[RFC PATCH] target/ppc: don't print TB in ppc_cpu_dump_state if it's not initialized

[Matheus Ferst]

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>
---
This patch fixes the reported problem, but may be an incomplete solution
since many other places dereference env->tb_env without checking for
NULL. AFAICS, "-machine none" is the only way to trigger this problem,
and I'm not familiar with the use-cases for this option.

Should we stop assuming env->tb_env != NULL and add checks everywhere?
Or should we find a way to provide Time Base/Decrementer for
"-machine none"?
---
 target/ppc/cpu_init.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c
index 86ad28466a..7e96baac9f 100644
--- a/target/ppc/cpu_init.c
+++ b/target/ppc/cpu_init.c
@@ -7476,18 +7476,18 @@ 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 (env->tb_env) {
+        qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64
 #if !defined(CONFIG_USER_ONLY)
-                 " DECR " TARGET_FMT_lu
+                     " DECR " TARGET_FMT_lu
 #endif
-                 "\n",
-                 cpu_ppc_load_tbu(env), cpu_ppc_load_tbl(env)
+                     "\n",
+                     cpu_ppc_load_tbu(env), cpu_ppc_load_tbl(env)
 #if !defined(CONFIG_USER_ONLY)
-                 , cpu_ppc_load_decr(env)
-#endif
-        );
+                     , cpu_ppc_load_decr(env)
 #endif
+            );
+    }
     for (i = 0; i < 32; i++) {
         if ((i & (RGPL - 1)) == 0) {
             qemu_fprintf(f, "GPR%02d", i);
-- 
2.25.1