Re: [PATCH v3 2/2] s390x: Use strpadcpy for copying vm name

[Thomas Huth]

On 14/01/2021 08.07, Miroslav Rezanina wrote:

Using strncpy with length equal to the size of target array, GCC 11
reports following warning:

   warning: '__builtin_strncpy' specified bound 256 equals destination size 
[-Wstringop-truncation]

We can prevent this warning by using strpadcpy that copies string
up to specified length, zeroes target array after copied string
and does not raise warning when length is equal to target array
size (and ending '\0' is discarded).

Signed-off-by: Miroslav Rezanina <mreza...@redhat.com>
---
  target/s390x/kvm.c         | 12 +++++-------
  target/s390x/misc_helper.c |  7 +++++--
  2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index b8385e6b95..dc27fa36c9 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -29,6 +29,7 @@
  #include "internal.h"
  #include "kvm_s390x.h"
  #include "sysemu/kvm_int.h"
+#include "qemu/cutils.h"
  #include "qapi/error.h"
  #include "qemu/error-report.h"
  #include "qemu/timer.h"
@@ -1910,18 +1911,15 @@ static void insert_stsi_3_2_2(S390CPU *cpu, __u64 addr, 
uint8_t ar)
                                                      strlen(qemu_name)));
      }
      sysib.vm[0].ext_name_encoding = 2; /* 2 = UTF-8 */
-    memset(sysib.ext_names[0], 0, sizeof(sysib.ext_names[0]));
      /* If hypervisor specifies zero Extended Name in STSI322 SYSIB, it's
       * considered by s390 as not capable of providing any Extended Name.
       * Therefore if no name was specified on qemu invocation, we go with the
       * same "KVMguest" default, which KVM has filled into short name field.
       */
-    if (qemu_name) {
-        strncpy((char *)sysib.ext_names[0], qemu_name,
-                sizeof(sysib.ext_names[0]));
-    } else {
-        strcpy((char *)sysib.ext_names[0], "KVMguest");
-    }
+    strpadcpy((char *)sysib.ext_names[0],
+              sizeof(sysib.ext_names[0]),
+              qemu_name ?: "KVMguest", '\0');
+
      /* Insert UUID */
      memcpy(sysib.vm[0].uuid, &qemu_uuid, sizeof(sysib.vm[0].uuid));

diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c

index 58dbc023eb..7ea90d414a 100644
--- a/target/s390x/misc_helper.c
+++ b/target/s390x/misc_helper.c
@@ -19,6 +19,7 @@
   */

#include "qemu/osdep.h"

+#include "qemu/cutils.h"
  #include "qemu/main-loop.h"
  #include "cpu.h"
  #include "internal.h"
@@ -369,8 +370,10 @@ uint32_t HELPER(stsi)(CPUS390XState *env, uint64_t a0, 
uint64_t r0, uint64_t r1)
                  ebcdic_put(sysib.sysib_322.vm[0].name, qemu_name,
                             MIN(sizeof(sysib.sysib_322.vm[0].name),
                                 strlen(qemu_name)));
-                strncpy((char *)sysib.sysib_322.ext_names[0], qemu_name,
-                        sizeof(sysib.sysib_322.ext_names[0]));
+                strpadcpy((char *)sysib.sysib_322.ext_names[0],
+                          sizeof(sysib.sysib_322.ext_names[0]),
+                          qemu_name, '\0');
+
              } else {
                  ebcdic_put(sysib.sysib_322.vm[0].name, "TCGguest", 8);
                  strcpy((char *)sysib.sysib_322.ext_names[0], "TCGguest");

Reviewed-by: Thomas Huth <th...@redhat.com>