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, 209 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/Process.h b/third_party/llvm-project/include/llvm/Support/Process.h
new file mode 100644
index 000000000..67e379125
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/Process.h
@@ -0,0 +1,209 @@
+//===- llvm/Support/Process.h -----------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// Provides a library for accessing information about this process and other
+/// processes on the operating system. Also provides means of spawning
+/// subprocess for commands. The design of this library is modeled after the
+/// proposed design of the Boost.Process library, and is design specifically to
+/// follow the style of standard libraries and potentially become a proposal
+/// for a standard library.
+///
+/// This file declares the llvm::sys::Process class which contains a collection
+/// of legacy static interfaces for extracting various information about the
+/// current process. The goal is to migrate users of this API over to the new
+/// interfaces.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_PROCESS_H
+#define LLVM_SUPPORT_PROCESS_H
+
+#include "llvm/ADT/Optional.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/Chrono.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/Error.h"
+#include <system_error>
+
+namespace llvm {
+template <typename T> class ArrayRef;
+class StringRef;
+
+namespace sys {
+
+
+/// A collection of legacy interfaces for querying information about the
+/// current executing process.
+class Process {
+public:
+  /// Get the process's page size.
+  /// This may fail if the underlying syscall returns an error. In most cases,
+  /// page size information is used for optimization, and this error can be
+  /// safely discarded by calling consumeError, and an estimated page size
+  /// substituted instead.
+  static Expected<unsigned> getPageSize();
+
+  /// Get the process's estimated page size.
+  /// This function always succeeds, but if the underlying syscall to determine
+  /// the page size fails then this will silently return an estimated page size.
+  /// The estimated page size is guaranteed to be a power of 2.
+  static unsigned getPageSizeEstimate() {
+    if (auto PageSize = getPageSize())
+      return *PageSize;
+    else {
+      consumeError(PageSize.takeError());
+      return 4096;
+    }
+  }
+
+  /// Return process memory usage.
+  /// This static function will return the total amount of memory allocated
+  /// by the process. This only counts the memory allocated via the malloc,
+  /// calloc and realloc functions and includes any "free" holes in the
+  /// allocated space.
+  static size_t GetMallocUsage();
+
+  /// This static function will set \p user_time to the amount of CPU time
+  /// spent in user (non-kernel) mode and \p sys_time to the amount of CPU
+  /// time spent in system (kernel) mode.  If the operating system does not
+  /// support collection of these metrics, a zero duration will be for both
+  /// values.
+  /// \param elapsed Returns the system_clock::now() giving current time
+  /// \param user_time Returns the current amount of user time for the process
+  /// \param sys_time Returns the current amount of system time for the process
+  static void GetTimeUsage(TimePoint<> &elapsed,
+                           std::chrono::nanoseconds &user_time,
+                           std::chrono::nanoseconds &sys_time);
+
+  /// This function makes the necessary calls to the operating system to
+  /// prevent core files or any other kind of large memory dumps that can
+  /// occur when a program fails.
+  /// Prevent core file generation.
+  static void PreventCoreFiles();
+
+  /// true if PreventCoreFiles has been called, false otherwise.
+  static bool AreCoreFilesPrevented();
+
+  // This function returns the environment variable \arg name's value as a UTF-8
+  // string. \arg Name is assumed to be in UTF-8 encoding too.
+  static Optional<std::string> GetEnv(StringRef name);
+
+  /// This function searches for an existing file in the list of directories
+  /// in a PATH like environment variable, and returns the first file found,
+  /// according to the order of the entries in the PATH like environment
+  /// variable.  If an ignore list is specified, then any folder which is in
+  /// the PATH like environment variable but is also in IgnoreList is not
+  /// considered.
+  static Optional<std::string> FindInEnvPath(StringRef EnvName,
+                                             StringRef FileName,
+                                             ArrayRef<std::string> IgnoreList);
+
+  static Optional<std::string> FindInEnvPath(StringRef EnvName,
+                                             StringRef FileName);
+
+  // This functions ensures that the standard file descriptors (input, output,
+  // and error) are properly mapped to a file descriptor before we use any of
+  // them.  This should only be called by standalone programs, library
+  // components should not call this.
+  static std::error_code FixupStandardFileDescriptors();
+
+  // This function safely closes a file descriptor.  It is not safe to retry
+  // close(2) when it returns with errno equivalent to EINTR; this is because
+  // *nixen cannot agree if the file descriptor is, in fact, closed when this
+  // occurs.
+  //
+  // N.B. Some operating systems, due to thread cancellation, cannot properly
+  // guarantee that it will or will not be closed one way or the other!
+  static std::error_code SafelyCloseFileDescriptor(int FD);
+
+  /// This function determines if the standard input is connected directly
+  /// to a user's input (keyboard probably), rather than coming from a file
+  /// or pipe.
+  static bool StandardInIsUserInput();
+
+  /// This function determines if the standard output is connected to a
+  /// "tty" or "console" window. That is, the output would be displayed to
+  /// the user rather than being put on a pipe or stored in a file.
+  static bool StandardOutIsDisplayed();
+
+  /// This function determines if the standard error is connected to a
+  /// "tty" or "console" window. That is, the output would be displayed to
+  /// the user rather than being put on a pipe or stored in a file.
+  static bool StandardErrIsDisplayed();
+
+  /// This function determines if the given file descriptor is connected to
+  /// a "tty" or "console" window. That is, the output would be displayed to
+  /// the user rather than being put on a pipe or stored in a file.
+  static bool FileDescriptorIsDisplayed(int fd);
+
+  /// This function determines if the given file descriptor is displayd and
+  /// supports colors.
+  static bool FileDescriptorHasColors(int fd);
+
+  /// This function determines the number of columns in the window
+  /// if standard output is connected to a "tty" or "console"
+  /// window. If standard output is not connected to a tty or
+  /// console, or if the number of columns cannot be determined,
+  /// this routine returns zero.
+  static unsigned StandardOutColumns();
+
+  /// This function determines the number of columns in the window
+  /// if standard error is connected to a "tty" or "console"
+  /// window. If standard error is not connected to a tty or
+  /// console, or if the number of columns cannot be determined,
+  /// this routine returns zero.
+  static unsigned StandardErrColumns();
+
+  /// This function determines whether the terminal connected to standard
+  /// output supports colors. If standard output is not connected to a
+  /// terminal, this function returns false.
+  static bool StandardOutHasColors();
+
+  /// This function determines whether the terminal connected to standard
+  /// error supports colors. If standard error is not connected to a
+  /// terminal, this function returns false.
+  static bool StandardErrHasColors();
+
+  /// Enables or disables whether ANSI escape sequences are used to output
+  /// colors. This only has an effect on Windows.
+  /// Note: Setting this option is not thread-safe and should only be done
+  /// during initialization.
+  static void UseANSIEscapeCodes(bool enable);
+
+  /// Whether changing colors requires the output to be flushed.
+  /// This is needed on systems that don't support escape sequences for
+  /// changing colors.
+  static bool ColorNeedsFlush();
+
+  /// This function returns the colorcode escape sequences.
+  /// If ColorNeedsFlush() is true then this function will change the colors
+  /// and return an empty escape sequence. In that case it is the
+  /// responsibility of the client to flush the output stream prior to
+  /// calling this function.
+  static const char *OutputColor(char c, bool bold, bool bg);
+
+  /// Same as OutputColor, but only enables the bold attribute.
+  static const char *OutputBold(bool bg);
+
+  /// This function returns the escape sequence to reverse forground and
+  /// background colors.
+  static const char *OutputReverse();
+
+  /// Resets the terminals colors, or returns an escape sequence to do so.
+  static const char *ResetColor();
+
+  /// Get the result of a process wide random number generator. The
+  /// generator will be automatically seeded in non-deterministic fashion.
+  static unsigned GetRandomNumber();
+};
+
+}
+}
+
+#endif