[PULL 19/22] contrib/plugins: extend execlog to track register changes

["Alex Bennée" <alex.bennee@linaro.org>]

With the new plugin register API we can now track changes to register
values. Currently the implementation is fairly dumb which will slow
down if a large number of register values are being tracked. This
could be improved by only instrumenting instructions which mention
registers we are interested in tracking.

Example usage:

  ./qemu-aarch64 -D plugin.log -d plugin \
     -cpu max,sve256=on \
     -plugin contrib/plugins/libexeclog.so,reg=sp,reg=z\* \
     ./tests/tcg/aarch64-linux-user/sha512-sve

will display in the execlog any changes to the stack pointer (sp) and
the SVE Z registers.

Message-Id: <20240103173349.398526-41-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Akihiko Odaki <akihiko.odaki@daynix.com>
Based-On: <20231025093128.33116-19-akihiko.odaki@daynix.com>

diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
index 81dcd43a612..3a0962723d7 100644
--- a/docs/devel/tcg-plugins.rst
+++ b/docs/devel/tcg-plugins.rst
@@ -497,6 +497,14 @@ arguments if required::
   $ qemu-system-arm $(QEMU_ARGS) \
     -plugin ./contrib/plugins/libexeclog.so,ifilter=st1w,afilter=0x40001808 -d plugin
 
+This plugin can also dump registers when they change value. Specify the name of the
+registers with multiple ``reg`` options. You can also use glob style matching if you wish::
+
+  $ qemu-system-arm $(QEMU_ARGS) \
+    -plugin ./contrib/plugins/libexeclog.so,reg=\*_el2,reg=sp -d plugin
+
+Be aware that each additional register to check will slow down execution quite considerably.
+
 - contrib/plugins/cache.c
 
 Cache modelling plugin that measures the performance of a given L1 cache
@@ -583,4 +591,3 @@ The following API is generated from the inline documentation in
 include the full kernel-doc annotations.
 
 .. kernel-doc:: include/qemu/qemu-plugin.h
-
diff --git a/contrib/plugins/execlog.c b/contrib/plugins/execlog.c
index f262e5555eb..c20e88a6941 100644
--- a/contrib/plugins/execlog.c
+++ b/contrib/plugins/execlog.c
@@ -1,7 +1,7 @@
 /*
  * Copyright (C) 2021, Alexandre Iooss <erdnaxe@crans.org>
  *
- * Log instruction execution with memory access.
+ * Log instruction execution with memory access and register changes
  *
  * License: GNU GPL, version 2 or later.
  *   See the COPYING file in the top-level directory.
@@ -15,30 +15,29 @@
 
 #include <qemu-plugin.h>
 
+typedef struct {
+    struct qemu_plugin_register *handle;
+    GByteArray *last;
+    GByteArray *new;
+    const char *name;
+} Register;
+
+typedef struct CPU {
+    /* Store last executed instruction on each vCPU as a GString */
+    GString *last_exec;
+    /* Ptr array of Register */
+    GPtrArray *registers;
+} CPU;
+
 QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
 
-/* Store last executed instruction on each vCPU as a GString */
-static GPtrArray *last_exec;
+static CPU *cpus;
+static int num_cpus;
 static GRWLock expand_array_lock;
 
 static GPtrArray *imatches;
 static GArray *amatches;
-
-/*
- * Expand last_exec array.
- *
- * As we could have multiple threads trying to do this we need to
- * serialise the expansion under a lock.
- */
-static void expand_last_exec(int cpu_index)
-{
-    g_rw_lock_writer_lock(&expand_array_lock);
-    while (cpu_index >= last_exec->len) {
-        GString *s = g_string_new(NULL);
-        g_ptr_array_add(last_exec, s);
-    }
-    g_rw_lock_writer_unlock(&expand_array_lock);
-}
+static GPtrArray *rmatches;
 
 /**
  * Add memory read or write information to current instruction log
@@ -50,8 +49,8 @@ static void vcpu_mem(unsigned int cpu_index, qemu_plugin_meminfo_t info,
 
     /* Find vCPU in array */
     g_rw_lock_reader_lock(&expand_array_lock);
-    g_assert(cpu_index < last_exec->len);
-    s = g_ptr_array_index(last_exec, cpu_index);
+    g_assert(cpu_index < num_cpus);
+    s = cpus[cpu_index].last_exec;
     g_rw_lock_reader_unlock(&expand_array_lock);
 
     /* Indicate type of memory access */
@@ -77,28 +76,46 @@ static void vcpu_mem(unsigned int cpu_index, qemu_plugin_meminfo_t info,
  */
 static void vcpu_insn_exec(unsigned int cpu_index, void *udata)
 {
-    GString *s;
+    CPU *cpu;
 
-    /* Find or create vCPU in array */
     g_rw_lock_reader_lock(&expand_array_lock);
-    if (cpu_index >= last_exec->len) {
-        g_rw_lock_reader_unlock(&expand_array_lock);
-        expand_last_exec(cpu_index);
-        g_rw_lock_reader_lock(&expand_array_lock);
-    }
-    s = g_ptr_array_index(last_exec, cpu_index);
+    g_assert(cpu_index < num_cpus);
+    cpu = &cpus[cpu_index];
     g_rw_lock_reader_unlock(&expand_array_lock);
 
     /* Print previous instruction in cache */
-    if (s->len) {
-        qemu_plugin_outs(s->str);
+    if (cpu->last_exec->len) {
+        if (cpu->registers) {
+            for (int n = 0; n < cpu->registers->len; n++) {
+                Register *reg = cpu->registers->pdata[n];
+                int sz;
+
+                g_byte_array_set_size(reg->new, 0);
+                sz = qemu_plugin_read_register(cpu_index, reg->handle, reg->new);
+                g_assert(sz == reg->last->len);
+
+                if (memcmp(reg->last->data, reg->new->data, sz)) {
+                    GByteArray *temp = reg->last;
+                    g_string_append_printf(cpu->last_exec, ", %s -> 0x", reg->name);
+                    /* TODO: handle BE properly */
+                    for (int i = sz; i >= 0; i--) {
+                        g_string_append_printf(cpu->last_exec, "%02x",
+                                               reg->new->data[i]);
+                    }
+                    reg->last = reg->new;
+                    reg->new = temp;
+                }
+            }
+        }
+
+        qemu_plugin_outs(cpu->last_exec->str);
         qemu_plugin_outs("\n");
     }
 
     /* Store new instruction in cache */
     /* vcpu_mem will add memory access information to last_exec */
-    g_string_printf(s, "%u, ", cpu_index);
-    g_string_append(s, (char *)udata);
+    g_string_printf(cpus[cpu_index].last_exec, "%u, ", cpu_index);
+    g_string_append(cpus[cpu_index].last_exec, (char *)udata);
 }
 
 /**
@@ -167,8 +184,10 @@ static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
                                              QEMU_PLUGIN_MEM_RW, NULL);
 
             /* Register callback on instruction */
-            qemu_plugin_register_vcpu_insn_exec_cb(insn, vcpu_insn_exec,
-                                                   QEMU_PLUGIN_CB_NO_REGS, output);
+            qemu_plugin_register_vcpu_insn_exec_cb(
+                insn, vcpu_insn_exec,
+                rmatches ? QEMU_PLUGIN_CB_R_REGS : QEMU_PLUGIN_CB_NO_REGS,
+                output);
 
             /* reset skip */
             skip = (imatches || amatches);
@@ -177,17 +196,86 @@ static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
     }
 }
 
+static Register *init_vcpu_register(int vcpu_index,
+                                    qemu_plugin_reg_descriptor *desc)
+{
+    Register *reg = g_new0(Register, 1);
+    int r;
+
+    reg->handle = desc->handle;
+    reg->name = g_strdup(desc->name);
+    reg->last = g_byte_array_new();
+    reg->new = g_byte_array_new();
+
+    /* read the initial value */
+    r = qemu_plugin_read_register(vcpu_index, reg->handle, reg->last);
+    g_assert(r > 0);
+    return reg;
+}
+
+static registers_init(int vcpu_index)
+{
+    GPtrArray *registers = g_ptr_array_new();
+    g_autoptr(GArray) reg_list = qemu_plugin_get_registers(vcpu_index);
+
+    if (reg_list && reg_list->len) {
+        /*
+         * Go through each register in the complete list and
+         * see if we want to track it.
+         */
+        for (int r = 0; r < reg_list->len; r++) {
+            qemu_plugin_reg_descriptor *rd = &g_array_index(
+                reg_list, qemu_plugin_reg_descriptor, r);
+            for (int p = 0; p < rmatches->len; p++) {
+                g_autoptr(GPatternSpec) pat = g_pattern_spec_new(rmatches->pdata[p]);
+                if (g_pattern_match_string(pat, rd->name)) {
+                    Register *reg = init_vcpu_register(vcpu_index, rd);
+                    g_ptr_array_add(registers, reg);
+                }
+            }
+        }
+    }
+    cpus[num_cpus].registers = registers;
+}
+
+/*
+ * Initialise a new vcpu/thread with:
+ *   - last_exec tracking data
+ *   - list of tracked registers
+ *   - initial value of registers
+ *
+ * As we could have multiple threads trying to do this we need to
+ * serialise the expansion under a lock.
+ */
+static void vcpu_init(qemu_plugin_id_t id, unsigned int vcpu_index)
+{
+    g_rw_lock_writer_lock(&expand_array_lock);
+
+    if (vcpu_index >= num_cpus) {
+        cpus = g_realloc_n(cpus, vcpu_index + 1, sizeof(*cpus));
+        while (vcpu_index >= num_cpus) {
+            cpus[num_cpus].last_exec = g_string_new(NULL);
+
+            /* Any registers to track? */
+            if (rmatches && rmatches->len) {
+                registers_init(vcpu_index);
+            }
+            num_cpus++;
+        }
+    }
+
+    g_rw_lock_writer_unlock(&expand_array_lock);
+}
+
 /**
  * On plugin exit, print last instruction in cache
  */
 static void plugin_exit(qemu_plugin_id_t id, void *p)
 {
     guint i;
-    GString *s;
-    for (i = 0; i < last_exec->len; i++) {
-        s = g_ptr_array_index(last_exec, i);
-        if (s->str) {
-            qemu_plugin_outs(s->str);
+    for (i = 0; i < num_cpus; i++) {
+        if (cpus[i].last_exec->str) {
+            qemu_plugin_outs(cpus[i].last_exec->str);
             qemu_plugin_outs("\n");
         }
     }
@@ -212,6 +300,18 @@ static void parse_vaddr_match(char *match)
     g_array_append_val(amatches, v);
 }
 
+/*
+ * We have to wait until vCPUs are started before we can check the
+ * patterns find anything.
+ */
+static void add_regpat(char *regpat)
+{
+    if (!rmatches) {
+        rmatches = g_ptr_array_new();
+    }
+    g_ptr_array_add(rmatches, g_strdup(regpat));
+}
+
 /**
  * Install the plugin
  */
@@ -224,9 +324,7 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
      * we don't know the size before emulation.
      */
     if (info->system_emulation) {
-        last_exec = g_ptr_array_sized_new(info->system.max_vcpus);
-    } else {
-        last_exec = g_ptr_array_new();
+        cpus = g_new(CPU, info->system.max_vcpus);
     }
 
     for (int i = 0; i < argc; i++) {
@@ -236,13 +334,16 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
             parse_insn_match(tokens[1]);
         } else if (g_strcmp0(tokens[0], "afilter") == 0) {
             parse_vaddr_match(tokens[1]);
+        } else if (g_strcmp0(tokens[0], "reg") == 0) {
+            add_regpat(tokens[1]);
         } else {
             fprintf(stderr, "option parsing failed: %s\n", opt);
             return -1;
         }
     }
 
-    /* Register translation block and exit callbacks */
+    /* Register init, translation block and exit callbacks */
+    qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
     qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
     qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
 
-- 
2.39.2