From 9ba0fdc2964f1c42d013d40e0b81c421c1e02d97 Mon Sep 17 00:00:00 2001
From: Maxim Kokryashkin <m.kokryashkin@tarantool.org>
Date: Mon, 4 Dec 2023 21:26:04 +0300
Subject: [PATCH] bisect

---
 CMakeLists.txt     |   2 +-
 src/CMakeLists.txt |   2 +-
 src/lj_sysprof.c   | 100 ++++++++++++++-------------------------------
 3 files changed, 33 insertions(+), 71 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2638467abe..9f9a21713d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -222,7 +222,7 @@ else()
       CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64"
     )
   )
-    AppendFlags(CMAKE_C_FLAGS -fno-omit-frame-pointer -fasynchronous-unwind-tables)
+    #AppendFlags(CMAKE_C_FLAGS -fno-omit-frame-pointer -fasynchronous-unwind-tables)
     if(ENABLE_BUNDLED_LUAJIT)
         AppendFlags(TARGET_C_FLAGS -DLUAJIT_EXTERNAL_SYSPROF_BACKTRACER)
     else()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index be7df569c2..bd8e21249d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -284,7 +284,7 @@ add_dependencies(core_shared buildvm_output)
 
 list(APPEND TARGET_LIBS m)
 
-if(NOT LUAJIT_DISABLE_SYSPROF)
+if(${LIBUNWIND_FOUND})
   list(APPEND TARGET_LIBS ${LIBUNWIND_LIBRARIES})
 endif()
 
diff --git a/src/lj_sysprof.c b/src/lj_sysprof.c
index b7b0b0608a..c6c20de289 100644
--- a/src/lj_sysprof.c
+++ b/src/lj_sysprof.c
@@ -26,17 +26,7 @@
 
 #include <pthread.h>
 #include <errno.h>
-
-#ifndef LUAJIT_EXTERNAL_SYSPROF_BACKTRACER
-/*
-** We only need local unwinding, then a special implementation
-** can be selected which may run much faster than the generic
-** implementation which supports both kinds of unwinding, local
-** and remote.
-*/
-#define UNW_LOCAL_ONLY
-#include <libunwind.h>
-#endif
+#include <execinfo.h>
 
 /*
 ** Number of profiler frames we need to omit during stack
@@ -95,56 +85,6 @@ static struct sysprof sysprof = {0};
 
 /* --- Stream ------------------------------------------------------------- */
 
-#ifndef LUAJIT_EXTERNAL_SYSPROF_BACKTRACER
-
-static ssize_t collect_stack(void **buffer, int size)
-{
-  int frame_no = 0;
-  unw_context_t unw_ctx;
-  unw_cursor_t unw_cur;
-
-  int rc = unw_getcontext(&unw_ctx);
-  if (rc != 0)
-    return -1;
-
-  rc = unw_init_local(&unw_cur, &unw_ctx);
-  if (rc != 0)
-    return -1;
-
-  for (; frame_no < size; ++frame_no) {
-    unw_word_t ip;
-    rc = unw_get_reg(&unw_cur, UNW_REG_IP, &ip);
-    if (rc != 0)
-      return -1;
-
-    buffer[frame_no] = (void *)ip;
-    rc = unw_step(&unw_cur);
-    if (rc <= 0)
-      break;
-  }
-  return frame_no;
-}
-
-static void default_backtrace_host(void *(writer)(int frame_no, void *addr))
-{
-  static void *backtrace_buf[SYSPROF_BACKTRACE_FRAME_MAX] = {};
-
-  struct sysprof *sp = &sysprof;
-  int max_depth = sp->opt.mode == LUAM_SYSPROF_LEAF
-                  ? SYSPROF_HANDLER_STACK_DEPTH + 1
-                  : SYSPROF_BACKTRACE_FRAME_MAX;
-  const int depth = collect_stack(backtrace_buf, max_depth);
-  int level;
-
-  lj_assertX(depth <= max_depth, "backtrace is too deep");
-  lj_assertX(depth != -1, "failed to collect backtrace");
-  for (level = SYSPROF_HANDLER_STACK_DEPTH; level < depth; ++level) {
-    if (!writer(level - SYSPROF_HANDLER_STACK_DEPTH + 1, backtrace_buf[level]))
-      return;
-  }
-}
-#endif
-
 static const uint8_t ljp_header[] = {'l', 'j', 'p', LJP_FORMAT_VERSION,
                                       0x0, 0x0, 0x0};
 
@@ -265,6 +205,24 @@ static void *stream_frame_host(int frame_no, void *addr)
   return addr;
 }
 
+static void default_backtrace_host(void *(writer)(int frame_no, void *addr))
+{
+  static void *backtrace_buf[SYSPROF_BACKTRACE_FRAME_MAX] = {};
+
+  struct sysprof *sp = &sysprof;
+  int max_depth = sp->opt.mode == LUAM_SYSPROF_LEAF
+                  ? SYSPROF_HANDLER_STACK_DEPTH + 1
+                  : SYSPROF_BACKTRACE_FRAME_MAX;
+  const int depth = backtrace(backtrace_buf, max_depth);
+  int level;
+
+  lj_assertX(depth <= max_depth, "depth of C stack is too big");
+  for (level = SYSPROF_HANDLER_STACK_DEPTH; level < depth; ++level) {
+    if (!writer(level - SYSPROF_HANDLER_STACK_DEPTH + 1, backtrace_buf[level]))
+      return;
+  }
+}
+
 static void stream_backtrace_host(struct sysprof *sp)
 {
   lj_assertX(sp->backtracer != NULL, "uninitialized sysprof backtracer");
@@ -469,16 +427,20 @@ int lj_sysprof_set_backtracer(luam_Sysprof_backtracer backtracer) {
 
   if (sp->state != SPS_IDLE)
     return PROFILE_ERRUSE;
-
-  if (backtracer == NULL)
-#ifndef LUAJIT_EXTERNAL_SYSPROF_BACKTRACER
+  if (backtracer == NULL) {
     sp->backtracer = default_backtrace_host;
-#else
-    return PROFILE_ERRUSE;
-#endif
-  else
+    /*
+    ** XXX: `backtrace` is not signal-safe, according to man,
+    ** because it is lazy loaded on the first call, which triggers
+    ** allocations. We need to call `backtrace` before starting profiling
+    ** to avoid lazy loading.
+    */
+    void *dummy = NULL;
+    backtrace(&dummy, 1);
+  }
+  else {
     sp->backtracer = backtracer;
-
+  }
   if (!is_unconfigured(sp)) {
     sp->state = SPS_IDLE;
   }