svn commit: r292194 - head/sys/arm64/arm64

[Andrew Turner]

Author: andrew
Date: Mon Dec 14 10:06:01 2015
New Revision: 292194
URL: https://svnweb.freebsd.org/changeset/base/292194

Log:
  Skip restoring more registers when returning from an exception taken in
  the kernel. These registers are all callee saved, and as such will be
  restored before returning to the exception handler.
  
  Userland still needs these registers to be restored as they may be changed
  by the kernel and we don't currently track these places.

Modified:
  head/sys/arm64/arm64/exception.S

Modified: head/sys/arm64/arm64/exception.S
==============================================================================
--- head/sys/arm64/arm64/exception.S	Mon Dec 14 10:04:57 2015	(r292193)
+++ head/sys/arm64/arm64/exception.S	Mon Dec 14 10:06:01 2015	(r292194)
@@ -90,15 +90,19 @@ __FBSDID("$FreeBSD$");
 	ldp	x14, x15, [sp, #(TF_X + 14 * 8)]
 	ldp	x16, x17, [sp, #(TF_X + 16 * 8)]
 .if \el == 0
+	/*
+	 * We only restore the callee saved registers when returning to
+	 * userland as they may have been updated by a system call or signal.
+	 */
 	ldp	x18, x19, [sp, #(TF_X + 18 * 8)]
-.else
-	ldr	     x19, [sp, #(TF_X + 19 * 8)]
-.endif
 	ldp	x20, x21, [sp, #(TF_X + 20 * 8)]
 	ldp	x22, x23, [sp, #(TF_X + 22 * 8)]
 	ldp	x24, x25, [sp, #(TF_X + 24 * 8)]
 	ldp	x26, x27, [sp, #(TF_X + 26 * 8)]
 	ldp	x28, x29, [sp, #(TF_X + 28 * 8)]
+.else
+	ldr	     x29, [sp, #(TF_X + 29 * 8)]
+.endif
 .if \el == 0
 	add	sp, sp, #(TF_SIZE + 16)
 .else