target/ppc: check tb_env != 0 before printing TBU/TBL/DECR

When using "-machine none", env->tb_env is not allocated, causing the
segmentation fault reported in issue #85 (launchpad bug #811683). To
avoid this problem, check if the pointer != NULL before calling the
methods to print TBU/TBL/DECR.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/85
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220714172343.80539-1-matheus.ferst@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

target/ppc/cpu_init.c

@@ -7471,17 +7471,15 @@ void ppc_cpu_dump_state(CPUState *cs, FILE *f, int flags)
                  "%08x iidx %d didx %d\n",
                  env->msr, env->spr[SPR_HID0], env->hflags,
                  cpu_mmu_index(env, true), cpu_mmu_index(env, false));
-#if !defined(NO_TIMER_DUMP)
-    qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64
 #if !defined(CONFIG_USER_ONLY)
-                 " DECR " TARGET_FMT_lu
-#endif
-                 "\n",
-                 cpu_ppc_load_tbu(env), cpu_ppc_load_tbl(env)
-#if !defined(CONFIG_USER_ONLY)
-                 , cpu_ppc_load_decr(env)
-#endif
-        );
+    if (env->tb_env) {
+        qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64
+                     " DECR " TARGET_FMT_lu "\n", cpu_ppc_load_tbu(env),
+                     cpu_ppc_load_tbl(env), cpu_ppc_load_decr(env));
+    }
+#else
+    qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64 "\n", cpu_ppc_load_tbu(env),
+                 cpu_ppc_load_tbl(env));
 #endif
     for (i = 0; i < 32; i++) {
         if ((i & (RGPL - 1)) == 0) {

target/ppc/monitor.c

@@ -55,6 +55,9 @@ static target_long monitor_get_decr(Monitor *mon, const struct MonitorDef *md,
                                     int val)
 {
     CPUArchState *env = mon_get_cpu_env(mon);
+    if (!env->tb_env) {
+        return 0;
+    }
     return cpu_ppc_load_decr(env);
 }
 
@@ -62,6 +65,9 @@ static target_long monitor_get_tbu(Monitor *mon, const struct MonitorDef *md,
                                    int val)
 {
     CPUArchState *env = mon_get_cpu_env(mon);
+    if (!env->tb_env) {
+        return 0;
+    }
     return cpu_ppc_load_tbu(env);
 }
 
@@ -69,6 +75,9 @@ static target_long monitor_get_tbl(Monitor *mon, const struct MonitorDef *md,
                                    int val)
 {
     CPUArchState *env = mon_get_cpu_env(mon);
+    if (!env->tb_env) {
+        return 0;
+    }
     return cpu_ppc_load_tbl(env);
 }