On 2024/01/18 20:38, Alex Bennée wrote:
Akihiko Odaki <akihiko.od...@daynix.com> writes:
On 2024/01/16 19:48, Alex Bennée wrote:
We can only request a list of registers once the vCPU has been
initialised so the user needs to use either call the get function on
vCPU initialisation or during the translation phase.
We don't expose the reg number to the plugin instead hiding it
behind
an opaque handle. This allows for a bit of future proofing should the
internals need to be changed while also being hashed against the
CPUClass so we can handle different register sets per-vCPU in
hetrogenous situations.
Having an internal state within the plugins also allows us to expand
the interface in future (for example providing callbacks on register
change if the translator can track changes).
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1706
Cc: Akihiko Odaki <akihiko.od...@daynix.com>
Message-Id: <20240103173349.398526-39-alex.ben...@linaro.org>
Based-on: <20231025093128.33116-18-akihiko.od...@daynix.com>
Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouv...@linaro.org>
diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
index 4daab6efd29..2c1930e7e45 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 +709,50 @@ uint64_t qemu_plugin_end_code(void);
QEMU_PLUGIN_API
uint64_t qemu_plugin_entry_code(void);
+/** struct qemu_plugin_register - Opaque handle for register
access */
+struct qemu_plugin_register;
+
+/**
+ * typedef qemu_plugin_reg_descriptor - register descriptions
+ *
+ * @handle: opaque handle for retrieving value with qemu_plugin_read_register
+ * @name: register name
+ * @feature: optional feature descriptor, can be NULL
+ */
+typedef struct {
+ struct qemu_plugin_register *handle;
+ const char *name;
+ const char *feature;
+} qemu_plugin_reg_descriptor;
+
+/**
+ * qemu_plugin_get_registers() - return register list for vCPU
+ * @vcpu_index: vcpu to query
+ *
+ * Returns a GArray of qemu_plugin_reg_descriptor or NULL. Caller
+ * frees the array (but not the const strings).
+ *
+ * Should be used from a qemu_plugin_register_vcpu_init_cb() callback
+ * after the vCPU is initialised.
+ */
+GArray *qemu_plugin_get_registers(unsigned int vcpu_index);
+
+/**
+ * qemu_plugin_read_register() - read register
+ *
+ * @vcpu: vcpu index
+ * @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.
+ *
+ * Returns the size of the read register. The content of @buf is in target byte
+ * order. On failure returns -1
+ */
+int qemu_plugin_read_register(unsigned int vcpu,
+ struct qemu_plugin_register *handle,
+ GByteArray *buf);
+
+
#endif /* QEMU_QEMU_PLUGIN_H */
diff --git a/plugins/api.c b/plugins/api.c
index ac39cdea0b3..8d5cca53295 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -8,6 +8,7 @@
*
* qemu_plugin_tb
* qemu_plugin_insn
+ * qemu_plugin_register
*
* Which can then be passed back into the API to do additional things.
* As such all the public functions in here are exported in
@@ -35,10 +36,12 @@
*/
#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 +438,111 @@ uint64_t qemu_plugin_entry_code(void)
#endif
return entry;
}
+
+/*
+ * Register handles
+ *
+ * The plugin infrastructure keeps hold of these internal data
+ * structures which are presented to plugins as opaque handles. They
+ * are global to the system and therefor additions to the hash table
+ * must be protected by the @reg_handle_lock.
The BQL should be used instead. This lock only serializes the plugin
access, but the whole gdbstub code needs to be serialized to ensure
the correct behaving of e.g., gdb_get_register_list().
Why does gdb_get_register_list need to take the BQL? It only works
through per-cpu structures. The reg_handle_lock only protects the hash
table itself.
+ *
+ * In order to future proof for up-coming heterogeneous work we want
+ * different entries for each CPU type while sharing them in the
+ * common case of multiple cores of the same type.
I don't think such an effort should be done in the plugin code, but it
should be done in the common gdbstub code.
Sure - we can always move it later.
GDB assumes all threads have the same set of registers, so gdbstub
will need to take care of them by running distinct GDB servers for
each processor type, for example. There is a good chance that gdbstub
will duplicate similar logic.
Which logic?
reg_handles, a GHashTable, is used to detect the duplicate definitions
of a register in processors with same type, but such a logic is probably
better off to be implemented in gdbstub; gdbstub should have one
definition of register set for each type of processors in a system, and
gdbstub can use it to start a distinct GDB server for the type. This
way, gdbstub can ensure it exposes a homogeneous view for each GDB
server as GDB requires.
If gdbstub already has such a logic, the plugin infrastructure can just
query gdbstub for a common, shared register set used for a processor
type; it will no longer have to check for duplicate definitions with a
hash table.
