[PATCH v17 13/14] plugins: Allow to read registers

[Akihiko Odaki <akihiko.odaki@daynix.com>]

It is based on GDB protocol to ensure interface stability.

The timing of the vcpu init hook is also changed so that the hook will
get called after GDB features are initialized.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1706
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 include/qemu/qemu-plugin.h   | 50 ++++++++++++++++++++++++++++++++++++++++++--
 plugins/api.c                | 20 ++++++++++++++++++
 plugins/qemu-plugins.symbols |  3 +++
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
index 4daab6efd291..e7e21c9ee5b7 100644
--- a/include/qemu/qemu-plugin.h
+++ b/include/qemu/qemu-plugin.h
@@ -11,6 +11,7 @@
 #ifndef QEMU_QEMU_PLUGIN_H
 #define QEMU_QEMU_PLUGIN_H
 
+#include <glib.h>
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stddef.h>
@@ -227,8 +228,8 @@ struct qemu_plugin_insn;
  * @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 unused, plugins cannot read or change system
- * register state.
+ * 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,
@@ -708,4 +709,49 @@ uint64_t qemu_plugin_end_code(void);
 QEMU_PLUGIN_API
 uint64_t qemu_plugin_entry_code(void);
 
+/**
+ * qemu_plugin_find_register_file() - find register file
+ *
+ * @vcpu_index: the index of the vcpu context
+ * @name: the name of the register file.
+ *
+ * Returns the identifier of the register file if it was found, and a negative
+ * value otherwise.
+ *
+ * The names of register files are identical with names of GDB's standard
+ * target features with some extensions. For details, see:
+ * https://sourceware.org/gdb/onlinedocs/gdb/Standard-Target-Features.html
+ */
+int qemu_plugin_find_register_file(unsigned int vcpu_index, const char *name);
+
+/**
+ * qemu_plugin_find_register() - find register
+ *
+ * @vcpu_index: the index of the vcpu context
+ * @file: the register file identifier determined with
+ *        qemu_plugin_find_register_file().
+ * @name: the name of the register.
+ *
+ * The names of register are identical with names used in GDB's standard
+ * target features with some extensions. For details, see:
+ * https://sourceware.org/gdb/onlinedocs/gdb/Standard-Target-Features.html
+ */
+int qemu_plugin_find_register(unsigned int vcpu_index, int file,
+                              const char *name);
+
+/**
+ * qemu_plugin_read_register() - read register
+ *
+ * @buf: the byte array to append the read register content to.
+ * @reg: the register identifier determined with
+ *       qemu_plugin_find_register().
+ *
+ * This function is only available in a context that register read access is
+ * explicitly requested.
+ *
+ * Returns the size of the read register. The content of @buf is in target byte
+ * order.
+ */
+int qemu_plugin_read_register(GByteArray *buf, int reg);
+
 #endif /* QEMU_QEMU_PLUGIN_H */
diff --git a/plugins/api.c b/plugins/api.c
index ac39cdea0b35..3eaad5bf4187 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -35,10 +35,12 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/main-loop.h"
 #include "qemu/plugin.h"
 #include "qemu/log.h"
 #include "tcg/tcg.h"
 #include "exec/exec-all.h"
+#include "exec/gdbstub.h"
 #include "exec/ram_addr.h"
 #include "disas/disas.h"
 #include "plugin.h"
@@ -435,3 +437,21 @@ uint64_t qemu_plugin_entry_code(void)
 #endif
     return entry;
 }
+
+int qemu_plugin_find_register_file(unsigned int vcpu_index, const char *name)
+{
+    QEMU_IOTHREAD_LOCK_GUARD();
+    return gdb_find_feature(qemu_get_cpu(vcpu_index), name);
+}
+
+int qemu_plugin_find_register(unsigned int vcpu_index, int file,
+                              const char *name)
+{
+    QEMU_IOTHREAD_LOCK_GUARD();
+    return gdb_find_feature_register(qemu_get_cpu(vcpu_index), file, name);
+}
+
+int qemu_plugin_read_register(GByteArray *buf, int reg)
+{
+    return gdb_read_register(current_cpu, buf, reg);
+}
diff --git a/plugins/qemu-plugins.symbols b/plugins/qemu-plugins.symbols
index 71f6c90549d4..977f1fcfcbfb 100644
--- a/plugins/qemu-plugins.symbols
+++ b/plugins/qemu-plugins.symbols
@@ -42,4 +42,7 @@
   qemu_plugin_tb_vaddr;
   qemu_plugin_uninstall;
   qemu_plugin_vcpu_for_each;
+  qemu_plugin_find_register_file;
+  qemu_plugin_find_register;
+  qemu_plugin_read_register;
 };

-- 
2.43.0