From: Tudor Bosman <tudorb@fb.com>
Date: Thu, 20 Jun 2013 21:15:17 +0000 (-0700)
Subject: Use libunwind instead of the heavyweight thing from libgcc
X-Git-Tag: v0.22.0~945
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b78098f785d00f9b37d43d958c5e9d0d74397d18;p=folly.git

Use libunwind instead of the heavyweight thing from libgcc

Test Plan: exception_tracer_test

Reviewed By: bmaurer@fb.com

FB internal diff: D858195
---

diff --git a/folly/experimental/exception_tracer/ExceptionTracerBenchmark.cpp b/folly/experimental/exception_tracer/ExceptionTracerBenchmark.cpp
new file mode 100644
index 00000000..95c99eb1
--- /dev/null
+++ b/folly/experimental/exception_tracer/ExceptionTracerBenchmark.cpp
@@ -0,0 +1,63 @@
+/*
+ * Copyright 2013 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdexcept>
+#include <thread>
+#include <vector>
+
+#include <gflags/gflags.h>
+#include <glog/logging.h>
+
+#include "folly/Benchmark.h"
+#include "folly/experimental/exception_tracer/ExceptionTracer.h"
+
+void recurse(int level) {
+  if (level == 0) {
+    throw std::runtime_error("");
+  }
+  recurse(level - 1);
+  folly::doNotOptimizeAway(0);  // prevent tail recursion
+}
+
+void loop(int iters) {
+  for (int i = 0; i < iters * 100; ++i) {
+    try {
+      recurse(100);
+    } catch (const std::exception& e) {
+      folly::exception_tracer::getCurrentExceptions();
+    }
+  }
+}
+
+BENCHMARK(ExceptionTracer, iters) {
+  std::vector<std::thread> threads;
+  constexpr size_t kNumThreads = 10;
+  threads.resize(10);
+  for (auto& t : threads) {
+    t = std::thread([iters] () { loop(iters); });
+  }
+  for (auto& t : threads) {
+    t.join();
+  }
+}
+
+int main(int argc, char* argv[]) {
+  google::ParseCommandLineFlags(&argc, &argv, true);
+  google::InitGoogleLogging(argv[0]);
+  folly::runBenchmarks();
+  return 0;
+}
+
diff --git a/folly/experimental/exception_tracer/StackTrace.c b/folly/experimental/exception_tracer/StackTrace.c
index a10fb1b9..7a3d5cef 100644
--- a/folly/experimental/exception_tracer/StackTrace.c
+++ b/folly/experimental/exception_tracer/StackTrace.c
@@ -18,8 +18,12 @@
 #include "folly/experimental/exception_tracer/StackTrace.h"
 
 #include <errno.h>
+#include <stdio.h>
 #include <stdlib.h>
-#include "unwind.h"
+
+#define UNW_LOCAL_ONLY 1
+
+#include <libunwind.h>
 
 struct Context {
   StackTrace* trace;
@@ -27,43 +31,69 @@ struct Context {
   size_t capacity;
 };
 
-static _Unwind_Reason_Code addIP(struct _Unwind_Context* ctx, void* varg) {
-  struct Context* arg = (struct Context*)varg;
+static int checkError(const char* name, int err) {
+  if (err < 0) {
+    fprintf(stderr, "libunwind error: %s %d\n", name, err);
+    return -EINVAL;
+  }
+  return 0;
+}
 
-  if (arg->skip) {
-    --arg->skip;
-    return _URC_NO_REASON;
+static int addIP(struct Context* ctx, unw_cursor_t* cursor) {
+  if (ctx->skip) {
+    --ctx->skip;
+    return 0;
   }
 
-  if (arg->trace->frameCount == arg->capacity) {
-    size_t newCapacity = (arg->capacity < 8 ? 8 : arg->capacity * 1.5);
+  unw_word_t ip;
+  int r = unw_get_reg(cursor, UNW_REG_IP, &ip);
+  int err = checkError("unw_get_reg", r);
+  if (err) return err;
+
+  if (ctx->trace->frameCount == ctx->capacity) {
+    size_t newCapacity = (ctx->capacity < 8 ? 8 : ctx->capacity * 1.5);
     uintptr_t* newBlock =
-      realloc(arg->trace->frameIPs, newCapacity * sizeof(uintptr_t));
+      realloc(ctx->trace->frameIPs, newCapacity * sizeof(uintptr_t));
     if (!newBlock) {
-      return _URC_FATAL_PHASE1_ERROR;
+      return -ENOMEM;
     }
-    arg->trace->frameIPs = newBlock;
-    arg->capacity = newCapacity;
+    ctx->trace->frameIPs = newBlock;
+    ctx->capacity = newCapacity;
   }
 
-  arg->trace->frameIPs[arg->trace->frameCount++] = _Unwind_GetIP(ctx);
-  return _URC_NO_REASON;  /* success */
+  ctx->trace->frameIPs[ctx->trace->frameCount++] = ip;
+  return 0;  /* success */
 }
 
 int getCurrentStackTrace(size_t skip, StackTrace* trace) {
   trace->frameIPs = NULL;
   trace->frameCount = 0;
+
   struct Context ctx;
   ctx.trace = trace;
   ctx.skip = skip;
   ctx.capacity = 0;
 
-  if (_Unwind_Backtrace(addIP, &ctx) == _URC_END_OF_STACK) {
-    return 0;
+  unw_context_t uctx;
+  int r = unw_getcontext(&uctx);
+  int err = checkError("unw_get_context", r);
+  if (err) return err;
+
+  unw_cursor_t cursor;
+  r = unw_init_local(&cursor, &uctx);
+  err = checkError("unw_init_local", r);
+  if (err) return err;
+
+  while ((r = unw_step(&cursor)) > 0) {
+    if ((err = addIP(&ctx, &cursor)) != 0) {
+      destroyStackTrace(trace);
+      return err;
+    }
   }
+  err = checkError("unw_step", r);
+  if (err) return err;
 
-  destroyStackTrace(trace);
-  return -ENOMEM;
+  return 0;
 }
 
 void destroyStackTrace(StackTrace* trace) {