9 files changed, 216 insertions, 15 deletions
diff --git a/absl/debugging/BUILD.bazel b/absl/debugging/BUILD.bazel
index 2aac0f66..a8c51a5c 100644
--- a/absl/debugging/BUILD.bazel
+++ b/absl/debugging/BUILD.bazel
@@ -34,6 +34,7 @@ cc_library(
         "internal/stacktrace_aarch64-inl.inc",
         "internal/stacktrace_arm-inl.inc",
         "internal/stacktrace_config.h",
+        "internal/stacktrace_emscripten-inl.inc",
         "internal/stacktrace_generic-inl.inc",
         "internal/stacktrace_powerpc-inl.inc",
         "internal/stacktrace_unimplemented-inl.inc",
@@ -57,6 +58,7 @@ cc_library(
         "symbolize.cc",
         "symbolize_darwin.inc",
         "symbolize_elf.inc",
+        "symbolize_emscripten.inc",
         "symbolize_unimplemented.inc",
         "symbolize_win32.inc",
     ],
diff --git a/absl/debugging/CMakeLists.txt b/absl/debugging/CMakeLists.txt
index bb4d4c92..760772f3 100644
--- a/absl/debugging/CMakeLists.txt
+++ b/absl/debugging/CMakeLists.txt
@@ -22,6 +22,7 @@ absl_cc_library(
     "internal/stacktrace_aarch64-inl.inc"
     "internal/stacktrace_arm-inl.inc"
     "internal/stacktrace_config.h"
+    "internal/stacktrace_emscripten-inl.inc"
     "internal/stacktrace_generic-inl.inc"
     "internal/stacktrace_powerpc-inl.inc"
     "internal/stacktrace_unimplemented-inl.inc"
@@ -48,6 +49,7 @@ absl_cc_library(
     "symbolize.cc"
     "symbolize_darwin.inc"
     "symbolize_elf.inc"
+    "symbolize_emscripten.inc"
     "symbolize_unimplemented.inc"
     "symbolize_win32.inc"
   COPTS
diff --git a/absl/debugging/internal/stacktrace_config.h b/absl/debugging/internal/stacktrace_config.h
index cca410d4..6cceef26 100644
--- a/absl/debugging/internal/stacktrace_config.h
+++ b/absl/debugging/internal/stacktrace_config.h
@@ -37,6 +37,10 @@
   "absl/debugging/internal/stacktrace_generic-inl.inc"
 #endif
 
+#elif defined(__EMSCRIPTEN__)
+#define ABSL_STACKTRACE_INL_HEADER \
+  "absl/debugging/internal/stacktrace_emscripten-inl.inc"
+
 #elif defined(__linux__) && !defined(__ANDROID__)
 
 #if defined(NO_FRAME_POINTER) && \
@@ -68,7 +72,6 @@
   "absl/debugging/internal/stacktrace_generic-inl.inc"
 #endif
 #endif
-
 #endif
 
 // Fallback to the empty implementation.
diff --git a/absl/debugging/internal/stacktrace_emscripten-inl.inc b/absl/debugging/internal/stacktrace_emscripten-inl.inc
new file mode 100644
index 00000000..0f444514
--- /dev/null
+++ b/absl/debugging/internal/stacktrace_emscripten-inl.inc
@@ -0,0 +1,110 @@
+// Copyright 2017 The Abseil Authors.
+//
+// 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
+//
+//      https://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.
+//
+// Portable implementation - just use glibc
+//
+// Note:  The glibc implementation may cause a call to malloc.
+// This can cause a deadlock in HeapProfiler.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_EMSCRIPTEN_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_EMSCRIPTEN_INL_H_
+
+#include <emscripten.h>
+
+#include <atomic>
+#include <cstring>
+
+#include "absl/base/attributes.h"
+#include "absl/debugging/stacktrace.h"
+
+extern "C" {
+uintptr_t emscripten_stack_snapshot();
+uint32_t emscripten_stack_unwind_buffer(uintptr_t pc, void *buffer,
+                                        uint32_t depth);
+}
+
+// Sometimes, we can try to get a stack trace from within a stack
+// trace, which can cause a self-deadlock.
+// Protect against such reentrant call by failing to get a stack trace.
+//
+// We use __thread here because the code here is extremely low level -- it is
+// called while collecting stack traces from within malloc and mmap, and thus
+// can not call anything which might call malloc or mmap itself.
+static __thread int recursive = 0;
+
+// The stack trace function might be invoked very early in the program's
+// execution (e.g. from the very first malloc).
+// As such, we suppress usage of backtrace during this early stage of execution.
+static std::atomic<bool> disable_stacktraces(true);  // Disabled until healthy.
+// Waiting until static initializers run seems to be late enough.
+// This file is included into stacktrace.cc so this will only run once.
+ABSL_ATTRIBUTE_UNUSED static int stacktraces_enabler = []() {
+  // Check if we can even create stacktraces. If not, bail early and leave
+  // disable_stacktraces set as-is.
+  // clang-format off
+  if (!EM_ASM_INT({ return (typeof wasmOffsetConverter !== 'undefined'); })) {
+    return 0;
+  }
+  // clang-format on
+  disable_stacktraces.store(false, std::memory_order_relaxed);
+  return 0;
+}();
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
+                      const void *ucp, int *min_dropped_frames) {
+  if (recursive || disable_stacktraces.load(std::memory_order_relaxed)) {
+    return 0;
+  }
+  ++recursive;
+
+  static_cast<void>(ucp);  // Unused.
+  constexpr int kStackLength = 64;
+  void *stack[kStackLength];
+
+  int size;
+  uintptr_t pc = emscripten_stack_snapshot();
+  size = emscripten_stack_unwind_buffer(pc, stack, kStackLength);
+
+  int result_count = size - skip_count;
+  if (result_count < 0) result_count = 0;
+  if (result_count > max_depth) result_count = max_depth;
+  for (int i = 0; i < result_count; i++) result[i] = stack[i + skip_count];
+
+  if (IS_STACK_FRAMES) {
+    // No implementation for finding out the stack frame sizes yet.
+    memset(sizes, 0, sizeof(*sizes) * result_count);
+  }
+  if (min_dropped_frames != nullptr) {
+    if (size - skip_count - max_depth > 0) {
+      *min_dropped_frames = size - skip_count - max_depth;
+    } else {
+      *min_dropped_frames = 0;
+    }
+  }
+
+  --recursive;
+
+  return result_count;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() { return true; }
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_EMSCRIPTEN_INL_H_
diff --git a/absl/debugging/internal/symbolize.h b/absl/debugging/internal/symbolize.h
index 4f26130f..8c296f89 100644
--- a/absl/debugging/internal/symbolize.h
+++ b/absl/debugging/internal/symbolize.h
@@ -68,6 +68,12 @@ ABSL_NAMESPACE_END
 #define ABSL_INTERNAL_HAVE_DARWIN_SYMBOLIZE 1
 #endif
 
+#ifdef ABSL_INTERNAL_HAVE_EMSCRIPTEN_SYMBOLIZE
+#error ABSL_INTERNAL_HAVE_EMSCRIPTEN_SYMBOLIZE cannot be directly set
+#elif defined(__EMSCRIPTEN__)
+#define ABSL_INTERNAL_HAVE_EMSCRIPTEN_SYMBOLIZE 1
+#endif
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
diff --git a/absl/debugging/stacktrace.cc b/absl/debugging/stacktrace.cc
index 1f7c7d82..5358b942 100644
--- a/absl/debugging/stacktrace.cc
+++ b/absl/debugging/stacktrace.cc
@@ -49,6 +49,7 @@
 
 # include "absl/debugging/internal/stacktrace_aarch64-inl.inc"
 # include "absl/debugging/internal/stacktrace_arm-inl.inc"
+# include "absl/debugging/internal/stacktrace_emscripten-inl.inc"
 # include "absl/debugging/internal/stacktrace_generic-inl.inc"
 # include "absl/debugging/internal/stacktrace_powerpc-inl.inc"
 # include "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
diff --git a/absl/debugging/symbolize.cc b/absl/debugging/symbolize.cc
index 5e4a25d6..f1abdfda 100644
--- a/absl/debugging/symbolize.cc
+++ b/absl/debugging/symbolize.cc
@@ -31,6 +31,8 @@
 #include "absl/debugging/symbolize_win32.inc"
 #elif defined(__APPLE__)
 #include "absl/debugging/symbolize_darwin.inc"
+#elif defined(__EMSCRIPTEN__)
+#include "absl/debugging/symbolize_emscripten.inc"
 #else
 #include "absl/debugging/symbolize_unimplemented.inc"
 #endif
diff --git a/absl/debugging/symbolize_emscripten.inc b/absl/debugging/symbolize_emscripten.inc
new file mode 100644
index 00000000..c226c456
--- /dev/null
+++ b/absl/debugging/symbolize_emscripten.inc
@@ -0,0 +1,72 @@
+// Copyright 2020 The Abseil Authors.
+//
+// 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
+//
+//      https://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 <cxxabi.h>
+#include <emscripten.h>
+
+#include <algorithm>
+#include <cstring>
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/debugging/internal/demangle.h"
+#include "absl/strings/numbers.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+
+extern "C" {
+const char* emscripten_pc_get_function(const void* pc);
+}
+
+// clang-format off
+EM_JS(bool, HaveOffsetConverter, (),
+      { return typeof wasmOffsetConverter !== 'undefined'; });
+// clang-format on
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+void InitializeSymbolizer(const char*) {
+  if (!HaveOffsetConverter()) {
+    ABSL_RAW_LOG(INFO,
+                 "Symbolization unavailable. Rebuild with -sWASM=1 "
+                 "and -sUSE_OFFSET_CONVERTER=1.");
+  }
+}
+
+bool Symbolize(const void* pc, char* out, int out_size) {
+  // Check if we have the offset converter necessary for pc_get_function.
+  // Without it, the program will abort().
+  if (!HaveOffsetConverter()) {
+    return false;
+  }
+  const char* func_name = emscripten_pc_get_function(pc);
+  if (func_name == nullptr) {
+    return false;
+  }
+
+  strncpy(out, func_name, out_size);
+
+  if (out[out_size - 1] != '\0') {
+    // strncpy() does not '\0' terminate when it truncates.
+    static constexpr char kEllipsis[] = "...";
+    int ellipsis_size = std::min<int>(sizeof(kEllipsis) - 1, out_size - 1);
+    memcpy(out + out_size - ellipsis_size - 1, kEllipsis, ellipsis_size);
+    out[out_size - 1] = '\0';
+  }
+
+  return true;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/absl/debugging/symbolize_test.cc b/absl/debugging/symbolize_test.cc
index 35de02e2..c710a3da 100644
--- a/absl/debugging/symbolize_test.cc
+++ b/absl/debugging/symbolize_test.cc
@@ -146,8 +146,22 @@ static const char *TrySymbolize(void *pc) {
   return TrySymbolizeWithLimit(pc, sizeof(try_symbolize_buffer));
 }
 
-#if defined(ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE) || \
-    defined(ABSL_INTERNAL_HAVE_DARWIN_SYMBOLIZE)
+#if defined(ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE) ||    \
+    defined(ABSL_INTERNAL_HAVE_DARWIN_SYMBOLIZE) || \
+    defined(ABSL_INTERNAL_HAVE_EMSCRIPTEN_SYMBOLIZE)
+
+// Test with a return address.
+void ABSL_ATTRIBUTE_NOINLINE TestWithReturnAddress() {
+#if defined(ABSL_HAVE_ATTRIBUTE_NOINLINE)
+  void *return_address = __builtin_return_address(0);
+  const char *symbol = TrySymbolize(return_address);
+  ABSL_RAW_CHECK(symbol != nullptr, "TestWithReturnAddress failed");
+  ABSL_RAW_CHECK(strcmp(symbol, "main") == 0, "TestWithReturnAddress failed");
+  std::cout << "TestWithReturnAddress passed" << std::endl;
+#endif
+}
+
+#ifndef ABSL_INTERNAL_HAVE_EMSCRIPTEN_SYMBOLIZE
 
 TEST(Symbolize, Cached) {
   // Compilers should give us pointers to them.
@@ -418,6 +432,7 @@ TEST(Symbolize, ForEachSection) {
   close(fd);
 }
 #endif  // !ABSL_INTERNAL_HAVE_DARWIN_SYMBOLIZE
+#endif  // !ABSL_INTERNAL_HAVE_EMSCRIPTEN_SYMBOLIZE
 
 // x86 specific tests.  Uses some inline assembler.
 extern "C" {
@@ -466,17 +481,6 @@ void ABSL_ATTRIBUTE_NOINLINE TestWithPCInsideInlineFunction() {
 }
 }
 
-// Test with a return address.
-void ABSL_ATTRIBUTE_NOINLINE TestWithReturnAddress() {
-#if defined(ABSL_HAVE_ATTRIBUTE_NOINLINE)
-  void *return_address = __builtin_return_address(0);
-  const char *symbol = TrySymbolize(return_address);
-  ABSL_RAW_CHECK(symbol != nullptr, "TestWithReturnAddress failed");
-  ABSL_RAW_CHECK(strcmp(symbol, "main") == 0, "TestWithReturnAddress failed");
-  std::cout << "TestWithReturnAddress passed" << std::endl;
-#endif
-}
-
 #if defined(__arm__) && ABSL_HAVE_ATTRIBUTE(target)
 // Test that we correctly identify bounds of Thumb functions on ARM.
 //
@@ -559,7 +563,6 @@ TEST(Symbolize, SymbolizeWithDemangling) {
 
 #endif  // !defined(ABSL_CONSUME_DLL)
 #else  // Symbolizer unimplemented
-
 TEST(Symbolize, Unimplemented) {
   char buf[64];
   EXPECT_FALSE(absl::Symbolize((void *)(&nonstatic_func), buf, sizeof(buf)));