[patch] Arm debug builds

[Paul Brook]

When building a debug build of ld.so on Arm I'm getting assembly errors 
because of out of range offsets in elf_machine_load_address.

The patch below fixes this by using a constant pool instead of and adr 
instruction in unoptimized builds. Contrary to what the old comment says I'm 
fairly sure this implementation is also safe in Thumb mode, so we can use it 
there as well.

Paul

Index: ldso/ldso/arm/dl-sysdep.h
===================================================================
--- ldso/ldso/arm/dl-sysdep.h	(revision 15784)
+++ ldso/ldso/arm/dl-sysdep.h	(working copy)
@@ -86,24 +86,20 @@ elf_machine_load_address (void)
 	extern void __dl_start asm ("_dl_start");
 	Elf32_Addr got_addr = (Elf32_Addr) &__dl_start;
 	Elf32_Addr pcrel_addr;
-#if !defined __thumb__
+#if defined __OPTIMIZE__ && !defined __thumb__
 	asm ("adr %0, _dl_start" : "=r" (pcrel_addr));
 #else
+	/* A simple adr does not work in Thumb mode because the offset is
+	   negative, and for debug builds may be too large.  */
 	int tmp;
-	/* The above adr will not work on thumb because it
-	 * is negative.  The only safe way is to temporarily
-	 * swap to arm.
-	 */
-	asm(   ".align	2\n"
-	"	bx	pc\n"
-	"	nop	\n"
-	"	.arm	\n"
-	"	adr	%0, _dl_start\n"
-	"	.align	2\n"
-	"	orr	%1, pc, #1\n"
-	"	bx	%1\n"
-	"	.force_thumb\n"
-	: "=r" (pcrel_addr), "=&r" (tmp));
+	asm ("adr %1, 1f\n\t"
+		 "ldr %0, [%1]\n\t"
+		 "add %0, %0, %1\n\t"
+		 "b 2f\n\t"
+		 ".align 2\n\t"
+		 "1: .word _dl_start - 1b\n\t"
+		 "2:"
+		 : "=r" (pcrel_addr), "=r" (tmp));
 #endif
 	return pcrel_addr - got_addr;
 }