Hi Sami,<br />The ArmPkg implements two versions of the PeCoffExtraActionLib library at:<br />* ArmPkg/Library/DebugPeCoffExtraActionLib/DebugPeCoffExtraActionLib.inf<br />* ArmPkg/Library/RvdPeCoffExtraActionLib/RvdPeCoffExtraActionLib.inf<br /><br />They are explicitly built by being placed in a [Components] section of ArmPkg.dsc. The modules listed in the [Library] section are not guaranteed it to be built.<br /><br />From what I interpret, the [...]LibNull.inf modules are used as a empty shells so that when building a component, the libraries the component is dependent on are not not blame.<br />Thus, I think it is better to use the [...]LibNull.inf implementation in the Library section since it is available.<br /><br />This also means that in ArmPkg.dsc, we should maybe replace the libraries by their [...]LibNull.inf equivalent when possible, like:<br />CpuLib|MdePkg/Library/BaseCpuLib/BaseCpuLib.inf<br />being replaced by:<br />CpuLib|MdePkg/Library/BaseCpuLibNull/BaseCpuLibNull.inf<br /><br />Regards,<br />Pierre