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, 70 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/Host.h b/third_party/llvm-project/include/llvm/Support/Host.h
new file mode 100644
index 000000000..44f543c36
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/Host.h
@@ -0,0 +1,70 @@
+//===- llvm/Support/Host.h - Host machine characteristics --------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Methods for querying the nature of the host machine.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_HOST_H
+#define LLVM_SUPPORT_HOST_H
+
+#include "llvm/ADT/StringMap.h"
+
+#include <string>
+
+namespace llvm {
+namespace sys {
+
+  /// getDefaultTargetTriple() - Return the default target triple the compiler
+  /// has been configured to produce code for.
+  ///
+  /// The target triple is a string in the format of:
+  ///   CPU_TYPE-VENDOR-OPERATING_SYSTEM
+  /// or
+  ///   CPU_TYPE-VENDOR-KERNEL-OPERATING_SYSTEM
+  std::string getDefaultTargetTriple();
+
+  /// getProcessTriple() - Return an appropriate target triple for generating
+  /// code to be loaded into the current process, e.g. when using the JIT.
+  std::string getProcessTriple();
+
+  /// getHostCPUName - Get the LLVM name for the host CPU. The particular format
+  /// of the name is target dependent, and suitable for passing as -mcpu to the
+  /// target which matches the host.
+  ///
+  /// \return - The host CPU name, or empty if the CPU could not be determined.
+  StringRef getHostCPUName();
+
+  /// getHostCPUFeatures - Get the LLVM names for the host CPU features.
+  /// The particular format of the names are target dependent, and suitable for
+  /// passing as -mattr to the target which matches the host.
+  ///
+  /// \param Features - A string mapping feature names to either
+  /// true (if enabled) or false (if disabled). This routine makes no guarantees
+  /// about exactly which features may appear in this map, except that they are
+  /// all valid LLVM feature names.
+  ///
+  /// \return - True on success.
+  bool getHostCPUFeatures(StringMap<bool> &Features);
+
+  /// Get the number of physical cores (as opposed to logical cores returned
+  /// from thread::hardware_concurrency(), which includes hyperthreads).
+  /// Returns -1 if unknown for the current host system.
+  int getHostNumPhysicalCores();
+
+  namespace detail {
+  /// Helper functions to extract HostCPUName from /proc/cpuinfo on linux.
+  StringRef getHostCPUNameForPowerPC(StringRef ProcCpuinfoContent);
+  StringRef getHostCPUNameForARM(StringRef ProcCpuinfoContent);
+  StringRef getHostCPUNameForS390x(StringRef ProcCpuinfoContent);
+  StringRef getHostCPUNameForBPF();
+  }
+}
+}
+
+#endif