contrib/plugins: Add a plugin to generate basic block vectors

SimPoint is a widely used tool to find the ideal microarchitecture
simulation points so Valgrind[2] and Pin[3] support generating basic
block vectors for use with them. Let's add a corresponding plugin to
QEMU too.

Note that this plugin has a different goal with tests/plugin/bb.c.

This plugin creates a vector for each constant interval instead of
counting the execution of basic blocks for the entire run and able to
describe the change of execution behavior. Its output is also
syntactically simple and better suited for parsing, while the output of
tests/plugin/bb.c is more human-readable.

[1] https://cseweb.ucsd.edu/~calder/simpoint/
[2] https://valgrind.org/docs/manual/bbv-manual.html
[3] https://www.intel.com/content/www/us/en/developer/articles/tool/pin-a-dynamic-binary-instrumentation-tool.html

Signed-off-by: Yotaro Nada <yotaro.nada@gmail.com>
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240816-bb-v3-1-b9aa4a5c75c5@daynix.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240916085400.1046925-16-alex.bennee@linaro.org>

3 files changed, 189 insertions, 0 deletions

diff --git a/contrib/plugins/Makefile b/contrib/plugins/Makefile
index d4ac599f93..bbddd4800f 100644
--- a/contrib/plugins/Makefile
+++ b/contrib/plugins/Makefile
@@ -13,6 +13,7 @@ TOP_SRC_PATH = $(SRC_PATH)/../..
 VPATH += $(SRC_PATH)
 
 NAMES :=
+NAMES += bbv
 NAMES += execlog
 NAMES += hotblocks
 NAMES += hotpages
diff --git a/contrib/plugins/bbv.c b/contrib/plugins/bbv.c
new file mode 100644
index 0000000000..a5256517dd
--- /dev/null
+++ b/contrib/plugins/bbv.c
@@ -0,0 +1,158 @@
+/*
+ * Generate basic block vectors for use with the SimPoint analysis tool.
+ * SimPoint: https://cseweb.ucsd.edu/~calder/simpoint/
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <stdio.h>
+#include <glib.h>
+
+#include <qemu-plugin.h>
+
+typedef struct Bb {
+    uint64_t vaddr;
+    struct qemu_plugin_scoreboard *count;
+    unsigned int index;
+} Bb;
+
+typedef struct Vcpu {
+    uint64_t count;
+    FILE *file;
+} Vcpu;
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+static GHashTable *bbs;
+static GRWLock bbs_lock;
+static char *filename;
+static struct qemu_plugin_scoreboard *vcpus;
+static uint64_t interval = 100000000;
+
+static void plugin_exit(qemu_plugin_id_t id, void *p)
+{
+    for (int i = 0; i < qemu_plugin_num_vcpus(); i++) {
+        fclose(((Vcpu *)qemu_plugin_scoreboard_find(vcpus, i))->file);
+    }
+
+    g_hash_table_unref(bbs);
+    g_free(filename);
+    qemu_plugin_scoreboard_free(vcpus);
+}
+
+static void free_bb(void *data)
+{
+    qemu_plugin_scoreboard_free(((Bb *)data)->count);
+    g_free(data);
+}
+
+static qemu_plugin_u64 count_u64(void)
+{
+    return qemu_plugin_scoreboard_u64_in_struct(vcpus, Vcpu, count);
+}
+
+static qemu_plugin_u64 bb_count_u64(Bb *bb)
+{
+    return qemu_plugin_scoreboard_u64(bb->count);
+}
+
+static void vcpu_init(qemu_plugin_id_t id, unsigned int vcpu_index)
+{
+    g_autofree gchar *vcpu_filename = NULL;
+    Vcpu *vcpu = qemu_plugin_scoreboard_find(vcpus, vcpu_index);
+
+    vcpu_filename = g_strdup_printf("%s.%u.bb", filename, vcpu_index);
+    vcpu->file = fopen(vcpu_filename, "w");
+}
+
+static void vcpu_interval_exec(unsigned int vcpu_index, void *udata)
+{
+    Vcpu *vcpu = qemu_plugin_scoreboard_find(vcpus, vcpu_index);
+    GHashTableIter iter;
+    void *value;
+
+    if (!vcpu->file) {
+        return;
+    }
+
+    vcpu->count -= interval;
+
+    fputc('T', vcpu->file);
+
+    g_rw_lock_reader_lock(&bbs_lock);
+    g_hash_table_iter_init(&iter, bbs);
+
+    while (g_hash_table_iter_next(&iter, NULL, &value)) {
+        Bb *bb = value;
+        uint64_t bb_count = qemu_plugin_u64_get(bb_count_u64(bb), vcpu_index);
+
+        if (!bb_count) {
+            continue;
+        }
+
+        fprintf(vcpu->file, ":%u:%" PRIu64 " ", bb->index, bb_count);
+        qemu_plugin_u64_set(bb_count_u64(bb), vcpu_index, 0);
+    }
+
+    g_rw_lock_reader_unlock(&bbs_lock);
+    fputc('\n', vcpu->file);
+}
+
+static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    uint64_t n_insns = qemu_plugin_tb_n_insns(tb);
+    uint64_t vaddr = qemu_plugin_tb_vaddr(tb);
+    Bb *bb;
+
+    g_rw_lock_writer_lock(&bbs_lock);
+    bb = g_hash_table_lookup(bbs, &vaddr);
+    if (!bb) {
+        bb = g_new(Bb, 1);
+        bb->vaddr = vaddr;
+        bb->count = qemu_plugin_scoreboard_new(sizeof(uint64_t));
+        bb->index = g_hash_table_size(bbs);
+        g_hash_table_replace(bbs, &bb->vaddr, bb);
+    }
+    g_rw_lock_writer_unlock(&bbs_lock);
+
+    qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
+        tb, QEMU_PLUGIN_INLINE_ADD_U64, count_u64(), n_insns);
+
+    qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
+        tb, QEMU_PLUGIN_INLINE_ADD_U64, bb_count_u64(bb), n_insns);
+
+    qemu_plugin_register_vcpu_tb_exec_cond_cb(
+        tb, vcpu_interval_exec, QEMU_PLUGIN_CB_NO_REGS,
+        QEMU_PLUGIN_COND_GE, count_u64(), interval, NULL);
+}
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
+                                           const qemu_info_t *info,
+                                           int argc, char **argv)
+{
+    for (int i = 0; i < argc; i++) {
+        char *opt = argv[i];
+        g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
+        if (g_strcmp0(tokens[0], "interval") == 0) {
+            interval = g_ascii_strtoull(tokens[1], NULL, 10);
+        } else if (g_strcmp0(tokens[0], "outfile") == 0) {
+            filename = tokens[1];
+            tokens[1] = NULL;
+        } else {
+            fprintf(stderr, "option parsing failed: %s\n", opt);
+            return -1;
+        }
+    }
+
+    if (!filename) {
+        fputs("outfile unspecified\n", stderr);
+        return -1;
+    }
+
+    bbs = g_hash_table_new_full(g_int64_hash, g_int64_equal, NULL, free_bb);
+    vcpus = qemu_plugin_scoreboard_new(sizeof(Vcpu));
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+    qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
+    qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
+
+    return 0;
+}
diff --git a/docs/about/emulation.rst b/docs/about/emulation.rst
index 05f54d3f27..ee59c2fa9b 100644
--- a/docs/about/emulation.rst
+++ b/docs/about/emulation.rst
@@ -268,6 +268,36 @@ Behaviour can be tweaked with the following arguments:
   * - idle=true|false
     - Dump the current execution stats whenever the guest vCPU idles
 
+Basic Block Vectors
+...................
+
+``contrib/plugins/bbv.c``
+
+The bbv plugin allows you to generate basic block vectors for use with the
+`SimPoint <https://cseweb.ucsd.edu/~calder/simpoint/>`__ analysis tool.
+
+.. list-table:: Basic block vectors arguments
+  :widths: 20 80
+  :header-rows: 1
+
+  * - Option
+    - Description
+  * - interval=N
+    - The interval to generate a basic block vector specified by the number of
+      instructions (Default: N = 100000000)
+  * - outfile=PATH
+    - The path to output files.
+      It will be suffixed with ``.N.bb`` where ``N`` is a vCPU index.
+
+Example::
+
+  $ qemu-aarch64 \
+    -plugin contrib/plugins/libbbv.so,interval=100,outfile=sha1 \
+    tests/tcg/aarch64-linux-user/sha1
+  SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
+  $ du sha1.0.bb
+  23128   sha1.0.bb
+
 Instruction
 ...........