Sections

An object file's section header table lets one locate all the file's sections. The section header table is an array of Elf32_Shdr or Elf64_Shdr structures as described below. A section header table index is a subscript into this array. The ELF header's e_shoff member gives the byte offset from the beginning of the file to the section header table. e_shnum normally tells how many entries the section header table contains. e_shentsize gives the size in bytes of each entry.

If the number of sections is greater than or equal to SHN_LORESERVE (0xff00), e_shnum has the value SHN_UNDEF (0) and the actual number of section header table entries is contained in the sh_size field of the section header at index 0 (otherwise, the sh_size member of the initial entry contains 0).

Some section header table indexes are reserved in contexts where index size is restricted, for example, the st_shndx member of a symbol table entry and the e_shnum and e_shstrndx members of the ELF header. In such contexts, the reserved values do not represent actual sections in the object file. Also in such contexts, an escape value indicates that the actual section index is to be found elsewhere, in a larger field.


Figure 4-7: Special Section Indexes

Name Value
SHN_UNDEF 0
SHN_LORESERVE 0xff00
SHN_LOPROC 0xff00
SHN_HIPROC 0xff1f
SHN_LOOS 0xff20
SHN_HIOS 0xff3f
SHN_ABS 0xfff1
SHN_COMMON 0xfff2
SHN_XINDEX 0xffff
SHN_HIRESERVE 0xffff


SHN_UNDEF
This value marks an undefined, missing, irrelevant, or otherwise meaningless section reference. For example, a symbol ``defined'' relative to section number SHN_UNDEF is an undefined symbol.

NOTE: Although index 0 is reserved as the undefined value, the section header table contains an entry for index 0. If the e_shnum member of the ELF header says a file has 6 entries in the section header table, they have the indexes 0 through 5. The contents of the initial entry are specified later in this section.

SHN_LORESERVE
This value specifies the lower bound of the range of reserved indexes.

SHN_LOPROC through SHN_HIPROC
Values in this inclusive range are reserved for processor-specific semantics.

SHN_LOOS through SHN_HIOS
Values in this inclusive range are reserved for operating system-specific semantics.

SHN_ABS
This value specifies absolute values for the corresponding reference. For example, symbols defined relative to section number SHN_ABS have absolute values and are not affected by relocation.

SHN_COMMON
Symbols defined relative to this section are common symbols, such as FORTRAN COMMON or unallocated C external variables.

SHN_XINDEX
This value is an escape value. It indicates that the actual section header index is too large to fit in the containing field and is to be found in another location (specific to the structure where it appears).

SHN_HIRESERVE
This value specifies the upper bound of the range of reserved indexes. The system reserves indexes between SHN_LORESERVE and SHN_HIRESERVE, inclusive; the values do not reference the section header table. The section header table does not contain entries for the reserved indexes.

Sections contain all information in an object file except the ELF header, the program header table, and the section header table. Moreover, object files' sections satisfy several conditions.

A section header has the following structure.
Figure 4-8: Section Header

typedef struct { Elf32_Word sh_name; Elf32_Word sh_type; Elf32_Word sh_flags; Elf32_Addr sh_addr; Elf32_Off sh_offset; Elf32_Word sh_size; Elf32_Word sh_link; Elf32_Word sh_info; Elf32_Word sh_addralign; Elf32_Word sh_entsize; } Elf32_Shdr; typedef struct { Elf64_Word sh_name; Elf64_Word sh_type; Elf64_Xword sh_flags; Elf64_Addr sh_addr; Elf64_Off sh_offset; Elf64_Xword sh_size; Elf64_Word sh_link; Elf64_Word sh_info; Elf64_Xword sh_addralign; Elf64_Xword sh_entsize; } Elf64_Shdr;


sh_name
This member specifies the name of the section. Its value is an index into the section header string table section [see ``String Table'' below], giving the location of a null-terminated string.

sh_type
This member categorizes the section's contents and semantics. Section types and their descriptions appear below.

sh_flags
Sections support 1-bit flags that describe miscellaneous attributes. Flag definitions appear below.

sh_addr
If the section will appear in the memory image of a process, this member gives the address at which the section's first byte should reside. Otherwise, the member contains 0.

sh_offset
This member's value gives the byte offset from the beginning of the file to the first byte in the section. One section type, SHT_NOBITS described below, occupies no space in the file, and its sh_offset member locates the conceptual placement in the file.

sh_size
This member gives the section's size in bytes. Unless the section type is SHT_NOBITS, the section occupies sh_size bytes in the file. A section of type SHT_NOBITS may have a non-zero size, but it occupies no space in the file.

sh_link
This member holds a section header table index link, whose interpretation depends on the section type. A table below describes the values.

sh_info
This member holds extra information, whose interpretation depends on the section type. A table below describes the values. If the sh_flags field for this section header includes the attribute SHF_INFO_LINK, then this member represents a section header table index.

sh_addralign
Some sections have address alignment constraints. For example, if a section holds a doubleword, the system must ensure doubleword alignment for the entire section. The value of sh_addr must be congruent to 0, modulo the value of sh_addralign. Currently, only 0 and positive integral powers of two are allowed. Values 0 and 1 mean the section has no alignment constraints.

sh_entsize
Some sections hold a table of fixed-size entries, such as a symbol table. For such a section, this member gives the size in bytes of each entry. The member contains 0 if the section does not hold a table of fixed-size entries.

A section header's sh_type member specifies the section's semantics.


Figure 4-9: Section Types,sh_type

Name Value
SHT_NULL 0
SHT_PROGBITS 1
SHT_SYMTAB 2
SHT_STRTAB 3
SHT_RELA 4
SHT_HASH 5
SHT_DYNAMIC 6
SHT_NOTE 7
SHT_NOBITS 8
SHT_REL 9
SHT_SHLIB 10
SHT_DYNSYM 11
SHT_INIT_ARRAY 14
SHT_FINI_ARRAY 15
SHT_PREINIT_ARRAY 16
SHT_GROUP 17
SHT_SYMTAB_SHNDX 18
SHT_LOOS 0x60000000
SHT_HIOS 0x6fffffff
SHT_LOPROC 0x70000000
SHT_HIPROC 0x7fffffff
SHT_LOUSER 0x80000000
SHT_HIUSER 0xffffffff


SHT_NULL
This value marks the section header as inactive; it does not have an associated section. Other members of the section header have undefined values.

SHT_PROGBITS
The section holds information defined by the program, whose format and meaning are determined solely by the program.

SHT_SYMTAB and SHT_DYNSYM
These sections hold a symbol table. Currently, an object file may have only one section of each type, but this restriction may be relaxed in the future. Typically, SHT_SYMTAB provides symbols for link editing, though it may also be used for dynamic linking. As a complete symbol table, it may contain many symbols unnecessary for dynamic linking. Consequently, an object file may also contain a SHT_DYNSYM section, which holds a minimal set of dynamic linking symbols, to save space. See ``Symbol Table'' below for details.

SHT_STRTAB
The section holds a string table. An object file may have multiple string table sections. See ``String Table'' below for details.

SHT_RELA
The section holds relocation entries with explicit addends, such as type Elf32_Rela for the 32-bit class of object files or type Elf64_Rela for the 64-bit class of object files. An object file may have multiple relocation sections. ``Relocation'' below for details.

SHT_HASH
The section holds a symbol hash table. Currently, an object file may have only one hash table, but this restriction may be relaxed in the future. See ``Hash Table'' in the Chapter 5 for details.

SHT_DYNAMIC
The section holds information for dynamic linking. Currently, an object file may have only one dynamic section, but this restriction may be relaxed in the future. See ``Dynamic Section'' in Chapter 5 for details.

SHT_NOTE
The section holds information that marks the file in some way. See ``Note Section'' in Chapter 5 for details.

SHT_NOBITS
A section of this type occupies no space in the file but otherwise resembles SHT_PROGBITS. Although this section contains no bytes, the sh_offset member contains the conceptual file offset.

SHT_REL
The section holds relocation entries without explicit addends, such as type Elf32_Rel for the 32-bit class of object files or type Elf64_Rel for the 64-bit class of object files. An object file may have multiple relocation sections. See ``Relocation'' below for details.

SHT_SHLIB
This section type is reserved but has unspecified semantics.

SHT_INIT_ARRAY
This section contains an array of pointers to initialization functions, as described in ``Initialization and Termination Functions'' in Chapter 5. Each pointer in the array is taken as a parameterless procedure with a void return.

SHT_FINI_ARRAY
This section contains an array of pointers to termination functions, as described in ``Initialization and Termination Functions'' in Chapter 5. Each pointer in the array is taken as a parameterless procedure with a void return.

SHT_PREINIT_ARRAY
This section contains an array of pointers to functions that are invoked before all other initialization functions, as described in ``Initialization and Termination Functions'' in Chapter 5. Each pointer in the array is taken as a parameterless procedure with a void return.

SHT_GROUP
This section defines a section group. A section group is a set of sections that are related and that must be treated specially by the linker (see below for further details). Sections of type SHT_GROUP may appear only in relocatable objects (objects with the ELF header e_type member set to ET_REL). The section header table entry for a group section must appear in the section header table before the entries for any of the sections that are members of the group.

SHT_SYMTAB_SHNDX
This section is associated with a section of type SHT_SYMTAB and is required if any of the section header indexes referenced by that symbol table contain the escape value SHN_XINDEX. The section is an array of Elf32_Word values. Each value corresponds one to one with a symbol table entry and appear in the same order as those entries. The values represent the section header indexes against which the symbol table entries are defined. Only if corresponding symbol table entry's st_shndx field contains the escape value SHN_XINDEX will the matching Elf32_Word hold the actual section header index; otherwise, the entry must be SHN_UNDEF (0).

SHT_LOOS through SHT_HIOS
Values in this inclusive range are reserved for operating system-specific semantics.

SHT_LOPROC through SHT_HIPROC
Values in this inclusive range are reserved for processor-specific semantics.

SHT_LOUSER
This value specifies the lower bound of the range of indexes reserved for application programs.

SHT_HIUSER
This value specifies the upper bound of the range of indexes reserved for application programs. Section types between SHT_LOUSER and SHT_HIUSER may be used by the application, without conflicting with current or future system-defined section types.

Other section type values are reserved. As mentioned before, the section header for index 0 (SHN_UNDEF) exists, even though the index marks undefined section references. This entry holds the following.


Figure 4-10: Section Header Table Entry:Index 0

Name Value Note
sh_name 0 No name
sh_type SHT_NULL Inactive
sh_flags 0 No flags
sh_addr 0 No address
sh_offset 0 No offset
sh_size Unspecified If non-zero, the actual number of section header entries
sh_link Unspecified If non-zero, the index of the section header string table section
sh_info 0 No auxiliary information
sh_addralign 0 No alignment
sh_entsize 0 No entries


A section header's sh_flags member holds 1-bit flags that describe the section's attributes. Defined values appear in the following table; other values are reserved.


Figure 4-11: Section Attribute Flags

Name Value
SHF_WRITE 0x1
SHF_ALLOC 0x2
SHF_EXECINSTR 0x4
SHF_MERGE 0x10
SHF_STRINGS 0x20
SHF_INFO_LINK 0x40
SHF_LINK_ORDER 0x80
SHF_OS_NONCONFORMING 0x100
SHF_GROUP 0x200
SHF_TLS 0x400
SHF_COMPRESSED 0x800
SHF_MASKOS 0x0ff00000
SHF_MASKPROC 0xf0000000


If a flag bit is set in sh_flags, the attribute is ``on'' for the section. Otherwise, the attribute is ``off'' or does not apply. Undefined attributes are set to zero.

SHF_WRITE
The section contains data that should be writable during process execution.

SHF_ALLOC
The section occupies memory during process execution. Some control sections do not reside in the memory image of an object file; this attribute is off for those sections.

SHF_EXECINSTR
The section contains executable machine instructions.

SHF_MERGE
The data in the section may be merged to eliminate duplication. Unless the SHF_STRINGS flag is also set, the data elements in the section are of a uniform size. The size of each element is specified in the section header's sh_entsize field. If the SHF_STRINGS flag is also set, the data elements consist of null-terminated character strings. The size of each character is specified in the section header's sh_entsize field.

Each element in the section is compared against other elements in sections with the same name, type and flags. Elements that would have identical values at program run-time may be merged. Relocations referencing elements of such sections must be resolved to the merged locations of the referenced values. Note that any relocatable values, including values that would result in run-time relocations, must be analyzed to determine whether the run-time values would actually be identical. An ABI-conforming object file may not depend on specific elements being merged, and an ABI-conforming link editor may choose not to merge specific elements.

SHF_STRINGS
The data elements in the section consist of null-terminated character strings. The size of each character is specified in the section header's sh_entsize field.

SHF_INFO_LINK
The sh_info field of this section header holds a section header table index.

SHF_LINK_ORDER
This flag adds special ordering requirements for link editors. The requirements apply if the sh_link field of this section's header references another section (the linked-to section). If this section is combined with other sections in the output file, it must appear in the same relative order with respect to those sections, as the linked-to section appears with respect to sections the linked-to section is combined with.


NOTE: A typical use of this flag is to build a table that references text or data sections in address order.

SHF_OS_NONCONFORMING
This section requires special OS-specific processing (beyond the standard linking rules) to avoid incorrect behavior. If this section has either an sh_type value or contains sh_flags bits in the OS-specific ranges for those fields, and a link editor processing this section does not recognize those values, then the link editor should reject the object file containing this section with an error.

SHF_GROUP
This section is a member (perhaps the only one) of a section group. The section must be referenced by a section of type SHT_GROUP. The SHF_GROUP flag may be set only for sections contained in relocatable objects (objects with the ELF header e_type member set to ET_REL). See below for further details.

SHF_TLS
This section holds Thread-Local Storage, meaning that each separate execution flow has its own distinct instance of this data. Implementations need not support this flag.

SHF_COMPRESSED
This flag identifies a section containing compressed data. SHF_COMPRESSED applies only to non-allocable sections, and cannot be used in conjunction with SHF_ALLOC. In addition, SHF_COMPRESSED cannot be applied to sections of type SHT_NOBITS.

All relocations to a compressed section specifiy offsets to the uncompressed section data. It is therefore necessary to decompress the section data before relocations can be applied. Each compressed section specifies the algorithm independently. It is permissible for different sections in a given ELF object to employ different compression algorithms.

Compressed sections begin with a compression header structure that identifies the compression algorithm.


Figure 4-12: Compression Header

typedef struct { Elf32_Word ch_type; Elf32_Word ch_size; Elf32_Word ch_addralign; } Elf32_Chdr; typedef struct { Elf64_Word ch_type; Elf64_Word ch_reserved; Elf64_Xword ch_size; Elf64_Xword ch_addralign; } Elf64_Chdr;


ch_type
This member specifies the compression algorithm. Supported algorithms and their descriptions are listed in the ELF Compression Types table below.

ch_size
This member provides the size in bytes of the uncompressed data. See sh_size.

ch_addralign
Specifies the required alignment for the uncompressed data. See sh_addralign.

The sh_size and sh_addralign fields of the section header for a compressed section reflect the requirements of the compressed section. The ch_size and ch_addralign fields in the compression header provide the corresponding values for the uncompressed data, thereby supplying the values that sh_size and sh_addralign would have had if the section had not been compressed.

The layout and interpretation of the data that follows the compression header is specific to each algorithm, and is defined below for each value of ch_type. This area may contain algorithm specific parameters and alignment padding in addition to compressed data bytes.

A compression header's ch_type member specifies the compression algoritm employed, as shown in the following table.


Figure 4-13: ELF Compression Types, ch_type

Name Value
ELFCOMPRESS_ZLIB 1
ELFCOMPRESS_LOOS 0x60000000
ELFCOMPRESS_HIOS 0x6fffffff
ELFCOMPRESS_LOPROC 0x70000000
ELFCOMPRESS_HIPROC 0x7fffffff


ELFCOMPRESS_ZLIB
The section data is compressed with the ZLIB algoritm. The compressed ZLIB data bytes begin with the byte immediately following the compression header, and extend to the end of the section. Additional documentation for ZLIB may be found at http://zlib.net.

ELFCOMPRESS_LOOS - ELFCOMPRESS_HIOS
Values in this inclusive range are reserved for operating system-specific semantics.

ELFCOMPRESS_LOPROC - ELF_COMPRESS_HIPROC
Values in this inclusive range are reserved for processor-specific semantics.

SHF_MASKOS
All bits included in this mask are reserved for operating system-specific semantics.

SHF_MASKPROC
All bits included in this mask are reserved for processor-specific semantics. If meanings are specified, the processor supplement explains them.

Two members in the section header, sh_link and sh_info, hold special information, depending on section type.


Figure 4-14: sh_link and sh_info Interpretation

sh_type sh_link sh_info
SHT_DYNAMIC The section header index of the string table used by entries in the section. 0
SHT_HASH The section header index of the symbol table to which the hash table applies. 0
SHT_REL
SHT_RELA
The section header index of the associated symbol table. The section header index of the section to which the relocation applies.
SHT_SYMTAB
SHT_DYNSYM
The section header index of the associated string table. One greater than the symbol table index of the last local symbol (binding STB_LOCAL).
SHT_GROUP The section header index of the associated symbol table. The symbol table index of an entry in the associated symbol table. The name of the specified symbol table entry provides a signature for the section group.
SHT_SYMTAB_SHNDX The section header index of the associated symbol table section. 0


Rules for Linking Unrecognized Sections

If a link editor encounters sections whose headers contain OS-specific values it does not recognize in the sh_type or sh_flags fields, the link editor should combine those sections as described below.

If the section's sh_flags bits include the attribute SHF_OS_NONCONFORMING, then the section requires special knowledge to be correctly processed, and the link editor should reject the object containing the section with an error.

Unrecognized sections that do not have the SHF_OS_NONCONFORMING attribute, are combined in a two-phase process. As the link editor combines sections using this process, it must honor the alignment constraints of the input sections (asserted by the sh_addralign field), padding between sections with zero bytes, if necessary, and producing a combination with the maximum alignment constraint of its component input sections.

  1. In the first phase, input sections that match in name, type and attribute flags should be concatenated into single sections. The concatenation order should satisfy the requirements of any known input section attributes (e.g, SHF_MERGE and SHF_LINK_ORDER). When not otherwise constrained, sections should be emitted in input order.
  2. In the second phase, sections should be assigned to segments or other units based on their attribute flags. Sections of each particular unrecognized type should be assigned to the same unit unless prevented by incompatible flags, and within a unit, sections of the same unrecognized type should be placed together if possible.

Non OS-specific processing (e.g. relocation) should be applied to unrecognized section types. An output section header table, if present, should contain entries for unknown sections. Any unrecognized section attribute flags should be removed.


NOTE: It is recommended that link editors follow the same two-phase ordering approach described above when linking sections of known types. Padding between such sections may have values different from zero, where appropriate.

Section Groups

Some sections occur in interrelated groups. For example, an out-of-line definition of an inline function might require, in addition to the section containing its executable instructions, a read-only data section containing literals referenced, one or more debugging information sections and other informational sections. Furthermore, there may be internal references among these sections that would not make sense if one of the sections were removed or replaced by a duplicate from another object. Therefore, such groups must be included or omitted from the linked object as a unit. A section cannot be a member of more than one group.

A section of type SHT_GROUP defines such a grouping of sections. The name of a symbol from one of the containing object's symbol tables provides a signature for the section group. The section header of the SHT_GROUP section specifies the identifying symbol entry, as described above: the sh_link member contains the section header index of the symbol table section that contains the entry. The sh_info member contains the symbol table index of the identifying entry. The sh_flags member of the section header contains 0. The name of the section (sh_name) is not specified.

The referenced signature symbol is not restricted. Its containing symbol table section need not be a member of the group, for example.

The section data of a SHT_GROUP section is an array of Elf32_Word entries. The first entry is a flag word. The remaining entries are a sequence of section header indices.

The following flags are currently defined:


Figure 4-15: Section Group Flags

Name Value
GRP_COMDAT 0x1
GRP_MASKOS 0x0ff00000
GRP_MASKPROC 0xf0000000


GRP_COMDAT
This is a COMDAT group. It may duplicate another COMDAT group in another object file, where duplication is defined as having the same group signature. In such cases, only one of the duplicate groups may be retained by the linker, and the members of the remaining groups must be discarded.

GRP_MASKOS
All bits included in this mask are reserved for operating system-specific semantics.

GRP_MASKPROC
All bits included in this mask are reserved for processor-specific semantics. If meanings are specified, the processor supplement explains them.

The section header indices in the SHT_GROUP section identify the sections that make up the group. Each such section must have the SHF_GROUP flag set in its sh_flags section header member. If the linker decides to remove the section group, it must remove all members of the group.


NOTE: This requirement is not intended to imply that special case behavior like removing debugging information requires removing the sections to which that information refers, even if they are part of the same group.

To facilitate removing a group without leaving dangling references and with only minimal processing of the symbol table, the following rules must be followed:

Special Sections

Various sections hold program and control information.

The following table shows sections that are used by the system and have the indicated types and attributes.


Figure 4-16: Special Sections

Name Type Attributes
.bss SHT_NOBITS SHF_ALLOC+SHF_WRITE
.comment SHT_PROGBITS none
.data SHT_PROGBITS SHF_ALLOC+SHF_WRITE
.data1 SHT_PROGBITS SHF_ALLOC+SHF_WRITE
.debug SHT_PROGBITS none
.dynamic SHT_DYNAMIC see below
.dynstr SHT_STRTAB SHF_ALLOC
.dynsym SHT_DYNSYM SHF_ALLOC
.fini SHT_PROGBITS SHF_ALLOC+SHF_EXECINSTR
.fini_array SHT_FINI_ARRAY SHF_ALLOC+SHF_WRITE
.got SHT_PROGBITS see below
.hash SHT_HASH SHF_ALLOC
.init SHT_PROGBITS SHF_ALLOC+SHF_EXECINSTR
.init_array SHT_INIT_ARRAY SHF_ALLOC+SHF_WRITE
.interp SHT_PROGBITS see below
.line SHT_PROGBITS none
.note SHT_NOTE none
.plt SHT_PROGBITS see below
.preinit_array SHT_PREINIT_ARRAY SHF_ALLOC+SHF_WRITE
.relname SHT_REL see below
.relaname SHT_RELA see below
.rodata SHT_PROGBITS SHF_ALLOC
.rodata1 SHT_PROGBITS SHF_ALLOC
.shstrtab SHT_STRTAB none
.strtab SHT_STRTAB see below
.symtab SHT_SYMTAB see below
.symtab_shndx SHT_SYMTAB_SHNDX see below
.tbss SHT_NOBITS SHF_ALLOC+SHF_WRITE+SHF_TLS
.tdata SHT_PROGBITS SHF_ALLOC+SHF_WRITE+SHF_TLS
.tdata1 SHT_PROGBITS SHF_ALLOC+SHF_WRITE+SHF_TLS
.text SHT_PROGBITS SHF_ALLOC+SHF_EXECINSTR


.bss
This section holds uninitialized data that contribute to the program's memory image. By definition, the system initializes the data with zeros when the program begins to run. The section occupies no file space, as indicated by the section type, SHT_NOBITS.

.comment
This section holds version control information.

.data and .data1
These sections hold initialized data that contribute to the program's memory image.

.debug
This section holds information for symbolic debugging. The contents are unspecified. All section names with the prefix .debug are reserved for future use in the ABI.

.dynamic
This section holds dynamic linking information. The section's attributes will include the SHF_ALLOC bit. Whether the SHF_WRITE bit is set is processor specific. See Chapter 5 for more information.

.dynstr
This section holds strings needed for dynamic linking, most commonly the strings that represent the names associated with symbol table entries. See Chapter 5 for more information.

.dynsym
This section holds the dynamic linking symbol table, as described in ``Symbol Table''. See Chapter 5 for more information.

.fini
This section holds executable instructions that contribute to the process termination code. That is, when a program exits normally, the system arranges to execute the code in this section.

.fini_array
This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section.

.got
This section holds the global offset table. See ``Coding Examples'' in Chapter 3, ``Special Sections'' in Chapter 4, and ``Global Offset Table'' in Chapter 5 of the processor supplement for more information.

.hash
This section holds a symbol hash table. See ``Hash Table'' in Chapter 5 for more information.

.init
This section holds executable instructions that contribute to the process initialization code. When a program starts to run, the system arranges to execute the code in this section before calling the main program entry point (called main for C programs).

.init_array
This section holds an array of function pointers that contributes to a single initialization array for the executable or shared object containing the section.

.interp
This section holds the path name of a program interpreter. If the file has a loadable segment that includes relocation, the sections' attributes will include the SHF_ALLOC bit; otherwise, that bit will be off. See Chapter 5 for more information.

.line
This section holds line number information for symbolic debugging, which describes the correspondence between the source program and the machine code. The contents are unspecified.

.note
This section holds information in the format that ``Note Section''. in Chapter 5 describes.

.plt
This section holds the procedure linkage table. See ``Special Sections'' in Chapter 4 and ``Procedure Linkage Table'' in Chapter 5 of the processor supplement for more information.

.preinit_array
This section holds an array of function pointers that contributes to a single pre-initialization array for the executable or shared object containing the section.

.relname and .relaname
These sections hold relocation information, as described in ``Relocation''. If the file has a loadable segment that includes relocation, the sections' attributes will include the SHF_ALLOC bit; otherwise, that bit will be off. Conventionally, name is supplied by the section to which the relocations apply. Thus a relocation section for .text normally would have the name .rel.text or .rela.text.

.rodata and .rodata1
These sections hold read-only data that typically contribute to a non-writable segment in the process image. See ``Program Header'' in Chapter 5 for more information.

.shstrtab
This section holds section names.

.strtab
This section holds strings, most commonly the strings that represent the names associated with symbol table entries. If the file has a loadable segment that includes the symbol string table, the section's attributes will include the SHF_ALLOC bit; otherwise, that bit will be off.

.symtab
This section holds a symbol table, as ``Symbol Table''. in this chapter describes. If the file has a loadable segment that includes the symbol table, the section's attributes will include the SHF_ALLOC bit; otherwise, that bit will be off.

.symtab_shndx
This section holds the special symbol table section index array, as described above. The section's attributes will include the SHF_ALLOC bit if the associated symbol table section does; otherwise that bit will be off.

.tbss
This section holds uninitialized thread-local data that contribute to the program's memory image. By definition, the system initializes the data with zeros when the data is instantiated for each new execution flow. The section occupies no file space, as indicated by the section type, SHT_NOBITS. Implementations need not support thread-local storage.

.tdata
This section holds initialized thread-local data that contributes to the program's memory image. A copy of its contents is instantiated by the system for each new execution flow. Implementations need not support thread-local storage.

.text
This section holds the ``text,'' or executable instructions, of a program.

Section names with a dot (.) prefix are reserved for the system, although applications may use these sections if their existing meanings are satisfactory. Applications may use names without the prefix to avoid conflicts with system sections. The object file format lets one define sections not shown in the previous list. An object file may have more than one section with the same name.

Section names reserved for a processor architecture are formed by placing an abbreviation of the architecture name ahead of the section name. The name should be taken from the architecture names used for e_machine. For instance .FOO.psect is the psect section defined by the FOO architecture. Existing extensions are called by their historical names.

Pre-existing Extensions
.sdata .tdesc
.sbss .lit4
.lit8 .reginfo
.gptab .liblist
.conflict


NOTE: For information on processor-specific sections, see the ABI supplement for the desired processor.
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