bl31: Split into two separate memory regions
Some platforms are extremely memory constrained and must split BL31
between multiple non-contiguous areas in SRAM. Allow the NOBITS
sections (.bss, stacks, page tables, and coherent memory) to be placed
in a separate region of RAM from the loaded firmware image.
Because the NOBITS region may be at a lower address than the rest of
BL31, __RW_{START,END}__ and __BL31_{START,END}__ cannot include this
region, or el3_entrypoint_common would attempt to invalidate the dcache
for the entire address space. New symbols __NOBITS_{START,END}__ are
added when SEPARATE_NOBITS_REGION is enabled, and the dcached for the
NOBITS region is invalidated separately.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: Idedfec5e4dbee77e94f2fdd356e6ae6f4dc79d37
diff --git a/docs/design/firmware-design.rst b/docs/design/firmware-design.rst
index cae94b5..5fc1335 100644
--- a/docs/design/firmware-design.rst
+++ b/docs/design/firmware-design.rst
@@ -1500,6 +1500,11 @@
this NOBITS section, making the image unnecessarily bigger. Smaller images
allow faster loading from the FIP to the main memory.
+For BL31, a platform can specify an alternate location for NOBITS sections
+(other than immediately following PROGBITS sections) by setting
+``SEPARATE_NOBITS_REGION`` to 1 and defining ``BL31_NOBITS_BASE`` and
+``BL31_NOBITS_LIMIT``.
+
Linker scripts and symbols
~~~~~~~~~~~~~~~~~~~~~~~~~~