Allow for relocation to a region at the very end of the physical
address space (where the next address wraps to zero).
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Provide an implementation of the system memory map API based on the
system device tree, excluding any memory outside the size of the
accessible physical address space and defining an in-use region to
cover the relocated copy of iPXE and the system device tree.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The size of accessible physical address space will be required for the
runtime memory map, not just at relocation time. Make this size an
additional parameter to fdt_register() (matching the prototype for
fdt_relocate()), and record the value for future reference.
Note that we cannot simply store the limit in fdt_relocate() since it
is called before .data is writable and before .bss is zeroed.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
We do not currently describe the temporary page table or the temporary
stack as areas to be avoided during relocation of the iPXE image to a
new physical address.
Perform the copy of the iPXE image and zeroing of the .bss within
libprefix.S, after we have no futher use for the temporary page table
or the temporary initial stack. Perform the copy and registration of
the system device tree in C code after relocation is complete and the
new stack (within .bss) has been set up.
This provides a clean separation of responsibilities between the
RISC-V libprefix.S and the architecture-independent fdtmem.c. The
prefix is responsible only for relocating iPXE to the new physical
address returned from fdtmem_relocate(), and doesn't need to know or
care where fdtmem.c is planning to place the copy of the device tree.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
On startup, we may be running from read-only memory. We need to parse
the devicetree to obtain the system memory map, and identify a safe
location to which we can copy our own binary image along with a
stashed copy of the devicetree, and then transfer execution to this
new location.
Parsing the system memory map realistically requires running C code.
This in turn requires a small temporary stack, and some way to ensure
that symbol references are valid.
We first attempt to enable paging, to make the runtime virtual
addresses equal to the link-time virtual addresses. If this fails,
then we attempt to apply the compressed relocation records.
Assuming that one of these has worked (i.e. that either the CPU
supports paging or that our image started execution in writable
memory), then we call fdtmem_relocate() to parse the system memory map
to find a suitable relocation target address.
After the copy we disable paging, jump to the relocated copy,
re-enable paging, and reapply relocation records (if needed). At this
point, we have a full runtime environment, and can transfer control to
normal C code.
Provide this functionality as part of libprefix.S, since it is likely
to be shared by multiple prefixes.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Add code to parse the devicetree memory nodes, memory reservations
block, and reserved memory nodes to construct an ordered and
non-overlapping description of the system memory map, and use this to
identify a suitable address to which iPXE may be relocated at runtime.
We choose to place iPXE on a superpage boundary (as required by the
paging code), and to use the highest available address within
accessible memory. This mirrors the approach taken for x86 BIOS
builds, where we have long assumed that any image format that we might
need to support may require specific fixed addresses towards the
bottom of the memory map, but is very unlikely to require specific
fixed addresses towards the top of the memory map (since those
addresses may not exist, depending on the amount of installed RAM).
Signed-off-by: Michael Brown <mcb30@ipxe.org>
