linux/arch/arm/kernel/relocate_kernel.S
Dave Martin bc8b57f08c ARM: 6497/1: kexec: Correct data alignment for CONFIG_THUMB2_KERNEL
Directives such as .long and .word do not magically cause the
assembler location counter to become aligned in gas.  As a result,
using these directives in code sections can result in misaligned
data words when building a Thumb-2 kernel (CONFIG_THUMB2_KERNEL).

This is a Bad Thing, since the ABI permits the compiler to assume
that fundamental types of word size or above are word- aligned when
accessing them from C.  If the data is not really word-aligned,
this can cause impaired performance and stray alignment faults in
some circumstances.

In general, the following rules should be applied when using data
word declaration directives inside code sections:

    * .quad and .double:
         .align 3

    * .long, .word, .single, .float:
         .align (or .align 2)

    * .short:
        No explicit alignment required, since Thumb-2
        instructions are always 2 or 4 bytes in size.
        immediately after an instruction.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-11-30 13:44:23 +00:00

88 lines
1.3 KiB
ArmAsm

/*
* relocate_kernel.S - put the kernel image in place to boot
*/
#include <asm/kexec.h>
.globl relocate_new_kernel
relocate_new_kernel:
ldr r0,kexec_indirection_page
ldr r1,kexec_start_address
/*
* If there is no indirection page (we are doing crashdumps)
* skip any relocation.
*/
cmp r0, #0
beq 2f
0: /* top, read another word for the indirection page */
ldr r3, [r0],#4
/* Is it a destination page. Put destination address to r4 */
tst r3,#1,0
beq 1f
bic r4,r3,#1
b 0b
1:
/* Is it an indirection page */
tst r3,#2,0
beq 1f
bic r0,r3,#2
b 0b
1:
/* are we done ? */
tst r3,#4,0
beq 1f
b 2f
1:
/* is it source ? */
tst r3,#8,0
beq 0b
bic r3,r3,#8
mov r6,#1024
9:
ldr r5,[r3],#4
str r5,[r4],#4
subs r6,r6,#1
bne 9b
b 0b
2:
/* Jump to relocated kernel */
mov lr,r1
mov r0,#0
ldr r1,kexec_mach_type
ldr r2,kexec_boot_atags
mov pc,lr
.align
.globl kexec_start_address
kexec_start_address:
.long 0x0
.globl kexec_indirection_page
kexec_indirection_page:
.long 0x0
.globl kexec_mach_type
kexec_mach_type:
.long 0x0
/* phy addr of the atags for the new kernel */
.globl kexec_boot_atags
kexec_boot_atags:
.long 0x0
relocate_new_kernel_end:
.globl relocate_new_kernel_size
relocate_new_kernel_size:
.long relocate_new_kernel_end - relocate_new_kernel