plugins: add PC diversion API function

This patch adds a plugin API function that allows diverting the program
counter during execution. A potential use case for this functionality is
to skip over parts of the code, e.g., by hooking into a specific
instruction and setting the PC to the next instruction in the callback.

Link: https://lists.nongnu.org/archive/html/qemu-devel/2025-08/msg00656.html
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Florian Hofhammer <florian.hofhammer@epfl.ch>
Link: https://lore.kernel.org/qemu-devel/20260305-setpc-v5-v7-4-4c3adba52403@epfl.ch
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>

include/plugins/qemu-plugin.h

@@ -76,6 +76,7 @@ typedef uint64_t qemu_plugin_id_t;
  *
  * version 6:
  * - changed return value of qemu_plugin_{read,write}_register from int to bool
+ * - added qemu_plugin_set_pc
  */
 
 extern QEMU_PLUGIN_EXPORT int qemu_plugin_version;
@@ -1042,6 +1043,18 @@ QEMU_PLUGIN_API
 bool qemu_plugin_write_register(struct qemu_plugin_register *handle,
                                 GByteArray *buf);
 
+/**
+ * qemu_plugin_set_pc() - set the program counter for the current vCPU
+ *
+ * @vaddr: the new virtual (guest) address for the program counter
+ *
+ * This function sets the program counter for the current vCPU to @vaddr and
+ * resumes execution at that address. This function does not return.
+ */
+QEMU_PLUGIN_API
+__attribute__((__noreturn__))
+void qemu_plugin_set_pc(uint64_t vaddr);
+
 /**
  * qemu_plugin_read_memory_vaddr() - read from memory using a virtual address
  *

plugins/api.c

@@ -41,6 +41,7 @@
 #include "qemu/log.h"
 #include "system/memory.h"
 #include "tcg/tcg.h"
+#include "exec/cpu-common.h"
 #include "exec/gdbstub.h"
 #include "exec/target_page.h"
 #include "exec/translation-block.h"
@@ -467,6 +468,16 @@ bool qemu_plugin_write_register(struct qemu_plugin_register *reg,
     return (gdb_write_register(current_cpu, buf->data, GPOINTER_TO_INT(reg) - 1) > 0);
 }
 
+void qemu_plugin_set_pc(uint64_t vaddr)
+{
+    g_assert(current_cpu);
+
+    g_assert(qemu_plugin_get_cb_flags() == QEMU_PLUGIN_CB_RW_REGS_PC);
+
+    cpu_set_pc(current_cpu, vaddr);
+    cpu_loop_exit(current_cpu);
+}
+
 bool qemu_plugin_read_memory_vaddr(uint64_t addr, GByteArray *data, size_t len)
 {
     g_assert(current_cpu);

scripts/qemu-plugin-symbols.py

@@ -20,9 +20,14 @@ def extract_symbols(plugin_header):
     # Remove QEMU_PLUGIN_API macro definition.
     content = content.replace('#define QEMU_PLUGIN_API', '')
     expected = content.count('QEMU_PLUGIN_API')
-    # Find last word between QEMU_PLUGIN_API and (, matching on several lines.
+    # Find last word between QEMU_PLUGIN_API and ( to get the function name,
+    # matching on several lines. Discard attributes, if any.
     # We use *? non-greedy quantifier.
-    syms = re.findall(r'QEMU_PLUGIN_API.*?(\w+)\s*\(', content, re.DOTALL)
+    syms = re.findall(
+        r'QEMU_PLUGIN_API\s+(?:__attribute__\(\(\S+\)\))?.*?(\w+)\s*\(',
+        content,
+        re.DOTALL,
+    )
     syms.sort()
     # Ensure we found as many symbols as API markers.
     assert len(syms) == expected