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Subject[PATCH 2/2] ARM: decompressor: relax the loading restriction of the decompressed kernel
Date
mov	r4, pc
and r4, r4, #0xf8000000 //truncated to 128MiB boundary
add r4, r4, #TEXT_OFFSET //PA(_start)

Currently, the decompressed kernel must be placed at the position: 128MiB
boundary + TEXT_OFFSET. This limitation is just because we masked PC with
0xf80000000. Actually, we can directly obtain PA(_start) by using formula
: VA(_start) + (PHYS_OFFSET - PAGE_OFFSET).

So the "PA(_start) - TEXT_OFFSET" can be 2MiB boundary, 1MiB boundary,
and so on.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
arch/arm/boot/compressed/head.S | 33 ++++++++++++++-------------------
1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 434a16982e344fe..e5ba2ad2ea4700f 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -255,26 +255,16 @@ not_angel:

#ifdef CONFIG_AUTO_ZRELADDR
/*
- * Find the start of physical memory. As we are executing
- * without the MMU on, we are in the physical address space.
- * We just need to get rid of any offset by aligning the
- * address.
- *
- * This alignment is a balance between the requirements of
- * different platforms - we have chosen 128MB to allow
- * platforms which align the start of their physical memory
- * to 128MB to use this feature, while allowing the zImage
- * to be placed within the first 128MB of memory on other
- * platforms. Increasing the alignment means we place
- * stricter alignment requirements on the start of physical
- * memory, but relaxing it means that we break people who
- * are already placing their zImage in (eg) the top 64MB
- * of this range.
+ * Find ZRELADDR (Address where the decompressed kernel was
+ * placed, usually == PHYS_OFFSET + TEXT_OFFSET). That's the
+ * start physical address of the text section, PA(_start).
+ * As we are executing without the MMU on, we are in the
+ * physical address space.
*/
- mov r4, pc
- and r4, r4, #0xf8000000
- /* Determine final kernel image address. */
- add r4, r4, #TEXT_OFFSET
+ adr r0, LC2
+ ldmia r0, {r3-r4}
+ sub r3, r0, r3 @ PHYS_OFFSET - PAGE_OFFSET
+ add r4, r4, r3 @ PA(_start)
#else
ldr r4, =zreladdr
#endif
@@ -660,6 +650,11 @@ LC1: .word .L_user_stack_end - LC1 @ sp
.word _edata - LC1 @ r6
.size LC1, . - LC1

+ .align 2
+ .type LC2, #object
+LC2: .word LC2
+ .word _start @ start VA of text section
+
.Lheadroom:
.word _end - restart + 16384 + 1024*1024

--
1.8.3

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