target-info: introduce TargetInfo in QOM

For the single-binary, we want to be able to retrieve at runtime the
current target among the different ones available.
A consequence is that we can't rely on existing target_info() definition
since it will create a conflict once more than one target is available.

To solve this, we add TargetInfo in QOM, with this hierarchy.
We define one class "target-info-X" per target, that inherits from
abstract class "target-info". Using concrete vs abstract class ensure we
can easily filter "target-info-X" from all QOM types.
Associated TargetInfo is directly set through class initialization,
without relying on any instance.

For user mode, we simply define target_info() like it was done
previously. In this patch, we keep the same definition for system-mode
also, and it will be replaced in next commits.

We will introduce detection of target from QOM, so we need to make sure
those types are registered early.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20260514172303.1484273-4-pierrick.bouvier@oss.qualcomm.com
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>

configs/targets/aarch64-softmmu.c

@@ -8,6 +8,7 @@
 
 #include "qemu/osdep.h"
 #include "qemu/target-info-impl.h"
+#include "qemu/target-info-init.h"
 #include "hw/arm/machines-qom.h"
 #include "target/arm/cpu-qom.h"
 #include "target/arm/cpu-param.h"
@@ -23,7 +24,4 @@ static const TargetInfo target_info_aarch64_system = {
     .page_bits_init = TARGET_PAGE_BITS_LEGACY,
 };
 
-const TargetInfo *target_info(void)
-{
-    return &target_info_aarch64_system;
-}
+target_info_init(target_info_aarch64_system)

configs/targets/arm-softmmu.c

@@ -8,6 +8,7 @@
 
 #include "qemu/osdep.h"
 #include "qemu/target-info-impl.h"
+#include "qemu/target-info-init.h"
 #include "hw/arm/machines-qom.h"
 #include "target/arm/cpu-qom.h"
 #include "target/arm/cpu-param.h"
@@ -23,7 +24,4 @@ static const TargetInfo target_info_arm_system = {
     .page_bits_init = TARGET_PAGE_BITS_LEGACY,
 };
 
-const TargetInfo *target_info(void)
-{
-    return &target_info_arm_system;
-}
+target_info_init(target_info_arm_system)

include/qemu/module.h

@@ -43,6 +43,7 @@ typedef enum {
     MODULE_INIT_MIGRATION,
     MODULE_INIT_BLOCK,
     MODULE_INIT_OPTS,
+    MODULE_INIT_TARGET_INFO,
     MODULE_INIT_QOM,
     MODULE_INIT_TRACE,
     MODULE_INIT_XEN_BACKEND,

include/qemu/target-info-init.h

@@ -0,0 +1,58 @@
+/*
+ * QEMU target info initialization
+ *
+ * Copyright (c) Qualcomm
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This file is included by each file defining a TargetInfo structure and is
+ * responsible for registering it.
+ */
+
+#ifndef QEMU_TARGET_INFO_INIT_H
+#define QEMU_TARGET_INFO_INIT_H
+
+#define DEFINE_TARGET_INFO_TYPE(info)                                       \
+static void do_qemu_init_target_info(void)                                  \
+{                                                                           \
+    type_register_static(&info);                                            \
+}                                                                           \
+module_init(do_qemu_init_target_info, MODULE_INIT_TARGET_INFO)
+
+#ifdef COMPILING_PER_TARGET
+#ifdef CONFIG_USER_ONLY
+
+/*
+ * User mode does not support multiple targets in the same binary, so just
+ * define target_info().
+ */
+#define target_info_init(ti_var)        \
+const TargetInfo *target_info(void)     \
+{                                       \
+    return &ti_var;                     \
+}
+
+#else /* CONFIG_USER_ONLY */
+
+#include "qemu/target-info-qom.h"
+#include "qom/object.h"
+
+#define target_info_init(ti_var)                                            \
+const TargetInfo *target_info(void)                                         \
+{                                                                           \
+    return &ti_var;                                                         \
+}                                                                           \
+                                                                            \
+static const TypeInfo target_info_qom_target_type_info = {                  \
+    .name =  TYPE_TARGET_INFO"-"TARGET_NAME,                                \
+    .parent = TYPE_TARGET_INFO,                                             \
+    .instance_size = sizeof(TargetInfoQom),                                 \
+    .class_size = sizeof(TargetInfoQomClass),                               \
+    .class_data = &ti_var,                                                  \
+};                                                                          \
+DEFINE_TARGET_INFO_TYPE(target_info_qom_target_type_info)
+
+#endif /* CONFIG_USER_ONLY */
+#endif /* COMPILING_PER_TARGET */
+
+#endif /* QEMU_TARGET_INFO_INIT_H */

include/qemu/target-info-qom.h

@@ -0,0 +1,28 @@
+/*
+ * QEMU target info QOM types
+ *
+ * Copyright (c) Qualcomm
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef QEMU_TARGET_INFO_QOM_H
+#define QEMU_TARGET_INFO_QOM_H
+
+#include "qemu/target-info-impl.h"
+#include "qom/object.h"
+
+#define TYPE_TARGET_INFO "target-info"
+
+typedef struct TargetInfoQom {
+    Object parent_obj;
+} TargetInfoQom;
+
+typedef struct TargetInfoQomClass {
+    ObjectClass parent_class;
+    const TargetInfo *target_info;
+} TargetInfoQomClass;
+
+OBJECT_DECLARE_TYPE(TargetInfoQom, TargetInfoQomClass, TARGET_INFO)
+
+#endif /* QEMU_TARGET_INFO_QOM_H */

system/vl.c

@@ -2889,6 +2889,8 @@ void qemu_init(int argc, char **argv)
 
     os_setup_limits();
 
+    module_call_init(MODULE_INIT_TARGET_INFO);
+
     module_init_info(qemu_modinfo);
     module_allow_arch(target_name());
 

target-info-qom.c

@@ -7,7 +7,11 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 #include "qom/object.h"
+#include "qemu/target-info-impl.h"
+#include "qemu/target-info-init.h"
+#include "qemu/target-info-qom.h"
 #include "hw/arm/machines-qom.h"
 
 static const TypeInfo target_info_types[] = {
@@ -22,3 +26,23 @@ static const TypeInfo target_info_types[] = {
 };
 
 DEFINE_TYPES(target_info_types)
+
+static void target_info_qom_class_init(ObjectClass *oc, const void * data)
+{
+    TargetInfoQomClass *klass = TARGET_INFO_CLASS(oc);
+    klass->target_info = data;
+}
+
+static const TypeInfo target_info_parent_type = {
+    .name = TYPE_TARGET_INFO,
+    .parent = TYPE_OBJECT,
+    .instance_size = sizeof(TargetInfoQom),
+    .class_size = sizeof(TargetInfoQomClass),
+    /* use class_base_init so children classes can set class_data accordingly */
+    .class_base_init = target_info_qom_class_init,
+    /* children classes will be concrete, which allows to easily query them
+     * without listing this parent class also */
+    .abstract = true,
+};
+
+DEFINE_TARGET_INFO_TYPE(target_info_parent_type)

target-info-stub.c

@@ -9,6 +9,7 @@
 #include "qemu/osdep.h"
 #include "qemu/target-info.h"
 #include "qemu/target-info-impl.h"
+#include "qemu/target-info-init.h"
 #include "hw/core/boards.h"
 #include "cpu.h"
 #include "exec/cpu-defs.h"
@@ -41,7 +42,4 @@ static const TargetInfo target_info_stub = {
 #endif
 };
 
-const TargetInfo *target_info(void)
-{
-    return &target_info_stub;
-}
+target_info_init(target_info_stub)

tests/qtest/fuzz/fuzz.c

@@ -172,6 +172,7 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp)
 
     /* Initialize qgraph and modules */
     qos_graph_init();
+    module_call_init(MODULE_INIT_TARGET_INFO);
     module_call_init(MODULE_INIT_FUZZ_TARGET);
     module_call_init(MODULE_INIT_QOM);
     module_call_init(MODULE_INIT_LIBQOS);