[PATCH 3/6] ARM: zImage: make sure appended DTB doesn't get overwritten by kernel .bss
Nicolas Pitre
nico at fluxnic.net
Wed Sep 14 01:41:43 EDT 2011
From: Nicolas Pitre <nicolas.pitre at linaro.org>
The appended DTB gets relocated with the decompressor code to get out
of the way of the decompressed kernel. However the kernel's .bss section
may be larger than the relocated code and data, and then the DTB gets
overwritten. Let's make sure the relocation takes care of moving zImage
far enough so no such conflict with .bss occurs.
Thanks to Tony Lindgren <tony at atomide.com> for figuring out this issue.
While at it, let's clean up the code a bit so that the wont_overwrite
symbol is used while determining if a conflict exists, making the above
change more precise as well as eliminating some ARM/THUMB alternates.
Signed-off-by: Nicolas Pitre <nicolas.pitre at linaro.org>
Acked-by: Tony Lindgren <tony at atomide.com>
---
arch/arm/boot/compressed/Makefile | 3 +++
arch/arm/boot/compressed/head.S | 19 +++++++++++++++----
2 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 0c74a6fab9..4867647b97 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -104,6 +104,9 @@ endif
ccflags-y := -fpic -fno-builtin
asflags-y := -Wa,-march=all
+# Supply kernel BSS size to the decompressor via a linker symbol.
+KBSS_SZ = $(shell size $(obj)/../../../../vmlinux | awk 'END{print $$3}')
+LDFLAGS_vmlinux = --defsym _kernel_bss_size=$(KBSS_SZ)
# Supply ZRELADDR to the decompressor via a linker symbol.
ifneq ($(CONFIG_AUTO_ZRELADDR),y)
LDFLAGS_vmlinux += --defsym zreladdr=$(ZRELADDR)
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 3ce5738ddb..ba5c552f8c 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -248,6 +248,18 @@ restart: adr r0, LC0
mov r8, r6 @ use the appended device tree
+ /*
+ * Make sure that the DTB doesn't end up in the final
+ * kernel's .bss area. To do so, we adjust the decompressed
+ * kernel size to compensate if that .bss size is larger
+ * than the relocated code.
+ */
+ ldr r5, =_kernel_bss_size
+ adr r1, wont_overwrite
+ sub r1, r6, r1
+ subs r1, r5, r1
+ addhi r9, r9, r1
+
/* Get the dtb's size */
ldr r5, [r6, #4]
#ifndef __ARMEB__
@@ -276,15 +288,14 @@ dtb_check_done:
* r10 = end of this image, including bss/stack/malloc space if non XIP
* We basically want:
* r4 - 16k page directory >= r10 -> OK
- * r4 + image length <= current position (pc) -> OK
+ * r4 + image length <= address of wont_overwrite -> OK
*/
add r10, r10, #16384
cmp r4, r10
bhs wont_overwrite
add r10, r4, r9
- ARM( cmp r10, pc )
- THUMB( mov lr, pc )
- THUMB( cmp r10, lr )
+ adr r9, wont_overwrite
+ cmp r10, r9
bls wont_overwrite
/*
--
1.7.7-rc0
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