[Qemu-devel] [PATCH v3] hw/core/null-machine: Add the possibility to instantiate a CPU and RAM

[Thomas Huth]

Sometimes it is useful to have just a machine with CPU and RAM, without
any further hardware in it, e.g. if you just want to do some instruction
debugging for TCG with a remote GDB attached to QEMU, or run some embedded
code with the "-semihosting" QEMU parameter. qemu-system-m68k already
features a "dummy" machine, and xtensa a "sim" machine for exactly this
purpose.
All target architectures have nowadays also a "none" machine, which would
be a perfect match for this, too - but it currently does not allow to add
CPU and RAM yet. Thus let's add these possibilities in a generic way to the
"none" machine, too, so that we hopefully do not need additional "dummy"
machines in the future anymore (and maybe can also get rid of the already
existing "dummy"/"sim" machines one day).
Note that the default behaviour of the "none" machine is not changed, i.e.
no CPU and no RAM is instantiated by default. You have explicitely got to
specify the CPU model with "-cpu" and the amount of RAM with "-m" to get
these new features.

Signed-off-by: Thomas Huth <address@hidden>
---
 v3:
 - Get rid of the cpu_init_def() wrapper again, make null-machine.o
   target dependent instead and use cpu_init() directly.
 - Omit the loader code for the "-kernel" option for now (users can
   use "-device loader,..." instead). We can add code for the -kernel
   parameter later (either an implementation or a warning), once we've
   decided how it should behave for the "none" machine.

 hw/core/Makefile.objs  |  2 +-
 hw/core/null-machine.c | 27 +++++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/hw/core/Makefile.objs b/hw/core/Makefile.objs
index a4c94e5..0b6c0f1 100644
--- a/hw/core/Makefile.objs
+++ b/hw/core/Makefile.objs
@@ -12,7 +12,6 @@ common-obj-$(CONFIG_XILINX_AXI) += stream.o
 common-obj-$(CONFIG_PTIMER) += ptimer.o
 common-obj-$(CONFIG_SOFTMMU) += sysbus.o
 common-obj-$(CONFIG_SOFTMMU) += machine.o
-common-obj-$(CONFIG_SOFTMMU) += null-machine.o
 common-obj-$(CONFIG_SOFTMMU) += loader.o
 common-obj-$(CONFIG_SOFTMMU) += qdev-properties-system.o
 common-obj-$(CONFIG_SOFTMMU) += register.o
@@ -20,3 +19,4 @@ common-obj-$(CONFIG_SOFTMMU) += or-irq.o
 common-obj-$(CONFIG_PLATFORM_BUS) += platform-bus.o
 
 obj-$(CONFIG_SOFTMMU) += generic-loader.o
+obj-$(CONFIG_SOFTMMU) += null-machine.o
diff --git a/hw/core/null-machine.c b/hw/core/null-machine.c
index 0351ba7..27c8369 100644
--- a/hw/core/null-machine.c
+++ b/hw/core/null-machine.c
@@ -13,18 +13,41 @@
 
 #include "qemu/osdep.h"
 #include "qemu-common.h"
+#include "qemu/error-report.h"
 #include "hw/hw.h"
 #include "hw/boards.h"
+#include "sysemu/sysemu.h"
+#include "exec/address-spaces.h"
+#include "cpu.h"
 
-static void machine_none_init(MachineState *machine)
+static void machine_none_init(MachineState *mch)
 {
+    CPUState *cpu = NULL;
+
+    /* Initialize CPU (if a model has been specified) */
+    if (mch->cpu_model) {
+        cpu = cpu_init(mch->cpu_model);
+        if (!cpu) {
+            error_report("Unable to initialize CPU");
+            exit(1);
+        }
+    }
+
+    /* RAM at address zero */
+    if (mch->ram_size) {
+        MemoryRegion *ram = g_new(MemoryRegion, 1);
+
+        memory_region_allocate_system_memory(ram, NULL, "ram", mch->ram_size);
+        memory_region_add_subregion(get_system_memory(), 0, ram);
+    }
 }
 
 static void machine_none_machine_init(MachineClass *mc)
 {
     mc->desc = "empty machine";
     mc->init = machine_none_init;
-    mc->max_cpus = 0;
+    mc->max_cpus = 1;
+    mc->default_ram_size = 0;
 }
 
 DEFINE_MACHINE("none", machine_none_machine_init)
-- 
1.8.3.1