Various version of gcc, when compiling with -Og, complain:

  xg_sr_common_x86.c: In function 'write_x86_cpu_policy_records':
  xg_sr_common_x86.c:92:12: error: 'rc' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     92 |     return rc;
        |            ^~

The complaint is legitimate, and can occur with unexpected behaviour of two
related hypercalls in combination with a libc which permits zero-length
malloc()s.

Have an explicit rc = 0 on the success path, and make the MSRs record error
handling consistent with the CPUID record before it.

Fixes: f6b2b8ec53d ("libxc/save: Write X86_{CPUID,MSR}_DATA records")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Ian Jackson <iwj@xenproject.org>
CC: Wei Liu <wl@xen.org>
---
 tools/libs/guest/xg_sr_common_x86.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/libs/guest/xg_sr_common_x86.c b/tools/libs/guest/xg_sr_common_x86.c
index 6f12483907..3168c5485f 100644
--- a/tools/libs/guest/xg_sr_common_x86.c
+++ b/tools/libs/guest/xg_sr_common_x86.c
@@ -83,7 +83,13 @@ int write_x86_cpu_policy_records(struct xc_sr_context *ctx)
 
     msrs.length = nr_msrs * sizeof(xen_msr_entry_t);
     if ( msrs.length )
+    {
         rc = write_record(ctx, &msrs);
+        if ( rc )
+            goto out;
+    }
+
+    rc = 0;
 
  out:
     free(cpuid.data);
-- 
2.11.0

Andrew Cooper writes ("[PATCH 02/10] tools/libxg: Fix uninitialised variable in write_x86_cpu_policy_records()"):
> Fixes: f6b2b8ec53d ("libxc/save: Write X86_{CPUID,MSR}_DATA records")
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Release-Acked-by: Ian Jackson <iwj@xenproject.org>

On 12.02.2021 16:39, Andrew Cooper wrote:
> Various version of gcc, when compiling with -Og, complain:
> 
>   xg_sr_common_x86.c: In function 'write_x86_cpu_policy_records':
>   xg_sr_common_x86.c:92:12: error: 'rc' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>      92 |     return rc;
>         |            ^~
> 
> The complaint is legitimate, and can occur with unexpected behaviour of two
> related hypercalls in combination with a libc which permits zero-length
> malloc()s.
> 
> Have an explicit rc = 0 on the success path, and make the MSRs record error
> handling consistent with the CPUID record before it.
> 
> Fixes: f6b2b8ec53d ("libxc/save: Write X86_{CPUID,MSR}_DATA records")
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>