From 4f79a5dd7c3e316e2230dc0ee665c40a39023a81 Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Mon, 29 Nov 2010 19:43:24 +0100 Subject: ARM: 6500/1: Thumb-2: Correct data alignment for CONFIG_THUMB2_KERNEL in kernel/head.S 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 Signed-off-by: Dave Martin Acked-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/kernel/head.S | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/arm/kernel/head.S') diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S index dd6b369ac69..591c097c89a 100644 --- a/arch/arm/kernel/head.S +++ b/arch/arm/kernel/head.S @@ -262,6 +262,7 @@ __create_page_tables: mov pc, lr ENDPROC(__create_page_tables) .ltorg + .align __enable_mmu_loc: .long . .long __enable_mmu @@ -308,6 +309,8 @@ ENTRY(__secondary_switched) b secondary_start_kernel ENDPROC(__secondary_switched) + .align + .type __secondary_data, %object __secondary_data: .long . @@ -413,6 +416,7 @@ __fixup_smp_on_up: mov pc, lr ENDPROC(__fixup_smp) + .align 1: .word . .word __smpalt_begin .word __smpalt_end -- cgit v1.2.3-18-g5258 From a75e5248c51af1eaeed936be6bd3497b93f09685 Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Mon, 29 Nov 2010 19:43:28 +0100 Subject: ARM: 6504/1: Thumb-2: Fix long-distance conditional branches in head.S for Thumb-2. The 32-bit conditional branches in Thumb-2 have a shorter range (+/-512K) than their ARM counterparts (+/-32MB). The linker does not currently generate trampolines to extend the range of these Thumb-2 conditional branches, resulting in link errors when vmlinux is sufficiently large, e.g.: head.o:(.text+0x464): relocation truncated to fit: R_ARM_THM_JUMP19 This patch forces the longer-range, unconditional branch encoding by use of an explicit IT instruction. The resulting branches are triggered on the same conditions as before. Signed-off-by: Dave Martin Signed-off-by: Russell King --- arch/arm/kernel/head.S | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/arm/kernel/head.S') diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S index 591c097c89a..6bd82d25683 100644 --- a/arch/arm/kernel/head.S +++ b/arch/arm/kernel/head.S @@ -85,9 +85,11 @@ ENTRY(stext) mrc p15, 0, r9, c0, c0 @ get processor id bl __lookup_processor_type @ r5=procinfo r9=cpuid movs r10, r5 @ invalid processor (r5=0)? + THUMB( it eq ) @ force fixup-able long branch encoding beq __error_p @ yes, error 'p' bl __lookup_machine_type @ r5=machinfo movs r8, r5 @ invalid machine (r5=0)? + THUMB( it eq ) @ force fixup-able long branch encoding beq __error_a @ yes, error 'a' bl __vet_atags #ifdef CONFIG_SMP_ON_UP @@ -283,6 +285,7 @@ ENTRY(secondary_startup) bl __lookup_processor_type movs r10, r5 @ invalid processor? moveq r0, #'p' @ yes, error 'p' + THUMB( it eq ) @ force fixup-able long branch encoding beq __error_p /* -- cgit v1.2.3-18-g5258