From 609d8661171760c7ead04f64359d47a77c31d474 Mon Sep 17 00:00:00 2001
From: Thomas Huth <thuth@redhat.com>
Date: Fri, 23 Apr 2021 10:30:51 +0200
Subject: [PATCH 29/39] pc-bios/s390-ccw: Use reset_psw pointer instead of
 hard-coded null pointer
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RH-Author: Jon Maloy <jmaloy@redhat.com>
RH-MergeRequest: 24: v7:  Add support for building qemu-kvm with clang and safe-stack
RH-Commit: [2/11] c65a986104a1830847e772879ca6eaf76c86b2f3 (jmaloy/qemu-kvm-centos-jon)
RH-Bugzilla: 1939509 1940132
RH-Acked-by: Danilo Cesar Lemes de Paula <ddepaula@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>

When compiling the s390-ccw bios with clang, it emits a warning like this:

 pc-bios/s390-ccw/jump2ipl.c:86:9: warning: indirection of non-volatile null
  pointer will be deleted, not trap [-Wnull-dereference]
     if (*((uint64_t *)0) & RESET_PSW_MASK) {
         ^~~~~~~~~~~~~~~~
 pc-bios/s390-ccw/jump2ipl.c:86:9: note: consider using __builtin_trap() or
  qualifying pointer with 'volatile'

We could add a "volatile" here to shut it up, but on the other hand,
we also have a pointer variable called "reset_psw" in this file already
that points to the PSW at address 0, so we can simply use that pointer
variable instead.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210423142440.582188-1-thuth@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit ff77712a8a2e15e5901fad35b9a6bb65974b2e4a)
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 pc-bios/s390-ccw/jump2ipl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
index b9c70d64a5..73e4367e09 100644
--- a/pc-bios/s390-ccw/jump2ipl.c
+++ b/pc-bios/s390-ccw/jump2ipl.c
@@ -82,8 +82,8 @@ void jump_to_low_kernel(void)
         jump_to_IPL_code(KERN_IMAGE_START);
     }
 
-    /* Trying to get PSW at zero address */
-    if (*((uint64_t *)0) & RESET_PSW_MASK) {
+    /* Trying to get PSW at zero address (pointed to by reset_psw) */
+    if (*reset_psw & RESET_PSW_MASK) {
         /*
          * Surely nobody will try running directly from lowcore, so
          * let's use 0 as an indication that we want to load the reset
-- 
2.27.0