[RFC PATCH] arm: decompressor: initialize PIC offset base register for uClinux tools

[jonathan.austin@arm.com (Jonathan Austin)]

Before jumping to (position independent) C-code from the decompressor's
assembler world we set-up the C environment. This setup currently does not
set r9, which for arm-none-uclinux-uclibceabi should be the PIC offset base
register (IE should point to the beginning of the GOT).

Currently, therefore, in order to build working kernels that use the
decompressor it is necessary to use an arm-linux-gnueabi toolchain, or
similar. uClinux toolchains cause a Prefetch Abort to occur at the beginning
of the decompress_kernel function.

This patch allows uClinux toolchains to build bootable zImages by setting r9
to the beginning of the GOT when __uClinux__ is defined, allowing the
decompressor's C functions to work correctly.

Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
---

One other possibility would be to specify -mno-single-pic-base when building
the decompressor. This works around the problem, but forces the compiler to
generate less optimal code.

 arch/arm/boot/compressed/head.S |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index fe4d9c3..4491e75 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -410,6 +410,10 @@ wont_overwrite:
  *   sp  = stack pointer
  */
 		orrs	r1, r0, r5
+#ifdef __uClinux__
+		mov	r9, r11			@ PIC offset base register
+		addne	r9, r9, r0		@ Also needs relocating
+#endif
 		beq	not_relocated
 
 		add	r11, r11, r0
-- 
1.7.9.5