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

Message ID 20171214171004.25058-3-cohuck@redhat.com
State New
Headers show
Series [PULL,01/46] s390x/migration: use zero flag parameter | expand

Commit Message

Cornelia Huck Dec. 14, 2017, 5:09 p.m. UTC 
From: Christian Borntraeger <borntraeger@de.ibm.com>

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 <agraf@suse.de>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20171122142627.73170-3-borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
 pc-bios/s390-ccw/start.S | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)
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Patch

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 <agraf@suse.de>
- * 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)