Each load object, whether an executable or a shared object, contains a text section with the instructions generated by the compiler, a data section for data, and various symbol tables. All load objects must contain an ELF symbol table, which gives the names and addresses of all the globally-known functions in that object. Load objects compiled with the -g option contain additional symbolic information, which can augment the ELF symbol table and provide information about functions that are not global, additional information about object modules from which the functions came, and line number information relating addresses to source lines.
The term function is used to describe a set of instructions that represent a high-level operation described in the source code. The term covers subroutines as used in Fortran, methods as used in C++ and the Java programming language, and the like. Functions are described cleanly in the source code, and normally their names appear in the symbol table representing a set of addresses; if the program counter is within that set, the program is executing within that function.
In principle, any address within the text segment of a load object can be mapped to a function. Exactly the same mapping is used for the leaf PC and all the other PCs on the call stack. Most of the functions correspond directly to the source model of the program. Some do not; these functions are described in the following sections.