[qemu-s390x] [PULL 02/46] pc-bios/s390-ccw: zero out bss section

[Cornelia Huck]

From: Christian Borntraeger <address@hidden>

The QEMU ELF loader does not zero the bss segment.
This resulted in several bugs, e.g. see

commit 5d739a4787a5 (s390-ccw.img: Fix sporadic errors with ccw boot image - 
initialize css)
commit 6a40fa2669d3 (s390-ccw.img: Initialize next_idx)
commit 8775d91a0f42 (pc-bios/s390-ccw: Fix problem with invalid virtio-scsi LUN 
when rebooting)

Let's fix this once and forever by letting the BIOS zero the bss itself.

Suggested-by: Alexander Graf <address@hidden>
Signed-off-by: Christian Borntraeger <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Thomas Huth <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
Signed-off-by: Cornelia Huck <address@hidden>
---
 pc-bios/s390-ccw/start.S | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
index 43f9bd243e..eb8d024dbb 100644
--- a/pc-bios/s390-ccw/start.S
+++ b/pc-bios/s390-ccw/start.S
@@ -3,7 +3,7 @@
  * into the pc-bios directory of qemu.
  *
  * Copyright (c) 2013 Alexander Graf <address@hidden>
- * Copyright 2013 IBM Corp.
+ * Copyright IBM Corp. 2013, 2017
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or (at
  * your option) any later version. See the COPYING file in the top-level
@@ -13,8 +13,32 @@
         .globl _start
 _start:
 
-larl   %r15, stack + 0x8000    /* Set up stack */
-j      main                    /* And call C */
+       larl   %r15, stack + 0x8000     /* Set up stack */
+
+       /* clear bss */
+       larl %r2, __bss_start
+       larl %r3, _end
+       slgr %r3, %r2           /* get sizeof bss */
+       ltgr    %r3,%r3         /* bss emtpy? */
+       jz      done
+       aghi    %r3,-1
+       srlg    %r4,%r3,8       /* how many 256 byte chunks? */
+       ltgr    %r4,%r4
+       lgr     %r1,%r2
+       jz      remainder
+loop:
+       xc      0(256,%r1),0(%r1)
+       la      %r1,256(%r1)
+       brctg   %r4,loop
+remainder:
+       larl    %r2,memsetxc
+       ex      %r3,0(%r2)
+done:
+       j      main             /* And call C */
+
+memsetxc:
+       xc      0(1,%r1),0(%r1)
+
 
 /*
  * void disabled_wait(void)
-- 
2.13.6