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, 90 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/Signals.h b/third_party/llvm-project/include/llvm/Support/Signals.h
new file mode 100644
index 000000000..a6b215a24
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/Signals.h
@@ -0,0 +1,90 @@
+//===- llvm/Support/Signals.h - Signal Handling support ----------*- C++ -*-===//
+//
+// 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 defines some helpful functions for dealing with the possibility of
+// unix signals occurring while your program is running.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_SIGNALS_H
+#define LLVM_SUPPORT_SIGNALS_H
+
+#include <string>
+
+namespace llvm {
+class StringRef;
+class raw_ostream;
+
+namespace sys {
+
+  /// This function runs all the registered interrupt handlers, including the
+  /// removal of files registered by RemoveFileOnSignal.
+  void RunInterruptHandlers();
+
+  /// This function registers signal handlers to ensure that if a signal gets
+  /// delivered that the named file is removed.
+  /// Remove a file if a fatal signal occurs.
+  bool RemoveFileOnSignal(StringRef Filename, std::string* ErrMsg = nullptr);
+
+  /// This function removes a file from the list of files to be removed on
+  /// signal delivery.
+  void DontRemoveFileOnSignal(StringRef Filename);
+
+  /// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the
+  /// process, print a stack trace and then exit.
+  /// Print a stack trace if a fatal signal occurs.
+  /// \param Argv0 the current binary name, used to find the symbolizer
+  ///        relative to the current binary before searching $PATH; can be
+  ///        StringRef(), in which case we will only search $PATH.
+  /// \param DisableCrashReporting if \c true, disable the normal crash
+  ///        reporting mechanisms on the underlying operating system.
+  void PrintStackTraceOnErrorSignal(StringRef Argv0,
+                                    bool DisableCrashReporting = false);
+
+  /// Disable all system dialog boxes that appear when the process crashes.
+  void DisableSystemDialogsOnCrash();
+
+  /// Print the stack trace using the given \c raw_ostream object.
+  void PrintStackTrace(raw_ostream &OS);
+
+  // Run all registered signal handlers.
+  void RunSignalHandlers();
+
+  using SignalHandlerCallback = void (*)(void *);
+
+  /// Add a function to be called when an abort/kill signal is delivered to the
+  /// process. The handler can have a cookie passed to it to identify what
+  /// instance of the handler it is.
+  void AddSignalHandler(SignalHandlerCallback FnPtr, void *Cookie);
+
+  /// This function registers a function to be called when the user "interrupts"
+  /// the program (typically by pressing ctrl-c).  When the user interrupts the
+  /// program, the specified interrupt function is called instead of the program
+  /// being killed, and the interrupt function automatically disabled.
+  ///
+  /// Note that interrupt functions are not allowed to call any non-reentrant
+  /// functions.  An null interrupt function pointer disables the current
+  /// installed function.  Note also that the handler may be executed on a
+  /// different thread on some platforms.
+  void SetInterruptFunction(void (*IF)());
+
+  /// Registers a function to be called when an "info" signal is delivered to
+  /// the process.
+  ///
+  /// On POSIX systems, this will be SIGUSR1; on systems that have it, SIGINFO
+  /// will also be used (typically ctrl-t).
+  ///
+  /// Note that signal handlers are not allowed to call any non-reentrant
+  /// functions.  An null function pointer disables the current installed
+  /// function.  Note also that the handler may be executed on a different
+  /// thread on some platforms.
+  void SetInfoSignalFunction(void (*Handler)());
+} // End sys namespace
+} // End llvm namespace
+
+#endif