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

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 for KVM guests 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

  NOTE: The TB offset would be reported as a negative number in QEMU
  monitor. For this step, the minus sign must be ignored.

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

In case of TCG guests, the TB offset would be
reported as 0 since the offset logic is not applicable in this case.

Tested-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
Tested-by: Sneh Shikha Yadav <syadav@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260629052602.78276-1-gautam@linux.ibm.com
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>

diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index a512d4fa647875262e7e3d135b6a8abae5798a11..b123b4cc1cce7852c7821cf3d3bced347ef998ab 100644 (file)
--- 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 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 057c54bbb814bc12581fc6c9255570c842f35604..cbd5964b1acdae315d3766f1e065bbc3524b635f 100644 (file)
--- 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 a02187ce5afbd58f02eaca07662776501a4f5016..8cab5e12b6e6b91e8600b70db5ffb665e3cc5e6c 100644 (file)
--- a/target/ppc/cpu_init.c
+++ b/target/ppc/cpu_init.c
@@ -7620,8 +7620,9 @@ 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
-                     " DECR " TARGET_FMT_lu "\n", cpu_ppc_load_tbu(env),
-                     cpu_ppc_load_tbl(env), cpu_ppc_load_decr(env));
+                     " DECR " TARGET_FMT_lu " TB_OFFSET %016" PRId64 "\n",
+                     cpu_ppc_load_tbu(env), cpu_ppc_load_tbl(env),
+                     cpu_ppc_load_decr(env), cpu_ppc_load_tb_offset(env));
     }
 #else
     qemu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64 "\n", cpu_ppc_load_tbu(env),