MIPS: Call relocate_kernel if CONFIG_RELOCATABLE=y

If CONFIG_RELOCATABLE is enabled, call relocate_kernel.

This function will return the entry point of the relocated kernel if
copy/relocate is sucessful or the original entry point if not. The stack
pointer must then be pointed into the new image.
Signed-off-by: NMatt Redfearn <matt.redfearn@imgtec.com>
Cc: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: kernel-hardening@lists.openwall.com
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12984/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/head.S

@@ -132,7 +132,27 @@ not_found:
 	set_saved_sp	sp, t0, t1
 	PTR_SUBU	sp, 4 * SZREG		# init stack pointer
 
+#ifdef CONFIG_RELOCATABLE
+	/* Copy kernel and apply the relocations */
+	jal		relocate_kernel
+
+	/* Repoint the sp into the new kernel image */
+	PTR_LI		sp, _THREAD_SIZE - 32 - PT_SIZE
+	PTR_ADDU	sp, $28
+	set_saved_sp	sp, t0, t1
+	PTR_SUBU	sp, 4 * SZREG		# init stack pointer
+
+	/*
+	 * relocate_kernel returns the entry point either
+	 * in the relocated kernel or the original if for
+	 * some reason relocation failed - jump there now
+	 * with instruction hazard barrier because of the
+	 * newly sync'd icache.
+	 */
+	jr.hb		v0
+#else
 	j		start_kernel
+#endif
 	END(kernel_entry)
 
 #ifdef CONFIG_SMP