[PATCH] arm64: remove __switch_data object from head.S

[PATCH] arm64: remove __switch_data object from head.S

[Ard Biesheuvel]

This removes the confusing __switch_data object from head.S,
and replaces it with standard PC-relative references to the
various symbols it encapsulates.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm64/kernel/head.S | 35 +++++++++++++----------------------
 1 file changed, 13 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 66675d27fea3..2afaf6b8e4e8 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -263,7 +263,7 @@ ENTRY(stext)
 	 * On return, the CPU will be ready for the MMU to be turned on and
 	 * the TCR will have been set.
 	 */
-	ldr	x27, __switch_data		// address to jump to after
+	ldr	x27, =__mmap_switched		// address to jump to after
 						// MMU has been enabled
 	adrp	lr, __enable_mmu		// return (PIC) address
 	add	lr, lr, #:lo12:__enable_mmu
@@ -397,37 +397,28 @@ __create_page_tables:
 ENDPROC(__create_page_tables)
 	.ltorg
 
-	.align	3
-	.type	__switch_data, %object
-__switch_data:
-	.quad	__mmap_switched
-	.quad	__bss_start			// x6
-	.quad	__bss_stop			// x7
-	.quad	processor_id			// x4
-	.quad	__fdt_pointer			// x5
-	.quad	memstart_addr			// x6
-	.quad	init_thread_union + THREAD_START_SP // sp
-
 /*
- * The following fragment of code is executed with the MMU on in MMU mode, and
- * uses absolute addresses; this is not position independent.
+ * The following fragment of code is executed with the MMU enabled.
  */
 __mmap_switched:
-	adr	x3, __switch_data + 8
+	adrp	x6, __bss_start
+	adrp	x7, __bss_stop
+	add	x6, x6, :lo12:__bss_start
+	add	x7, x7, :lo12:__bss_stop
 
-	ldp	x6, x7, [x3], #16
 1:	cmp	x6, x7
 	b.hs	2f
 	str	xzr, [x6], #8			// Clear BSS
 	b	1b
 2:
-	ldp	x4, x5, [x3], #16
-	ldr	x6, [x3], #8
-	ldr	x16, [x3]
+	ldr	x16, =(init_thread_union + THREAD_START_SP)
 	mov	sp, x16
-	str	x22, [x4]			// Save processor ID
-	str	x21, [x5]			// Save FDT pointer
-	str	x24, [x6]			// Save PHYS_OFFSET
+	adrp	x4, processor_id
+	adrp	x5, __fdt_pointer
+	adrp	x6, memstart_addr
+	str	x22, [x4, :lo12:processor_id]	// Save processor ID
+	str	x21, [x5, :lo12:__fdt_pointer]	// Save FDT pointer
+	str	x24, [x6, :lo12:memstart_addr]	// Save PHYS_OFFSET
 	mov	x29, #0
 	b	start_kernel
 ENDPROC(__mmap_switched)
-- 
1.8.3.2

[PATCH] arm64: remove __switch_data object from head.S

[Mark Rutland]

Hi Ard,

> +	str	x22, [x4, :lo12:processor_id]	// Save processor ID

We should just get rid of processor_id. It doesn't make sense given
big.LITTLE, we have the information stored per-cpu in cpu_data, and as
far as I can tell nothing relies on it currently.

Thanks,
Mark.