DWARF parsing and writing support using LLVM (#2520)

This imports LLVM code for DWARF handling. That code has the
Apache 2 license like us. It's also the same code used to
emit DWARF in the common toolchain, so it seems like a safe choice.

This adds two passes: --dwarfdump which runs the same code LLVM
runs for llvm-dwarfdump. This shows we can parse it ok, and will
be useful for debugging. And --dwarfupdate writes out the DWARF
sections (unchanged from what we read, so it just roundtrips - for
updating we need #2515).

This puts LLVM in thirdparty which is added here.

All the LLVM code is behind USE_LLVM_DWARF, which is on
by default, but off in JS for now, as it increases code size by 20%.

This current approach imports the LLVM files directly. This is not
how they are intended to be used, so it required a bunch of
local changes - more than I expected actually, for the platform-specific
stuff. For now this seems to work, so it may be good enough, but
in the long term we may want to switch to linking against libllvm.
A downside to doing that is that binaryen users would need to
have an LLVM build, and even in the waterfall builds we'd have a
problem - while we ship LLVM there anyhow, we constantly update
it, which means that binaryen would need to be on latest llvm all
the time too (which otherwise, given DWARF is quite stable, we
might not need to constantly update).

An even larger issue is that as I did this work I learned about how
DWARF works in LLVM, and while the reading code is easy to
reuse, the writing code is trickier. The main code path is heavily
integrated with the MC layer, which we don't have - we might want
to create a "fake MC layer" for that, but it sounds hard. Instead,
there is the YAML path which is used mostly for testing, and which
can convert DWARF to and from YAML and from binary. Using
the non-YAML parts there, we can convert binary DWARF to
the YAML layer's nice Info data, then convert that to binary. This
works, however, this is not the path LLVM uses normally, and it
supports only some basic DWARF sections - I had to add ranges
support, in fact. So if we need more complex things, we may end
up needing to use the MC layer approach, or consider some other
DWARF library. However, hopefully that should not affect the core
binaryen code which just calls a library for DWARF stuff.

Helps #2400

1 files changed, 157 insertions, 0 deletions

diff --git a/third_party/llvm-project/Debug.cpp b/third_party/llvm-project/Debug.cpp
new file mode 100644
index 000000000..9d90546a6
--- /dev/null
+++ b/third_party/llvm-project/Debug.cpp
@@ -0,0 +1,157 @@
+//===-- Debug.cpp - An easy way to add debug output to your code ----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a handy way of adding debugging information to your
+// code, without it being enabled all of the time, and without having to add
+// command line options to enable it.
+//
+// In particular, just wrap your code with the LLVM_DEBUG() macro, and it will
+// be enabled automatically if you specify '-debug' on the command-line.
+// Alternatively, you can also use the SET_DEBUG_TYPE("foo") macro to specify
+// that your debug code belongs to class "foo".  Then, on the command line, you
+// can specify '-debug-only=foo' to enable JUST the debug information for the
+// foo class.
+//
+// When compiling without assertions, the -debug-* options and all code in
+// LLVM_DEBUG() statements disappears, so it does not affect the runtime of the
+// code.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/Signals.h"
+#include "llvm/Support/circular_raw_ostream.h"
+#include "llvm/Support/raw_ostream.h"
+
+#undef isCurrentDebugType
+#undef setCurrentDebugType
+#undef setCurrentDebugTypes
+
+using namespace llvm;
+
+// Even though LLVM might be built with NDEBUG, define symbols that the code
+// built without NDEBUG can depend on via the llvm/Support/Debug.h header.
+namespace llvm {
+/// Exported boolean set by the -debug option.
+bool DebugFlag = false;
+
+#if 0 // XXX BINARYEN
+static ManagedStatic<std::vector<std::string>> CurrentDebugType;
+#endif
+
+/// Return true if the specified string is the debug type
+/// specified on the command line, or if none was specified on the command line
+/// with the -debug-only=X option.
+bool isCurrentDebugType(const char *DebugType) {
+  llvm_unreachable("debug type");
+}
+
+/// Set the current debug type, as if the -debug-only=X
+/// option were specified.  Note that DebugFlag also needs to be set to true for
+/// debug output to be produced.
+///
+void setCurrentDebugTypes(const char **Types, unsigned Count);
+
+void setCurrentDebugType(const char *Type) {
+  setCurrentDebugTypes(&Type, 1);
+}
+
+void setCurrentDebugTypes(const char **Types, unsigned Count) {
+  llvm_unreachable("set debug type");
+}
+} // namespace llvm
+
+// All Debug.h functionality is a no-op in NDEBUG mode.
+#if 0 // XXX BINARYEN ndef NDEBUG
+
+// -debug - Command line option to enable the DEBUG statements in the passes.
+// This flag may only be enabled in debug builds.
+static cl::opt<bool, true>
+Debug("debug", cl::desc("Enable debug output"), cl::Hidden,
+      cl::location(DebugFlag));
+
+// -debug-buffer-size - Buffer the last N characters of debug output
+//until program termination.
+static cl::opt<unsigned>
+DebugBufferSize("debug-buffer-size",
+                cl::desc("Buffer the last N characters of debug output "
+                         "until program termination. "
+                         "[default 0 -- immediate print-out]"),
+                cl::Hidden,
+                cl::init(0));
+
+namespace {
+
+struct DebugOnlyOpt {
+  void operator=(const std::string &Val) const {
+    if (Val.empty())
+      return;
+    DebugFlag = true;
+    SmallVector<StringRef,8> dbgTypes;
+    StringRef(Val).split(dbgTypes, ',', -1, false);
+    for (auto dbgType : dbgTypes)
+      CurrentDebugType->push_back(dbgType);
+  }
+};
+
+}
+
+static DebugOnlyOpt DebugOnlyOptLoc;
+
+static cl::opt<DebugOnlyOpt, true, cl::parser<std::string> >
+DebugOnly("debug-only", cl::desc("Enable a specific type of debug output (comma separated list of types)"),
+          cl::Hidden, cl::ZeroOrMore, cl::value_desc("debug string"),
+          cl::location(DebugOnlyOptLoc), cl::ValueRequired);
+// Signal handlers - dump debug output on termination.
+static void debug_user_sig_handler(void *Cookie) {
+  // This is a bit sneaky.  Since this is under #ifndef NDEBUG, we
+  // know that debug mode is enabled and dbgs() really is a
+  // circular_raw_ostream.  If NDEBUG is defined, then dbgs() ==
+  // errs() but this will never be invoked.
+  llvm::circular_raw_ostream &dbgout =
+      static_cast<circular_raw_ostream &>(llvm::dbgs());
+  dbgout.flushBufferWithBanner();
+}
+
+/// dbgs - Return a circular-buffered debug stream.
+raw_ostream &llvm::dbgs() {
+  // Do one-time initialization in a thread-safe way.
+  static struct dbgstream {
+    circular_raw_ostream strm;
+
+    dbgstream() :
+        strm(errs(), "*** Debug Log Output ***\n",
+             (!EnableDebugBuffering || !DebugFlag) ? 0 : DebugBufferSize) {
+      if (EnableDebugBuffering && DebugFlag && DebugBufferSize != 0)
+        // TODO: Add a handler for SIGUSER1-type signals so the user can
+        // force a debug dump.
+        sys::AddSignalHandler(&debug_user_sig_handler, nullptr);
+      // Otherwise we've already set the debug stream buffer size to
+      // zero, disabling buffering so it will output directly to errs().
+    }
+  } thestrm;
+
+  return thestrm.strm;
+}
+
+#else
+// Avoid "has no symbols" warning.
+namespace llvm {
+  /// dbgs - Return errs().
+  raw_ostream &dbgs() {
+    return errs();
+  }
+}
+
+#endif
+
+/// EnableDebugBuffering - Turn on signal handler installation.
+///
+bool llvm::EnableDebugBuffering = false;