Toolchain: Patch QEMU to support reading kernel cmdline via RPI Mailbox

This commit backports my upstream QEMU patch to implement this
functionality, which is currently waiting for review.

It was submitted here:
https://lists.nongnu.org/archive/html/qemu-arm/2023-04/msg00549

Toolchain/BuildQemu.sh

@@ -37,13 +37,19 @@ pushd "$DIR/Tarballs"
         exit 1
     fi
 
-    if [ ! -d "$QEMU_VERSION" ]; then
-        echo "Extracting qemu..."
-        tar -xf "${QEMU_ARCHIVE}"
-    else
-        echo "Skipped extracting qemu"
+    # If the source directory exists, re-extract it again in case the patches have changed.
+    if [ -d "qemu-$QEMU_VERSION" ]; then
+        rm -rf "qemu-$QEMU_VERSION"
     fi
 
+    echo "Extracting qemu..."
+    tar -xf "${QEMU_ARCHIVE}"
+
+    pushd "qemu-$QEMU_VERSION"
+        for patch in "${DIR}"/Patches/qemu/*.patch; do
+            patch -p1 < "${patch}" > /dev/null
+        done
+    popd
 popd
 
 mkdir -p "$PREFIX"

Toolchain/Patches/qemu/raspberry-pi-command-line.patch

@@ -0,0 +1,109 @@
+From 8b4eba1d4f41c5e07d2be1de6deb545dee4a2eb1 Mon Sep 17 00:00:00 2001
+From: Daniel Bertalan <dani@danielbertalan.dev>
+Date: Tue, 25 Apr 2023 11:35:52 +0200
+Subject: [PATCH] hw/arm/bcm2835_property: Implement "get command line" message
+
+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(-)
+
+This patch has been submitted upstream: https://lists.nongnu.org/archive/html/qemu-arm/2023-04/msg00549
+
+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
+