Segment Contents

An object file segment consists of one or more sections, though this fact is transparent to the program header. Whether the file segment holds one or many sections also is immaterial to program loading. Nonetheless, various data must be present for program execution, dynamic linking, and so on. The diagrams below illustrate segment contents in general terms. The order and membership of sections within a segment can vary; moreover, processor-specific constraints can alter the examples below.

Text segments contain read-only instructions and data, in sections described earlier in this chapter. Data segments contain writable data and instructions. See Table 7-17 for a list of all special sections. Use dump(1) to see which sections are in a particular executable file.

A PT_DYNAMIC program header element points at the .dynamic section, as explained in "Dynamic Section" and later. The .got and .plt sections also hold information related to position-independent code and dynamic linking.

The .plt can reside in a text or a data segment, depending on the processor. See "Global Offset Table (Processor-Specific)" and "Procedure Linkage Table (Processor-Specific)" for details.

As previously described on Table 7-12, the .bss section has the type SHT_NOBITS. Although it occupies no space in the file, it contributes to the segment's memory image. Normally, these uninitialized data reside at the end of the segment, thereby making p_memsz larger than p_filesz in the associated program header element.