SLAU131Y October 2004 – June 2021
A subsection is created by creating a section with a colon in its name. Subsections are logical subdivisions of larger sections. Subsections are themselves sections and can be manipulated by the assembler and linker.
The assembler has no concept of subsections; to the assembler, the colon in the name is not special. The subsection .text:rts would be considered completely unrelated to its parent section .text, and the assembler will not combine subsections with their parent sections.
Subsections are used to keep parts of a section as distinct sections so that they can be separately manipulated. For instance, by placing each function and object in a uniquely-named subsection, the linker gets a finer-grained view of the section for memory placement and unused-function elimination.
By default, when the linker sees a SECTION directive in the linker command file like ".text", it will gather .text and all subsections of .text into one large output section named ".text". You can instead use the SECTION directive to control the subsection independently. See Section 9.6.5.1 for an example.
You can create subsections in the same way you create other user-named sections: by using the .sect or .usect directive.
The syntaxes for a subsection name are:
| symbol | .usect "section_name:subsection_name",size in bytes[, alignment] |
| .sect "section_name:subsection_name" |
A subsection is identified by the base section name followed by a colon and the name of the subsection. The subsection name may not contain any spaces.
A subsection can be allocated separately or grouped with other sections using the same base name. For example, you create a subsection called _func within the .text section:
.sect ".text:_func" Using the linker's SECTIONS directive, you can allocate .text:_func separately, or with all the .text sections.
You can create two types of subsections:
Subsections are placed in the same manner as sections. See Section 9.6.5 for information on the SECTIONS directive.