[PATCH 18/25] contrib/plugins/uftrace: define cpu operations and implement aarch64

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

From: Pierrick Bouvier <pierrick.bouvier@linaro.org>

We define a new CpuOps structure that will be used to implement tracking
independently of guest architecture.

As well, we now instrument only instructions following ones that might
have touched the frame pointer.

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-ID: <20250902075042.223990-3-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 contrib/plugins/uftrace.c | 114 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 110 insertions(+), 4 deletions(-)

diff --git a/contrib/plugins/uftrace.c b/contrib/plugins/uftrace.c
index 4af0130b159..d060513446c 100644
--- a/contrib/plugins/uftrace.c
+++ b/contrib/plugins/uftrace.c
@@ -11,14 +11,94 @@
 
 #include <qemu-plugin.h>
 #include <glib.h>
+#include <stdio.h>
 
 QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
 
+typedef struct Cpu Cpu;
+
+typedef struct {
+    void (*init)(Cpu *cpu);
+    void (*end)(Cpu *cpu);
+    uint64_t (*get_frame_pointer)(Cpu *cpu);
+    bool (*does_insn_modify_frame_pointer)(const char *disas);
+} CpuOps;
+
 typedef struct Cpu {
     GByteArray *buf;
+    CpuOps ops;
+    void *arch;
 } Cpu;
 
+typedef struct {
+    struct qemu_plugin_register *reg_fp;
+} Aarch64Cpu;
+
 static struct qemu_plugin_scoreboard *score;
+static CpuOps arch_ops;
+
+static uint64_t cpu_read_register64(Cpu *cpu, struct qemu_plugin_register *reg)
+{
+    GByteArray *buf = cpu->buf;
+    g_byte_array_set_size(buf, 0);
+    size_t sz = qemu_plugin_read_register(reg, buf);
+    g_assert(sz == 8);
+    g_assert(buf->len == 8);
+    return *((uint64_t *) buf->data);
+}
+
+static struct qemu_plugin_register *plugin_find_register(const char *name)
+{
+    g_autoptr(GArray) regs = qemu_plugin_get_registers();
+    for (int i = 0; i < regs->len; ++i) {
+        qemu_plugin_reg_descriptor *reg;
+        reg = &g_array_index(regs, qemu_plugin_reg_descriptor, i);
+        if (!strcmp(reg->name, name)) {
+            return reg->handle;
+        }
+    }
+    return NULL;
+}
+
+static uint64_t aarch64_get_frame_pointer(Cpu *cpu_)
+{
+    Aarch64Cpu *cpu = cpu_->arch;
+    return cpu_read_register64(cpu_, cpu->reg_fp);
+}
+
+static void aarch64_init(Cpu *cpu_)
+{
+    Aarch64Cpu *cpu = g_new0(Aarch64Cpu, 1);
+    cpu_->arch = cpu;
+    cpu->reg_fp = plugin_find_register("x29");
+    if (!cpu->reg_fp) {
+        fprintf(stderr, "uftrace plugin: frame pointer register (x29) is not "
+                        "available. Please use an AArch64 cpu (or -cpu max).\n");
+        g_abort();
+    }
+}
+
+static void aarch64_end(Cpu *cpu)
+{
+    g_free(cpu->arch);
+}
+
+static bool aarch64_does_insn_modify_frame_pointer(const char *disas)
+{
+    /*
+     * Check if current instruction concerns fp register "x29".
+     * We add a prefix space to make sure we don't match addresses dump
+     * in disassembly.
+     */
+    return strstr(disas, " x29");
+}
+
+static CpuOps aarch64_ops = {
+    .init = aarch64_init,
+    .end = aarch64_end,
+    .get_frame_pointer = aarch64_get_frame_pointer,
+    .does_insn_modify_frame_pointer = aarch64_does_insn_modify_frame_pointer,
+};
 
 static void track_callstack(unsigned int cpu_index, void *udata)
 {
@@ -28,19 +108,37 @@ static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
 {
     size_t n_insns = qemu_plugin_tb_n_insns(tb);
 
+    /*
+     * Callbacks and inline instrumentation are inserted before an instruction.
+     * Thus, to see instruction effect, we need to wait for next one.
+     * Potentially, the last instruction of a block could modify the frame
+     * pointer. Thus, we need to always instrument first instruction in a tb.
+     */
+    bool instrument_insn = true;
     for (size_t i = 0; i < n_insns; i++) {
         struct qemu_plugin_insn *insn = qemu_plugin_tb_get_insn(tb, i);
 
-        uintptr_t pc = qemu_plugin_insn_vaddr(insn);
-        qemu_plugin_register_vcpu_insn_exec_cb(insn, track_callstack,
-                                               QEMU_PLUGIN_CB_R_REGS,
-                                               (void *) pc);
+        if (instrument_insn) {
+            uintptr_t pc = qemu_plugin_insn_vaddr(insn);
+            qemu_plugin_register_vcpu_insn_exec_cb(insn, track_callstack,
+                                                   QEMU_PLUGIN_CB_R_REGS,
+                                                   (void *) pc);
+            instrument_insn = false;
+        }
+
+        char *disas = qemu_plugin_insn_disas(insn);
+        if (arch_ops.does_insn_modify_frame_pointer(disas)) {
+            instrument_insn = true;
+        }
     }
 }
 
 static void vcpu_init(qemu_plugin_id_t id, unsigned int vcpu_index)
 {
     Cpu *cpu = qemu_plugin_scoreboard_find(score, vcpu_index);
+    cpu->ops = arch_ops;
+
+    cpu->ops.init(cpu);
     cpu->buf = g_byte_array_new();
 }
 
@@ -64,6 +162,14 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
                                            const qemu_info_t *info,
                                            int argc, char **argv)
 {
+    if (!strcmp(info->target_name, "aarch64")) {
+        arch_ops = aarch64_ops;
+    } else {
+        fprintf(stderr, "plugin uftrace: %s target is not supported\n",
+                info->target_name);
+        return 1;
+    }
+
     score = qemu_plugin_scoreboard_new(sizeof(Cpu));
     qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
     qemu_plugin_register_atexit_cb(id, at_exit, NULL);
-- 
2.47.3