bsd-user: Add '-one-insn-per-tb' option equivalent to '-singlestep'

The '-singlestep' option 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 command line argument -one-insn-per-tb, so we can
document that -singlestep is just a deprecated synonym for it,
and eventually perhaps drop it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230417164041.684562-6-peter.maydell@linaro.org

bsd-user/main.c

@@ -162,7 +162,8 @@ static void usage(void)
            "-d item1[,...]    enable logging of specified items\n"
            "                  (use '-d help' for a list of log items)\n"
            "-D logfile        write logs to 'logfile' (default stderr)\n"
-           "-singlestep       always run in singlestep mode\n"
+           "-one-insn-per-tb  run with one guest instruction per emulated TB\n"
+           "-singlestep       deprecated synonym for -one-insn-per-tb\n"
            "-strace           log system calls\n"
            "-trace            [[enable=]<pattern>][,events=<file>][,file=<file>]\n"
            "                  specify tracing options\n"
@@ -385,7 +386,7 @@ int main(int argc, char **argv)
             (void) envlist_unsetenv(envlist, "LD_PRELOAD");
         } else if (!strcmp(r, "seed")) {
             seed_optarg = optarg;
-        } else if (!strcmp(r, "singlestep")) {
+        } else if (!strcmp(r, "singlestep") || !strcmp(r, "one-insn-per-tb")) {
             opt_one_insn_per_tb = true;
         } else if (!strcmp(r, "strace")) {
             do_strace = 1;

docs/user/main.rst

@@ -247,5 +247,10 @@ Debug options:
 ``-p pagesize``
    Act as if the host page size was 'pagesize' bytes
 
+``-one-insn-per-tb``
+   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.
+
 ``-singlestep``
-   Run the emulation in single step mode.
+   This is a deprecated synonym for the ``-one-insn-per-tb`` option.