plugins/stoptrigger: TCG plugin to stop execution under conditions

This new plugin allows to stop emulation using conditions on the
emulation state. By setting this plugin arguments, it is possible
to set an instruction count limit and/or trigger address(es) to stop at.
The code returned at emulation exit can be customized.

This plugin demonstrates how someone could stop QEMU execution.
It could be used for research purposes to launch some code and
deterministically stop it and understand where its execution flow went.

Co-authored-by: Alexandre Iooss <erdnaxe@crans.org>
Signed-off-by: Simon Hamelin <simon.hamelin@grenoble-inp.org>
Signed-off-by: Alexandre Iooss <erdnaxe@crans.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240715081521.19122-2-simon.hamelin@grenoble-inp.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240718094523.1198645-5-alex.bennee@linaro.org>

2 files changed, 152 insertions, 0 deletions

diff --git a/contrib/plugins/Makefile b/contrib/plugins/Makefile
index 449ead1130..98a89d5c40 100644
--- a/contrib/plugins/Makefile
+++ b/contrib/plugins/Makefile
@@ -28,6 +28,7 @@ NAMES += hwprofile
 NAMES += cache
 NAMES += drcov
 NAMES += ips
+NAMES += stoptrigger
 
 ifeq ($(CONFIG_WIN32),y)
 SO_SUFFIX := .dll
diff --git a/contrib/plugins/stoptrigger.c b/contrib/plugins/stoptrigger.c
new file mode 100644
index 0000000000..03ee22f4c6
--- /dev/null
+++ b/contrib/plugins/stoptrigger.c
@@ -0,0 +1,151 @@
+/*
+ * Copyright (C) 2024, Simon Hamelin <simon.hamelin@grenoble-inp.org>
+ *
+ * Stop execution once a given address is reached or if the
+ * count of executed instructions reached a specified limit
+ *
+ * License: GNU GPL, version 2 or later.
+ *   See the COPYING file in the top-level directory.
+ */
+
+#include <assert.h>
+#include <glib.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <qemu-plugin.h>
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+
+/* Scoreboard to track executed instructions count */
+typedef struct {
+    uint64_t insn_count;
+} InstructionsCount;
+static struct qemu_plugin_scoreboard *insn_count_sb;
+static qemu_plugin_u64 insn_count;
+
+static uint64_t icount;
+static int icount_exit_code;
+
+static bool exit_on_icount;
+static bool exit_on_address;
+
+/* Map trigger addresses to exit code */
+static GHashTable *addrs_ht;
+
+static void exit_emulation(int return_code, char *message)
+{
+    qemu_plugin_outs(message);
+    g_free(message);
+    exit(return_code);
+}
+
+static void exit_icount_reached(unsigned int cpu_index, void *udata)
+{
+    uint64_t insn_vaddr = GPOINTER_TO_UINT(udata);
+    char *msg = g_strdup_printf("icount reached at 0x%" PRIx64 ", exiting\n",
+                                insn_vaddr);
+
+    exit_emulation(icount_exit_code, msg);
+}
+
+static void exit_address_reached(unsigned int cpu_index, void *udata)
+{
+    uint64_t insn_vaddr = GPOINTER_TO_UINT(udata);
+    char *msg = g_strdup_printf("0x%" PRIx64 " reached, exiting\n", insn_vaddr);
+    int exit_code;
+
+    exit_code = GPOINTER_TO_INT(
+        g_hash_table_lookup(addrs_ht, GUINT_TO_POINTER(insn_vaddr)));
+
+    exit_emulation(exit_code, msg);
+}
+
+static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    size_t tb_n = qemu_plugin_tb_n_insns(tb);
+    for (size_t i = 0; i < tb_n; i++) {
+        struct qemu_plugin_insn *insn = qemu_plugin_tb_get_insn(tb, i);
+        gpointer insn_vaddr = GUINT_TO_POINTER(qemu_plugin_insn_vaddr(insn));
+
+        if (exit_on_icount) {
+            /* Increment and check scoreboard for each instruction */
+            qemu_plugin_register_vcpu_insn_exec_inline_per_vcpu(
+                insn, QEMU_PLUGIN_INLINE_ADD_U64, insn_count, 1);
+            qemu_plugin_register_vcpu_insn_exec_cond_cb(
+                insn, exit_icount_reached, QEMU_PLUGIN_CB_NO_REGS,
+                QEMU_PLUGIN_COND_EQ, insn_count, icount + 1, insn_vaddr);
+        }
+
+        if (exit_on_address) {
+            if (g_hash_table_contains(addrs_ht, insn_vaddr)) {
+                /* Exit triggered by address */
+                qemu_plugin_register_vcpu_insn_exec_cb(
+                    insn, exit_address_reached, QEMU_PLUGIN_CB_NO_REGS,
+                    insn_vaddr);
+            }
+        }
+    }
+}
+
+static void plugin_exit(qemu_plugin_id_t id, void *p)
+{
+    g_hash_table_destroy(addrs_ht);
+    qemu_plugin_scoreboard_free(insn_count_sb);
+}
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
+                                           const qemu_info_t *info, int argc,
+                                           char **argv)
+{
+    addrs_ht = g_hash_table_new(NULL, g_direct_equal);
+
+    insn_count_sb = qemu_plugin_scoreboard_new(sizeof(InstructionsCount));
+    insn_count = qemu_plugin_scoreboard_u64_in_struct(
+        insn_count_sb, InstructionsCount, insn_count);
+
+    for (int i = 0; i < argc; i++) {
+        char *opt = argv[i];
+        g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
+        if (g_strcmp0(tokens[0], "icount") == 0) {
+            g_auto(GStrv) icount_tokens = g_strsplit(tokens[1], ":", 2);
+            icount = g_ascii_strtoull(icount_tokens[0], NULL, 0);
+            if (icount < 1 || g_strrstr(icount_tokens[0], "-") != NULL) {
+                fprintf(stderr,
+                        "icount parsing failed: '%s' must be a positive "
+                        "integer\n",
+                        icount_tokens[0]);
+                return -1;
+            }
+            if (icount_tokens[1]) {
+                icount_exit_code = g_ascii_strtoull(icount_tokens[1], NULL, 0);
+            }
+            exit_on_icount = true;
+        } else if (g_strcmp0(tokens[0], "addr") == 0) {
+            g_auto(GStrv) addr_tokens = g_strsplit(tokens[1], ":", 2);
+            uint64_t exit_addr = g_ascii_strtoull(addr_tokens[0], NULL, 0);
+            int exit_code = 0;
+            if (addr_tokens[1]) {
+                exit_code = g_ascii_strtoull(addr_tokens[1], NULL, 0);
+            }
+            g_hash_table_insert(addrs_ht, GUINT_TO_POINTER(exit_addr),
+                                GINT_TO_POINTER(exit_code));
+            exit_on_address = true;
+        } else {
+            fprintf(stderr, "option parsing failed: %s\n", opt);
+            return -1;
+        }
+    }
+
+    if (!exit_on_icount && !exit_on_address) {
+        fprintf(stderr, "'icount' or 'addr' argument missing\n");
+        return -1;
+    }
+
+    /* Register translation block and exit callbacks */
+    qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+
+    return 0;
+}