arm: fixup the parasite arguments automatically

The ARM parasite head uses a pad of 228 bytes
to make the offset of the symbol __export_parasite_stack
representable in the ARM instruction set. This value
needs to be changed every time the value of the macro
PARASITE_STACK_SIZE changes.

This patch makes this manual interference redundant.
Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

arch/arm/parasite-head.S

@@ -3,20 +3,34 @@
 
 	.section .head.text, "ax"
 ENTRY(__export_parasite_head_start)
-	adr	%sp, __export_parasite_stack
+	sub	%r2, %pc, #8			@ get the address of this instruction
+
+	adr	%sp, parasite_stack_ptr
+	ldr	%sp, [%sp]
+	add	%sp, %sp, %r2			@ fixup __export_parasite_stack
+	bic	%sp, %sp, #7			@ align the stack
+
         adr     %r0, __export_parasite_cmd
 	ldr	%r0, [%r0]
-        adr     %r1, __export_parasite_args
+
+        adr     %r1, parasite_args_ptr
+	ldr	%r1, [%r1]
+	add	%r1, %r1, %r2			@ fixup __export_parasite_args
+
 	bl	parasite_service
         .byte   0xf0, 0x01, 0xf0, 0xe7          @ the instruction UDF #32 generates the signal SIGTRAP in Linux
 
+parasite_args_ptr:
+	.long __export_parasite_args
+
+parasite_stack_ptr:
+	.long __export_parasite_stack
+
 __export_parasite_cmd:
 	.long 0
-__export_parasite_args:
 	.space PARASITE_STACK_SIZE,0
 
-        .space 228, 0
-
+.align 3
 __export_parasite_stack:
 	.long 0
 END(__export_parasite_head_start)