[PATCH for-4.19] xen/arm: static-shmem: fix "gbase/pbase used uninitialized" build failure

[Michal Orzel <michal.orzel@xxxxxxx>]

Building Xen with CONFIG_STATIC_SHM=y results in a build failure:

arch/arm/static-shmem.c: In function 'process_shm':
arch/arm/static-shmem.c:327:41: error: 'gbase' may be used uninitialized 
[-Werror=maybe-uninitialized]
  327 |         if ( is_domain_direct_mapped(d) && (pbase != gbase) )
arch/arm/static-shmem.c:305:17: note: 'gbase' was declared here
  305 |         paddr_t gbase, pbase, psize;

This is because the commit cb1ddafdc573 adds a check referencing
gbase/pbase variables which were not yet assigned a value. Fix it.

Fixes: cb1ddafdc573 ("xen/arm/static-shmem: Static-shmem should be 
direct-mapped for direct-mapped domains")
Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
Rationale for 4.19: this patch fixes a build failure reported by CI:
https://gitlab.com/xen-project/xen/-/jobs/7131807878
---
 xen/arch/arm/static-shmem.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/static-shmem.c b/xen/arch/arm/static-shmem.c
index c434b96e6204..cd48d2896b7e 100644
--- a/xen/arch/arm/static-shmem.c
+++ b/xen/arch/arm/static-shmem.c
@@ -324,12 +324,6 @@ int __init process_shm(struct domain *d, struct 
kernel_info *kinfo,
             printk("%pd: static shared memory bank not found: '%s'", d, 
shm_id);
             return -ENOENT;
         }
-        if ( is_domain_direct_mapped(d) && (pbase != gbase) )
-        {
-            printk("%pd: physical address 0x%"PRIpaddr" and guest address 
0x%"PRIpaddr" are not direct-mapped.\n",
-                   d, pbase, gbase);
-            return -EINVAL;
-        }
 
         pbase = boot_shm_bank->start;
         psize = boot_shm_bank->size;
@@ -353,6 +347,13 @@ int __init process_shm(struct domain *d, struct 
kernel_info *kinfo,
             /* guest phys address is after host phys address */
             gbase = dt_read_paddr(cells + addr_cells, addr_cells);
 
+            if ( is_domain_direct_mapped(d) && (pbase != gbase) )
+            {
+                printk("%pd: physical address 0x%"PRIpaddr" and guest address 
0x%"PRIpaddr" are not direct-mapped.\n",
+                       d, pbase, gbase);
+                return -EINVAL;
+            }
+
             for ( i = 0; i < PFN_DOWN(psize); i++ )
                 if ( !mfn_valid(mfn_add(maddr_to_mfn(pbase), i)) )
                 {
-- 
2.25.1