x86: fix a crash when adding both legacy AMD and CPUID 0x04 caches

The old code increased numcaches in the second case
but it added additional caches at the beginning of the array.
Uninitialized caches in the array caused a divide by zero
(cache->nbthreads_sharing) when used later.

Only occurs if the CPUID vendor isn't recognized
(neither Intel, nor AMD, nor Zhaoxin) or in case
of clang 4.0 bug on FreeBSD11.1 (#282).

That's also why the code was crashing on Zhaoxin
instead of just reporting wrong topology (#279).

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
(cherry picked from commit a6f013c)

NEWS

@@ -22,6 +22,7 @@ Version 1.11.9
 * Add support for Zhaoxin ZX-C and ZX-D processors in the x86 backend,
   thanks to Jeff Zhao for the patch.
 * Fix AMD Epyc 24-core L3 cache locality in the x86 backend.
+* Don't crash in the x86 backend when the CPUID vendor string is unknown.
 * Fix the missing pu discovery support bit on some OS.
 * Fix the management of the lstopoStyle info attribute for custom colors.
 * Add verbose warnings when failing to load hwloc v2.0+ XMLs.

src/topology-x86.c

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2010-2017 Inria.  All rights reserved.
+ * Copyright © 2010-2018 Inria.  All rights reserved.
  * Copyright © 2010-2013 Université Bordeaux
  * Copyright © 2010-2011 Cisco Systems, Inc.  All rights reserved.
  * See COPYING in top-level directory.
@@ -250,6 +250,9 @@ static void look_proc(struct hwloc_backend *backend, struct procinfo *infos, uns
   if (cpuid_type != intel && cpuid_type != zhaoxin && has_topoext(features)) {
     unsigned apic_id, node_id, nodes_per_proc;
 
+    /* the code below doesn't want any other cache yet */
+    assert(!infos->numcaches);
+
     eax = 0x8000001e;
     hwloc_x86_cpuid(&eax, &ebx, &ecx, &edx);
     infos->apicid = apic_id = eax;
@@ -357,6 +360,9 @@ static void look_proc(struct hwloc_backend *backend, struct procinfo *infos, uns
    */
   if (cpuid_type != amd && highest_cpuid >= 0x04) {
     unsigned level;
+
+    unsigned oldnumcaches = infos->numcaches; /* in case we got caches above */
+
     for (cachenum = 0; ; cachenum++) {
       unsigned type;
       eax = 0x04;
@@ -386,7 +392,8 @@ static void look_proc(struct hwloc_backend *backend, struct procinfo *infos, uns
       }
     }
 
-    cache = infos->cache = malloc(infos->numcaches * sizeof(*infos->cache));
+    infos->cache = realloc(infos->cache, infos->numcaches * sizeof(*infos->cache));
+    cache = &infos->cache[oldnumcaches];
 
     for (cachenum = 0; ; cachenum++) {
       unsigned long linesize, linepart, ways, sets;