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Diffstat (limited to 'docs/firmware-design.rst')
| -rw-r--r-- | docs/firmware-design.rst | 23 |
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diff --git a/docs/firmware-design.rst b/docs/firmware-design.rst index 79bdec98f..7cc74855d 100644 --- a/docs/firmware-design.rst +++ b/docs/firmware-design.rst @@ -2336,6 +2336,29 @@ implement: SUBSCRIBE_TO_EVENT(foo, foo_handler); + +Reclaiming the BL31 initialization code +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A significant amount of the code used for the initialization of BL31 is never +needed again after boot time. In order to reduce the runtime memory +footprint, the memory used for this code can be reclaimed after initialization +has finished and be used for runtime data. + +The build option ``RECLAIM_INIT_CODE`` can be set to mark this boot time code +with a ``.text.init.*`` attribute which can be filtered and placed suitably +within the BL image for later reclaimation by the platform. The platform can +specify the fiter and the memory region for this init section in BL31 via the +plat.ld.S linker script. For example, on the FVP, this section is placed +overlapping the secondary CPU stacks so that after the cold boot is done, this +memory can be reclaimed for the stacks. The init memory section is initially +mapped with ``RO``, ``EXECUTE`` attributes. After BL31 initilization has +completed, the FVP changes the attributes of this section to ``RW``, +``EXECUTE_NEVER`` allowing it to be used for runtime data. The memory attributes +are changed within the ``bl31_plat_runtime_setup`` platform hook. The init +section section can be reclaimed for any data which is accessed after cold +boot initialization and it is upto the platform to make the decision. + Performance Measurement Framework --------------------------------- |