[PATCH v2] MIPS: Allow compressed images to be loaded at any address

From: Alban
Date: Mon Feb 13 2017 - 15:38:39 EST

From: Alban Bedel <albeu@xxxxxxx>

Compressed images (vmlinuz.bin) have to be loaded at a specific
address that differ from the address normaly used for vmlinux.bin.
This is because the decompressor just write its output at the address
vmlinux.bin should be loaded at, and it shouldn't overwrite itself.
This limitation mean that the bootloader must be configured differently
when loading a vmlinux.bin or a vmlinuz.bin image, this is annoying
and a source of error.

To workaround this we extend the compressed loader to cope with being
loaded at (nearly) any address. During the early init a jump is used
to compute the offset between the current address and the linked
address, if they differ the whole image is first copied to the linked
address before proceeding.

Some load address won't work, for example if there is an overlap with
the range where vmlinuz.bin should be loaded. However for the typical
case of using the vmlinux.bin address that won't be the case.

Signed-off-by: Alban Bedel <albeu@xxxxxxx>
Suggested-by: Jonas Gorski <jonas.gorski@xxxxxxxxx>
v2: * Rework the code as suggested by Jonas Gorski to autodetect the
load address and remove the need for a Kconfig option.
arch/mips/boot/compressed/head.S | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/mips/boot/compressed/head.S b/arch/mips/boot/compressed/head.S
index 409cb48..3c25a96 100644
--- a/arch/mips/boot/compressed/head.S
+++ b/arch/mips/boot/compressed/head.S
@@ -25,6 +25,29 @@ start:
move s2, a2
move s3, a3

+ /* Get the offset between the current address and linked address */
+ PTR_LA t0, reloc_label
+ bal reloc_label
+ nop
+ subu t0, ra, t0
+ /* If there is no offset no reloc is needed */
+ beqz t0, clear_bss
+ nop
+ /* Move the text, data section and DTB to the correct address */
+ PTR_LA a0, .text
+ addu a1, t0, a0
+ PTR_LA a2, _edata
+ lw a3, 0(a1)
+ sw a3, 0(a0)
+ addiu a0, a0, 4
+ bne a2, a0, copy_vmlinuz
+ addiu a1, a1, 4
/* Clear BSS */
PTR_LA a0, _edata
PTR_LA a2, _end