Runtime Linker

When creating a dynamic object that initiates dynamic linking, the link-editor adds a program header element of type PT_INTERP to an executable file. This element instructing the system to invoke the runtime linker as the program interpreter. exec(2) and the runtime linker cooperate to create the process image for the program.

The link-editor constructs various data for executable and shared object files that assist the runtime linker. These data reside in loadable segments, thus making the data available during execution. These segments include.

• A .dynamic section with type SHT_DYNAMIC that holds various data. The structure residing at the beginning of the section holds the addresses of other dynamic linking information.

• The .got and .plt sections with type SHT_PROGBITS that hold two separate tables: the global offset table and the procedure linkage table. Sections that follow, explain how the runtime linker uses and changes the tables to create memory images for object files.

• The .hash section with type SHT_HASH that holds a symbol hash table.

Shared objects can occupy virtual memory addresses that are different from the addresses that are recorded in the file's program header table. The runtime linker relocates the memory image, updating absolute addresses before the application gains control.