[Qemu-devel] [RFC PATCH] vl.c: add -semihosting-config "arg" sub-argument

[Leon Alrae <leon.alrae@imgtec.com>]

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
---
Hi,

Continuing the discussion related to extending QEMU's command line with new
argument allowing to pass semi-hosting input arguments to the guest program:
https://lists.gnu.org/archive/html/qemu-devel/2015-03/msg05960.html

This simple patch adds "arg" sub-argument which in my opinion is flexible
enough to satisfy semi-hosting interfaces which allocate buffers at runtime
(so it is possible to pass any number of strings of any length) as well as the
ones which have limited buffer for a single input string.

Highlights:

* arg can appear multiple times in -semihosting-config group of sub-arguments
  and is used to create argc/argv.

* Single string cmdline can be still easily created:
    static void concat_semihosting_args(char *buffer, int buffer_size,
                                        const char *separator)
    {
        int i;
        buffer[0] = '\0';
        for (i = 0; i < semihosting_argc - 1; i++) {
            pstrcat(buffer, buffer_size, semihosting_argv[i]);
            pstrcat(buffer, buffer_size, separator);
        }
        pstrcat(buffer, buffer_size, semihosting_argv[i]);
    }

* argv[0] is set by the first occurence of "arg" rather than taking the same
  string from "-kernel". This might be required in cases where the path is too
  long and semi-hosting app's buffer for the cmdline is fixed and small.

* No altering the parser itself, just traversing the -semihosting-config opts
  and picking all arg strings.

* This patch doesn't fix the need of using double-commas if user want to have
  a comma in the string.

If we agree on this new option then I would like to follow up with a clean up
where we've got a semi-hosting specific structure rather than keep generating
more semihosting_* variables (I skipped it in this patch to avoid generating
clean up related noise in the diff).

Any comments?

Thanks,
Leon
---
 include/sysemu/sysemu.h |  2 ++
 vl.c                    | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 8a52934..651863f 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -126,6 +126,8 @@ extern int graphic_rotate;
 extern int no_quit;
 extern int no_shutdown;
 extern int semihosting_enabled;
+extern const char **semihosting_argv;
+extern int semihosting_argc;
 extern int old_param;
 extern int boot_menu;
 extern bool boot_strict;
diff --git a/vl.c b/vl.c
index 74c2681..640d9da 100644
--- a/vl.c
+++ b/vl.c
@@ -171,6 +171,8 @@ const char *watchdog;
 QEMUOptionRom option_rom[MAX_OPTION_ROMS];
 int nb_option_roms;
 int semihosting_enabled = 0;
+const char **semihosting_argv;
+int semihosting_argc;
 int old_param = 0;
 const char *qemu_name;
 int alt_grab = 0;
@@ -485,6 +487,9 @@ static QemuOptsList qemu_semihosting_config_opts = {
         }, {
             .name = "target",
             .type = QEMU_OPT_STRING,
+        }, {
+            .name = "arg",
+            .type = QEMU_OPT_STRING,
         },
         { /* end of list */ }
     },
@@ -2727,6 +2732,17 @@ static void set_memory_options(uint64_t *ram_slots, ram_addr_t *maxram_size)
     }
 }
 
+static int add_semihosting_arg(const char *name, const char *val, void *opaque)
+{
+    if (strcmp(name, "arg") == 0) {
+        semihosting_argc++;
+        semihosting_argv = g_realloc(semihosting_argv,
+                                     semihosting_argc * sizeof(void *));
+        semihosting_argv[semihosting_argc - 1] = val;
+    }
+    return 0;
+}
+
 int main(int argc, char **argv, char **envp)
 {
     int i;
@@ -3562,6 +3578,8 @@ int main(int argc, char **argv, char **envp)
                     } else {
                         semihosting_target = SEMIHOSTING_TARGET_AUTO;
                     }
+                    /* Set semihosting argument count and vector */
+                    qemu_opt_foreach(opts, add_semihosting_arg, NULL, 0);
                 } else {
                     fprintf(stderr, "Unsupported semihosting-config %s\n",
                             optarg);
-- 
2.1.0