plugins: Add enforcement of QEMU_PLUGIN_CB flags in register R/W callbacks

This patch adds functionality to enforce the requested QEMU_PLUGIN_CB_
flags level passed when registering a callback function using the
plugins API. Each time a callback is about to be invoked, a thread-local
variable will be updated with the level that callback requested. Then,
called API functions (in particular, the register read and write API)
will call qemu_plugin_get_cb_flags() to check the level is at least the
level they require.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Rowan Hart <rowanbhart@gmail.com>
Message-ID: <20250624175351.440780-4-rowanbhart@gmail.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20250627112512.1880708-8-alex.bennee@linaro.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/plugins/api.c b/plugins/api.c
index 6514f2c76a..3f04399c26 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -437,6 +437,10 @@ int qemu_plugin_read_register(struct qemu_plugin_register *reg, GByteArray *buf)
 {
     g_assert(current_cpu);
 
+    if (qemu_plugin_get_cb_flags() == QEMU_PLUGIN_CB_NO_REGS) {
+        return -1;
+    }
+
     return gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) - 1);
 }