[PATCH] hw/arm/bcm2835_property: Implement "get command line" message

[Daniel Bertalan <dani@danielbertalan.dev>]

This query copies the kernel command line into the message buffer. It
was previously stubbed out to return empty, this commit makes it reflect
the arguments specified with `-append`.

I observed the following peculiarities on my Pi 3B+:
- If the buffer is shorter than the string, the response header gives
  the full length, but no data is actually copied.
- No NUL terminator is added: even if the buffer is long enough to fit
  one, the buffer's original contents are preserved past the string's
  end.
- The VC firmware adds the following extra parameters beside the
  user-supplied ones (via /boot/cmdline.txt): `video`, `vc_mem.mem_base`
  and `vc_mem.mem_size`. This is currently not implemented in qemu.

Signed-off-by: Daniel Bertalan <dani@danielbertalan.dev>
---
 hw/arm/bcm2835_peripherals.c       | 2 ++
 hw/arm/bcm2836.c                   | 2 ++
 hw/arm/raspi.c                     | 2 ++
 hw/misc/bcm2835_property.c         | 7 ++++++-
 include/hw/misc/bcm2835_property.h | 1 +
 5 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/hw/arm/bcm2835_peripherals.c b/hw/arm/bcm2835_peripherals.c
index 3c2a4160cd..0233038b95 100644
--- a/hw/arm/bcm2835_peripherals.c
+++ b/hw/arm/bcm2835_peripherals.c
@@ -90,6 +90,8 @@ static void bcm2835_peripherals_init(Object *obj)
                             TYPE_BCM2835_PROPERTY);
     object_property_add_alias(obj, "board-rev", OBJECT(&s->property),
                               "board-rev");
+    object_property_add_alias(obj, "command-line", OBJECT(&s->property),
+                              "command-line");
 
     object_property_add_const_link(OBJECT(&s->property), "fb",
                                    OBJECT(&s->fb));
diff --git a/hw/arm/bcm2836.c b/hw/arm/bcm2836.c
index f894338fc6..166dc896c0 100644
--- a/hw/arm/bcm2836.c
+++ b/hw/arm/bcm2836.c
@@ -55,6 +55,8 @@ static void bcm2836_init(Object *obj)
                             TYPE_BCM2835_PERIPHERALS);
     object_property_add_alias(obj, "board-rev", OBJECT(&s->peripherals),
                               "board-rev");
+    object_property_add_alias(obj, "command-line", OBJECT(&s->peripherals),
+                              "command-line");
     object_property_add_alias(obj, "vcram-size", OBJECT(&s->peripherals),
                               "vcram-size");
 }
diff --git a/hw/arm/raspi.c b/hw/arm/raspi.c
index 92d068d1f9..7b9221c924 100644
--- a/hw/arm/raspi.c
+++ b/hw/arm/raspi.c
@@ -280,6 +280,8 @@ static void raspi_machine_init(MachineState *machine)
     object_property_add_const_link(OBJECT(&s->soc), "ram", OBJECT(machine->ram));
     object_property_set_int(OBJECT(&s->soc), "board-rev", board_rev,
                             &error_abort);
+    object_property_set_str(OBJECT(&s->soc), "command-line",
+                            machine->kernel_cmdline, &error_abort);
     qdev_realize(DEVICE(&s->soc), NULL, &error_fatal);
 
     /* Create and plug in the SD cards */
diff --git a/hw/misc/bcm2835_property.c b/hw/misc/bcm2835_property.c
index 890ae7bae5..225bce2ba4 100644
--- a/hw/misc/bcm2835_property.c
+++ b/hw/misc/bcm2835_property.c
@@ -282,7 +282,11 @@ static void bcm2835_property_mbox_push(BCM2835PropertyState *s, uint32_t value)
             break;
 
         case 0x00050001: /* Get command line */
-            resplen = 0;
+            resplen = strlen(s->command_line);
+            if (bufsize >= resplen)
+                address_space_write(&s->dma_as, value + 12,
+                                    MEMTXATTRS_UNSPECIFIED, s->command_line,
+                                    resplen);
             break;
 
         default:
@@ -413,6 +417,7 @@ static void bcm2835_property_realize(DeviceState *dev, Error **errp)
 
 static Property bcm2835_property_props[] = {
     DEFINE_PROP_UINT32("board-rev", BCM2835PropertyState, board_rev, 0),
+    DEFINE_PROP_STRING("command-line", BCM2835PropertyState, command_line),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/include/hw/misc/bcm2835_property.h b/include/hw/misc/bcm2835_property.h
index 712b76b7a3..ba8896610c 100644
--- a/include/hw/misc/bcm2835_property.h
+++ b/include/hw/misc/bcm2835_property.h
@@ -30,6 +30,7 @@ struct BCM2835PropertyState {
     MACAddr macaddr;
     uint32_t board_rev;
     uint32_t addr;
+    char *command_line;
     bool pending;
 };
 
-- 
2.40.0