runtime_exceptions: Save x4-x29 unconditionally

In preparation for SMCCC v1.1 support, save x4 to x29 unconditionally.
Previously we expected callers coming from AArch64 mode to preserve
x8-x17.  This is no longer the case with SMCCC v1.1 as AArch64 callers
only need to save x0-x3.

Change-Id: Ie62d620776533969ff4a02c635422f1b9208be9c
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>

bl31/aarch64/runtime_exceptions.S

 /*
- * Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -153,7 +153,14 @@ interrupt_exit_\label:
 	.endm
 
 
-	.macro save_x18_to_x29_sp_el0
+	.macro save_x4_to_x29_sp_el0
+	stp	x4, x5, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X4]
+	stp	x6, x7, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X6]
+	stp	x8, x9, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X8]
+	stp	x10, x11, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X10]
+	stp	x12, x13, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X12]
+	stp	x14, x15, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X14]
+	stp	x16, x17, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X16]
 	stp	x18, x19, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X18]
 	stp	x20, x21, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X20]
 	stp	x22, x23, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X22]
@@ -297,34 +304,16 @@ smc_handler32:
 	/* Check whether aarch32 issued an SMC64 */
 	tbnz	x0, #FUNCID_CC_SHIFT, smc_prohibited
 
-	/*
-	 * Since we're are coming from aarch32, x8-x18 need to be saved as per
-	 * SMC32 calling convention. If a lower EL in aarch64 is making an
-	 * SMC32 call then it must have saved x8-x17 already therein.
-	 */
-	stp	x8, x9, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X8]
-	stp	x10, x11, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X10]
-	stp	x12, x13, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X12]
-	stp	x14, x15, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X14]
-	stp	x16, x17, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X16]
-
-	/* x4-x7, x18, sp_el0 are saved below */
-
 smc_handler64:
 	/*
 	 * Populate the parameters for the SMC handler.
 	 * We already have x0-x4 in place. x5 will point to a cookie (not used
 	 * now). x6 will point to the context structure (SP_EL3) and x7 will
-	 * contain flags we need to pass to the handler Hence save x5-x7.
+	 * contain flags we need to pass to the handler.
 	 *
-	 * Note: x4 only needs to be preserved for AArch32 callers but we do it
-	 *       for AArch64 callers as well for convenience
+	 * Save x4-x29 and sp_el0.  Refer to SMCCC v1.1.
 	 */
-	stp	x4, x5, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X4]
-	stp	x6, x7, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X6]
-
-	/* Save rest of the gpregs and sp_el0*/
-	save_x18_to_x29_sp_el0
+	save_x4_to_x29_sp_el0
 
 	mov	x5, xzr
 	mov	x6, sp