section contains read only data. */
#define SEC_READONLY 0x8
/* The section contains code only. */
#define SEC_CODE 0x10
/* The section contains data only. */
#define SEC_DATA 0x20
/* The section will reside in ROM. */
#define SEC_ROM 0x40
/* 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 0x80
/* 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's size is fixed. Generic linker code will not
recalculate it and it is up to whoever has set this flag to
get the size right. */
#define SEC_FIXED_SIZE 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 contains a section ID to distinguish different
sections with the same section name. */
#define SEC_ASSEMBLER_SECTION_ID 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
/* Indicate that section has the purecode flag set. */
#define SEC_ELF_PURECODE 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
/* This section has the SHF_X86_64_LARGE flag. This is ELF x86-64 only. */
#define SEC_ELF_LARGE 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
/* This section contains vliw code. This is for Toshiba MeP only. */
#define SEC_MEP_VLIW 0x20000000
/* All symbols, sizes and relocations in this section are octets
instead of bytes. Required for DWARF debug sections as DWARF
information is organized in octets, not bytes. */
#define SEC_ELF_OCTETS 0x40000000
/* 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_ZLIB 2
#define DECOMPRESS_SECTION_ZSTD 3
/* 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
#define SEC_INFO_TYPE_EH_FRAME_ENTRY 6
#define SEC_INFO_TYPE_SFRAME 7
/* 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;
/* 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;
/* 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;
/* The alignment requirement of the section, as an exponent of 2 -
e.g., 3 aligns to 2^3 (or 8). */
unsigned int alignment_power;
/* 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. */
bfd_byte *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. The linked_to_symbol_name field is for ELF assembler
internal use. */
union {
struct bfd_link_order *link_order;
struct bfd_section *s;
const char *linked_to_symbol_name;
} map_head, map_tail;
/* Points to the output section this section is already assigned to,
if any. This is used when support for non-contiguous memory
regions is enabled. */
struct bfd_section *already_assigned;
/* Explicitly specified section type, if non-zero. */
unsigned int type;
} asection;