[PATCH] libxc: remove / adjust xc_get_cpufreq_para()'s BUILD_BUG_ON()s

[Jan Beulich <jbeulich@xxxxxxxx>]

The full structures cannot match in layout, as soon as a 32-bit tool
stack build comes into play. But it also doesn't need to; the part of
the layouts that needs to match is merely the union that we memcpy()
from the sysctl structure to the xc one. Keep (in adjusted form) only
the relevant ones.

Since the whole block needs touching anyway, move it closer to the
respective memcpy() and use a wrapper macro to limit verbosity.

Fixes: 2381dfab083f ("xen/sysctl: Nest cpufreq scaling options")
Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/libs/ctrl/xc_pm.c
+++ b/tools/libs/ctrl/xc_pm.c
@@ -248,45 +248,6 @@ int xc_get_cpufreq_para(xc_interface *xc
     sys_para->freq_num = user_para->freq_num;
     sys_para->gov_num  = user_para->gov_num;
 
-    /* Sanity check struct layout */
-    BUILD_BUG_ON(sizeof(*user_para) != sizeof(*sys_para));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), cpu_num) !=
-                 offsetof(typeof(*sys_para),  cpu_num));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), freq_num) !=
-                 offsetof(typeof(*sys_para),  freq_num));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), gov_num) !=
-                 offsetof(typeof(*sys_para),  gov_num));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), affected_cpus) !=
-                 offsetof(typeof(*sys_para),  affected_cpus));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), scaling_available_frequencies) !=
-                 offsetof(typeof(*sys_para),  scaling_available_frequencies));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), scaling_available_governors) !=
-                 offsetof(typeof(*sys_para),  scaling_available_governors));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), scaling_driver) !=
-                 offsetof(typeof(*sys_para),  scaling_driver));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), cpuinfo_cur_freq) !=
-                 offsetof(typeof(*sys_para),  cpuinfo_cur_freq));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), cpuinfo_max_freq) !=
-                 offsetof(typeof(*sys_para),  cpuinfo_max_freq));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), cpuinfo_min_freq) !=
-                 offsetof(typeof(*sys_para),  cpuinfo_min_freq));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.s.scaling_cur_freq) !=
-                 offsetof(typeof(*sys_para),  u.s.scaling_cur_freq));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.s.scaling_governor) !=
-                 offsetof(typeof(*sys_para),  u.s.scaling_governor));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.s.scaling_max_freq) !=
-                 offsetof(typeof(*sys_para),  u.s.scaling_max_freq));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.s.scaling_min_freq) !=
-                 offsetof(typeof(*sys_para),  u.s.scaling_min_freq));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.s.u.userspace) !=
-                 offsetof(typeof(*sys_para),  u.s.u.userspace));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.s.u.ondemand) !=
-                 offsetof(typeof(*sys_para),  u.s.u.ondemand));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), u.cppc_para) !=
-                 offsetof(typeof(*sys_para),  u.cppc_para));
-    BUILD_BUG_ON(offsetof(typeof(*user_para), turbo_enabled) !=
-                 offsetof(typeof(*sys_para),  turbo_enabled));
-
     ret = xc_sysctl(xch, &sysctl);
     if ( ret )
     {
@@ -316,6 +277,22 @@ int xc_get_cpufreq_para(xc_interface *xc
         BUILD_BUG_ON(sizeof(((struct xc_get_cpufreq_para *)0)->u) !=
                     sizeof(((struct xen_get_cpufreq_para *)0)->u));
 
+        /* Sanity check layout of the union subject to memcpy() below. */
+        BUILD_BUG_ON(sizeof(user_para->u) != sizeof(sys_para->u));
+#define CHK_FIELD(fld) \
+        BUILD_BUG_ON(offsetof(typeof(user_para->u), fld) != \
+                     offsetof(typeof(sys_para->u),  fld))
+
+        CHK_FIELD(s.scaling_cur_freq);
+        CHK_FIELD(s.scaling_governor);
+        CHK_FIELD(s.scaling_max_freq);
+        CHK_FIELD(s.scaling_min_freq);
+        CHK_FIELD(s.u.userspace);
+        CHK_FIELD(s.u.ondemand);
+        CHK_FIELD(cppc_para);
+
+#undef CHK_FIELD
+
         memcpy(&user_para->u, &sys_para->u, sizeof(sys_para->u));
     }