hmp: Add 'one-insn-per-tb' command equivalent to 'singlestep'

The 'singlestep' HMP command is confusing, because it doesn't
actually have anything to do with single-stepping the CPU.  What it
does do is force TCG emulation to put one guest instruction in each
TB, which can be useful in some situations.

Create a new HMP command  'one-insn-per-tb', so we can document that
'singlestep' is just a deprecated synonym for it, and eventually
perhaps drop it.

We aren't obliged to do deprecate-and-drop for HMP commands,
but it's easy enough to do so, so we do.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230417164041.684562-9-peter.maydell@linaro.org

docs/about/deprecated.rst

@@ -199,6 +199,15 @@ accepted incorrect commands will return an error. Users should make sure that
 all arguments passed to ``device_add`` are consistent with the documented
 property types.
 
+Human Monitor Protocol (HMP) commands
+-------------------------------------
+
+``singlestep`` (since 8.1)
+''''''''''''''''''''''''''
+
+The ``singlestep`` command has been replaced by the ``one-insn-per-tb``
+command, which has the same behaviour but a less misleading name.
+
 Host Architectures
 ------------------
 

hmp-commands.hx

@@ -378,18 +378,35 @@ SRST
   only *tag* as parameter.
 ERST
 
+    {
+        .name       = "one-insn-per-tb",
+        .args_type  = "option:s?",
+        .params     = "[on|off]",
+        .help       = "run emulation with one guest instruction per translation block",
+        .cmd        = hmp_one_insn_per_tb,
+    },
+
+SRST
+``one-insn-per-tb [off]``
+  Run the emulation with one guest instruction per translation block.
+  This slows down emulation a lot, but can be useful in some situations,
+  such as when trying to analyse the logs produced by the ``-d`` option.
+  This only has an effect when using TCG, not with KVM or other accelerators.
+
+  If called with option off, the emulation returns to normal mode.
+ERST
+
     {
         .name       = "singlestep",
         .args_type  = "option:s?",
         .params     = "[on|off]",
-        .help       = "run emulation in singlestep mode or switch to normal mode",
+        .help       = "deprecated synonym for one-insn-per-tb",
-        .cmd        = hmp_singlestep,
+        .cmd        = hmp_one_insn_per_tb,
     },
 
 SRST
 ``singlestep [off]``
-  Run the emulation in single step mode.
+  This is a deprecated synonym for the one-insn-per-tb command.
-  If called with option off, the emulation returns to normal mode.
 ERST
 
     {

include/monitor/hmp.h

@@ -158,7 +158,7 @@ void hmp_info_vcpu_dirty_limit(Monitor *mon, const QDict *qdict);
 void hmp_human_readable_text_helper(Monitor *mon,
                                     HumanReadableText *(*qmp_handler)(Error **));
 void hmp_info_stats(Monitor *mon, const QDict *qdict);
-void hmp_singlestep(Monitor *mon, const QDict *qdict);
+void hmp_one_insn_per_tb(Monitor *mon, const QDict *qdict);
 void hmp_watchdog_action(Monitor *mon, const QDict *qdict);
 void hmp_pcie_aer_inject_error(Monitor *mon, const QDict *qdict);
 void hmp_info_capture(Monitor *mon, const QDict *qdict);

softmmu/runstate-hmp-cmds.c

@@ -40,7 +40,7 @@ void hmp_info_status(Monitor *mon, const QDict *qdict)
     qapi_free_StatusInfo(info);
 }
 
-void hmp_singlestep(Monitor *mon, const QDict *qdict)
+void hmp_one_insn_per_tb(Monitor *mon, const QDict *qdict)
 {
     const char *option = qdict_get_try_str(qdict, "option");
     AccelState *accel = current_accel();

tests/qtest/test-hmp.c

@@ -56,6 +56,7 @@ static const char *hmp_cmds[] = {
     "o /w 0 0x1234",
     "object_add memory-backend-ram,id=mem1,size=256M",
     "object_del mem1",
+    "one-insn-per-tb on",
     "pmemsave 0 4096 \"/dev/null\"",
     "p $pc + 8",
     "qom-list /",