[PATCH] target/ppc: Expose the TB offset of the guest in QEMU monitor

[Gautam Menghani]

When debugging issues in KVM guests, it is sometimes helpful to have a
unified trace log of both guest and host to see where things are going
wrong. Expose the TB (timebase) offset through QEMU monitor to enable
capturing of unified log.

The below steps can be then used to get a unified log:
1. In host
trace-cmd record -e kvm_hv:kvm_guest_enter -e kvm_hv:kvm_guest_exit \
    -C ppc-tb -o trace_host.dat

2. In guest
trace-cmd record -e powerpc:hcall_entry -e powerpc:hcall_exit -C ppc-tb \
    --ts-offset <TB offset from QEMU monitor> -o trace_guest.dat

3. Transfer the guest logs to the host with scp/rsync

4. Unify the logs
trace-cmd report -i trace_host.dat -i trace_guest.dat > combined_log

Signed-off-by: Gautam Menghani <gau...@linux.ibm.com>
---
 hw/ppc/ppc.c          | 5 +++++
 target/ppc/cpu.h      | 1 +
 target/ppc/cpu_init.c | 4 +++-
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index a512d4fa64..1e8eb0ceef 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -515,6 +515,11 @@ uint64_t cpu_ppc_get_tb(ppc_tb_t *tb_env, uint64_t vmclk, 
int64_t tb_offset)
     return ns_to_tb(tb_env->tb_freq, vmclk) + tb_offset;
 }
 
+int64_t cpu_ppc_load_tb_offset(CPUPPCState *env)
+{
+    return llabs(*(&env->tb_env->tb_offset));
+}
+
 uint64_t cpu_ppc_load_tbl (CPUPPCState *env)
 {
     ppc_tb_t *tb_env = env->tb_env;
diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index 057c54bbb8..cbd5964b1a 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -1693,6 +1693,7 @@ void cpu_ppc_store_hdecr(CPUPPCState *env, target_ulong 
value);
 void cpu_ppc_store_tbu40(CPUPPCState *env, uint64_t value);
 uint64_t cpu_ppc_load_purr(CPUPPCState *env);
 void cpu_ppc_store_purr(CPUPPCState *env, uint64_t value);
+int64_t cpu_ppc_load_tb_offset(CPUPPCState *env);
 #if !defined(CONFIG_USER_ONLY)
 target_ulong load_40x_pit(CPUPPCState *env);
 void store_40x_pit(CPUPPCState *env, target_ulong val);
diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c
index a02187ce5a..a77adc3e62 100644
--- a/target/ppc/cpu_init.c
+++ b/target/ppc/cpu_init.c
@@ -7620,8 +7620,10 @@ void ppc_cpu_dump_state(CPUState *cs, FILE *f, int flags)
 #if !defined(CONFIG_USER_ONLY)
     if (env->tb_env) {
         qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64
+                     " TB_OFFSET %016" PRId64
                      " DECR " TARGET_FMT_lu "\n", cpu_ppc_load_tbu(env),
-                     cpu_ppc_load_tbl(env), cpu_ppc_load_decr(env));
+                     cpu_ppc_load_tbl(env), cpu_ppc_load_tb_offset(env),
+                     cpu_ppc_load_decr(env));
     }
 #else
     qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64 "\n", cpu_ppc_load_tbu(env),
-- 
2.54.0