powerpc/64: avoid using r13 in relocate

relocate() uses r13 in early boot before it is used for the paca. Use
a different register for this so r13 is kept unchanged until it is
set to the paca pointer.

Avoid r14 as well while we're here, there's no reason not to use the
volatile registers which is a bit less surprising, and r14 could be used
as another fixed reg one day.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926055620.2676869-4-npiggin@gmail.com

arch/powerpc/kernel/reloc_64.S

@@ -27,8 +27,8 @@ _GLOBAL(relocate)
 	add	r9,r9,r12	/* r9 has runtime addr of .rela.dyn section */
 	ld	r10,(p_st - 0b)(r12)
 	add	r10,r10,r12	/* r10 has runtime addr of _stext */
-	ld	r13,(p_sym - 0b)(r12)
-	add	r13,r13,r12	/* r13 has runtime addr of .dynsym */
+	ld	r4,(p_sym - 0b)(r12)
+	add	r4,r4,r12	/* r4 has runtime addr of .dynsym */
 
 	/*
 	 * Scan the dynamic section for the RELA, RELASZ and RELAENT entries.
@@ -84,16 +84,16 @@ _GLOBAL(relocate)
 	ld	r0,16(r9)	/* reloc->r_addend */
 	b	.Lstore
 .Luaddr64:
-	srdi	r14,r0,32	/* ELF64_R_SYM(reloc->r_info) */
+	srdi	r5,r0,32	/* ELF64_R_SYM(reloc->r_info) */
 	clrldi	r0,r0,32
 	cmpdi	r0,R_PPC64_UADDR64
 	bne	.Lnext
 	ld	r6,0(r9)
 	ld	r0,16(r9)
-	mulli	r14,r14,24	/* 24 == sizeof(elf64_sym) */
-	add	r14,r14,r13	/* elf64_sym[ELF64_R_SYM] */
-	ld	r14,8(r14)
-	add	r0,r0,r14
+	mulli	r5,r5,24	/* 24 == sizeof(elf64_sym) */
+	add	r5,r5,r4	/* elf64_sym[ELF64_R_SYM] */
+	ld	r5,8(r5)
+	add	r0,r0,r5
 .Lstore:
 	add	r0,r0,r3
 	stdx	r0,r7,r6