On 2024/02/20 23:14, Alex Bennée wrote:
Akihiko Odaki <akihiko.odaki@daynix.com> writes:
On 2024/02/17 1:30, 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.odaki@daynix.com>
Message-Id: <20240103173349.398526-39-alex.bennee@linaro.org>
Based-on: <20231025093128.33116-18-akihiko.odaki@daynix.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
<snip>
+/*
+ * 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.
+ *
+ * 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.
+ */
+
+static QemuMutex reg_handle_lock;
+
+struct qemu_plugin_register {
+ const char *name;
+ int gdb_reg_num;
+};
+
+static GHashTable *reg_handles; /* hash table of PluginReg */
+
+/* Generate a stable key - would xxhash be overkill? */
+static gpointer cpu_plus_reg_to_key(CPUState *cs, int gdb_regnum)
+{
+ uintptr_t key = (uintptr_t) cs->cc;
+ key ^= gdb_regnum;
+ return GUINT_TO_POINTER(key);
+}
I have pointed out this is theoretically prone to collisions and
unsafe.
How is it unsafe? The aim is to share handles for the same CPUClass
rather than having a unique handle per register/cpu combo.
THe intention is legitimate, but the implementation is not safe. It
assumes (uintptr)cs->cc ^ gdb_regnum is unique, but there is no such
guarantee. The key of GHashTable must be unique; generating hashes of
keys should be done with hash_func given to g_hash_table_new().