section

Defines a section of an ELF (Executable and Linkable Format) object file.

  .section name [,alignment [,type [,flags]]]

Parameters

name

Name of the section.

alignment

Alignment boundary.

type

Numeric value for the ELF section type, per ELF Section Header Types (SHT) . The default type value is 1: (SHT_PROGBITS).

flags

Numeric value for the ELF section flags, per ELF Section Header Flags (SHF) . The default flags value is 0x00000002, 0x00000001: (SHF_ALLOC+SHF_WRITE).

Table 1. ELF Section Header Types (SHT)
Type	Name	Meaning
0	NULL	Section header is inactive.
1	PROGBITS	Section contains information that the program defines.
2	SYMTAB	Section contains a symbol table.
3	STRTAB	Section contains a string table.
4	RELA	Section contains relocation entries with explicit addends.
5	HASH	Section contains a symbol hash table.
6	DYNAMIC	Section contains information used for dynamic linking.
7	NOTE	Section contains information that marks the file, often for compatibility purposes between programs.
8	NOBITS	Section occupies no space in the object file.
9	REL	Section contains relocation entries without explicit addends.
10	SHLIB	Section has unspecified semantics, so does not conform to the Application Binary Interface (ABI) standard.
11	DYNSYM	Section contains a minimal set of symbols for dynamic linking.

Table 2. ELF Section Header Flags (SHF)
Flag	Name	Meaning
0x00000001	WRITE	Section contains data that is writable during execution.
0x00000002	ALLOC	Section occupies memory during execution.
0x00000004	EXECINSTR	Section contains executable machine instructions.
0xF0000000	MASKPROC	Bits this mask specifies are reserved for processor-specific purposes.

Remark

Use this directive to create arbitrary relocatable sections, including sections to be loaded at an absolute address.

Possiblesyntaxforms

The section directive accepts a number of different syntax forms, partly for convenience and partly for compatibility with other assemblers. A section declaration requires four pieces of information: a section name, alignment, ELF section type (for example, SHT_PROGBITS) and ELF section flags (for example, SHF_ALLOC+SHF_EXECINSTR).

The possible syntax forms are as follows:

Specify built-in section name.

.section text

This example specifies a built-in section name text. Equivalently, .text is also a valid syntax form.

Built-in Section names with their ELF Types and Flags provides a list of all the possible values, together with their ELF types and ELF Section Header Flags.

Table 3. Built-in Section names with their ELF Types and Flags
Name	ELF Type	ELF Flag
.text	SHT_PROGBITS	SHF_ALLOC+SHF_EXECINSTR
.data	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE
.rodata	SHT_PROGBITS	SHF_ALLOC
.bss	SHT_NOBITS	SHF_ALLOC+SHF_WRITE
.sdata	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE
.sdata0	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE
.sdata2	SHT_PROGBITS	SHF_ALLOC
.sbss	SHT_NOBITS	SHF_ALLOC+SHF_WRITE
.sbss0	SHT_NOBITS	SHF_ALLOC+SHF_WRITE
.sbss2	SHT_PROGBITS	SHF_ALLOC
.debug	SHT_PROGBITS	0
.text_vle	SHT_PROGBITS	SHF_ALLOC+SHF_EXECINSTR+ SHF_PE_EXECINSTR
.PPC.EMB.sdata0	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE
.PPC.EMB.sbss0	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE

In general, .text is for instructions, .data for initialised data, .rodata for read-only data (constants) and .bss for uninitialised data. The additional forms like .sdata are for small data areas. The built-in section names are architecture-specific, and are intended to make access to data more efficient. The alignment used for these sections is architecture-specific and is usually 4.

Specify your own section name but get the attributes of the built-in section type.
.section mySection,text

This example is equivalent to writing .text except that the section will be called mySection.
Specify the alignment, and optionally the ELF type and flags.
.section name [,alignment [,type [,flags]]]

In the syntax above, if the alignment is not specified it defaults to 16. If the type or flags are not specified, the defaults are as follows:
- If the name parameter is a built-in section name, the type and the flags are taken as specified in the Built-in Section names with their ELF Types and Flags . For example, in the syntax form.section text,8 the type is SHT_PROGBITS and the flags value is SHF_ALLOC+SHF_EXECINSTR.
- In all other cases, the default type is SHT_PROGBITS and the default flags value is SHF_ALLOC+SHF_WRITE, corresponding to a writeable data section.

Specify the type and flags parameters in pre-defined characters, optionally in double quotes.

.section mySection,4,"rx" or .section mySection,4,rx

The values are additive. For example, rx is equivalent to SHF_ALLOC+SHF_WRITE+SHF_EXECINSTR

Note: If the syntax doesn't specify a type it defaults to SHT_PROGBITS

Characters and their corresponding ELF Type and ELF Flags provides a list of all the possible characters and their corresponding ELF Type and ELF Flags.

Table 4. Characters and their corresponding ELF Type and ELF Flags
Character	ELF Type	ELF Flag
b	SHT_NOBITS	SHF_ALLOC+SHF_WRITE
c	SHT_PROGBITS	SHF_ALLOC+SHF_EXECINSTR
d	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE
m	SHT_PROGBITS	SHF_ALLOC+SHF_WRITE+ SHF_EXECINSTR
r	0	SHF_ALLOC
w	0	SHF_ALLOC+SHF_WRITE
x	0	SHF_ALLOC+SHF_EXECINSTR