[PATCH v3 2/8] Add register write API

[Rowan Hart <rowanbhart@gmail.com>]

From: novafacing <rowanbhart@gmail.com>

Signed-off-by: novafacing <rowanbhart@gmail.com>
Signed-off-by: Rowan Hart <rowanbhart@gmail.com>
---
 include/qemu/qemu-plugin.h | 57 +++++++++++++++++++++++++-------------
 plugins/api.c              | 26 ++++++++++++-----
 2 files changed, 56 insertions(+), 27 deletions(-)

diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
index 3a850aa216..68c8632fd7 100644
--- a/include/qemu/qemu-plugin.h
+++ b/include/qemu/qemu-plugin.h
@@ -254,9 +254,6 @@ typedef struct {
  * @QEMU_PLUGIN_CB_NO_REGS: callback does not access the CPU's regs
  * @QEMU_PLUGIN_CB_R_REGS: callback reads the CPU's regs
  * @QEMU_PLUGIN_CB_RW_REGS: callback reads and writes the CPU's regs
- *
- * Note: currently QEMU_PLUGIN_CB_RW_REGS is unused, plugins cannot change
- * system register state.
  */
 enum qemu_plugin_cb_flags {
     QEMU_PLUGIN_CB_NO_REGS,
@@ -871,7 +868,8 @@ struct qemu_plugin_register;
 /**
  * typedef qemu_plugin_reg_descriptor - register descriptions
  *
- * @handle: opaque handle for retrieving value with qemu_plugin_read_register
+ * @handle: opaque handle for retrieving value with qemu_plugin_read_register or
+ *          writing value with qemu_plugin_write_register
  * @name: register name
  * @feature: optional feature descriptor, can be NULL
  */
@@ -893,6 +891,41 @@ typedef struct {
 QEMU_PLUGIN_API
 GArray *qemu_plugin_get_registers(void);
 
+/**
+ * qemu_plugin_read_register() - read register for current vCPU
+ *
+ * @handle: a @qemu_plugin_reg_handle handle
+ * @buf: A GByteArray for the data owned by the plugin
+ *
+ * This function is only available in a context that register read access is
+ * explicitly requested via the QEMU_PLUGIN_CB_R_REGS flag.
+ *
+ * Returns the size of the read register. The content of @buf is in target byte
+ * order. On failure returns -1.
+ */
+QEMU_PLUGIN_API
+int qemu_plugin_read_register(struct qemu_plugin_register *handle,
+                              GByteArray *buf);
+
+/**
+ * qemu_plugin_write_register() - write register for current vCPU
+ *
+ * @handle: a @qemu_plugin_reg_handle handle
+ * @buf: A GByteArray for the data owned by the plugin
+ *
+ * This function is only available in a context that register write access is
+ * explicitly requested via the QEMU_PLUGIN_CB_W_REGS flag.
+ *
+ * The size of @buf must be at least the size of the requested register.
+ * Attempting to write a register with @buf smaller than the register size
+ * will result in a crash or other undesired behavior.
+ *
+ * Returns the number of bytes written. On failure returns 0.
+ */
+QEMU_PLUGIN_API
+int qemu_plugin_write_register(struct qemu_plugin_register *handle,
+                              GByteArray *buf);
+
 /**
  * qemu_plugin_read_memory_vaddr() - read from memory using a virtual address
  *
@@ -915,22 +948,6 @@ QEMU_PLUGIN_API
 bool qemu_plugin_read_memory_vaddr(uint64_t addr,
                                    GByteArray *data, size_t len);
 
-/**
- * qemu_plugin_read_register() - read register for current vCPU
- *
- * @handle: a @qemu_plugin_reg_handle handle
- * @buf: A GByteArray for the data owned by the plugin
- *
- * This function is only available in a context that register read access is
- * explicitly requested via the QEMU_PLUGIN_CB_R_REGS flag.
- *
- * Returns the size of the read register. The content of @buf is in target byte
- * order. On failure returns -1.
- */
-QEMU_PLUGIN_API
-int qemu_plugin_read_register(struct qemu_plugin_register *handle,
-                              GByteArray *buf);
-
 /**
  * qemu_plugin_scoreboard_new() - alloc a new scoreboard
  *
diff --git a/plugins/api.c b/plugins/api.c
index 3c9d4832e9..79b2dc20b8 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -433,6 +433,25 @@ GArray *qemu_plugin_get_registers(void)
     return create_register_handles(regs);
 }
 
+int qemu_plugin_read_register(struct qemu_plugin_register *reg, GByteArray *buf)
+{
+    g_assert(current_cpu);
+
+    return gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) - 1);
+}
+
+int qemu_plugin_write_register(struct qemu_plugin_register *reg, 
+                               GByteArray *buf)
+{
+    g_assert(current_cpu);
+
+    if (buf->len == 0) {
+        return 0;
+    }
+
+    return gdb_write_register(current_cpu, buf->data, GPOINTER_TO_INT(reg) - 1);
+}
+
 bool qemu_plugin_read_memory_vaddr(uint64_t addr, GByteArray *data, size_t len)
 {
     g_assert(current_cpu);
@@ -453,13 +472,6 @@ bool qemu_plugin_read_memory_vaddr(uint64_t addr, GByteArray *data, size_t len)
     return true;
 }
 
-int qemu_plugin_read_register(struct qemu_plugin_register *reg, GByteArray *buf)
-{
-    g_assert(current_cpu);
-
-    return gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) - 1);
-}
-
 struct qemu_plugin_scoreboard *qemu_plugin_scoreboard_new(size_t element_size)
 {
     return plugin_scoreboard_new(element_size);
-- 
2.49.0