Depex FAQ - lersek/edk2 GitHub Wiki

Table of Contents Frequently asked questions about Depex How is the Dependency expression (depex) generated, and what is is the relationship with libraries? Are dependencies static, or determined at execution time? What are 'a priori' files?

A) Dependency expressions are generated based on info from the [DEPEX] section of a module's .inf file.

B) The module .inf lists the library classes it depends. Those library classes are cross-referenced through the platform .dsc file to determine which library instances are needed to complete the link of the module. If the libraries also have [DEPEX] sections, those are “and-ed” with the modules.

C) [EDK] did not have the concept of a Library Class – there were just libraries to link against. EDK I used the depx source file method with libraries. The developer’s job is easier in EDK II, since they don’t have consider inner dependencies on libraries.

D) To see the list of dependencies, use “build -Y DEPEX” to generate a DEPEX report.

DEPEX is determined at execution time. It is also possible to use events to create a runtime dependency behavior, but this is a matter of individual implementation.

The 'a priori' file is a special file that complements the dependency expression mechanism of PEI or DXE by stipulating a series of modules which need be dispatched in a prescribed order. This is an optional file, which provides a greater degree of flexibility in platform firmware. In general, the 'a priori' file is not required for most platform porting projects.