Move gdbsupport to the top level

This patch moves the gdbsupport directory to the top level.  This is
the next step in the ongoing project to move gdbserver to the top
level.

The bulk of this patch was created by "git mv gdb/gdbsupport gdbsupport".

This patch then adds a build system to gdbsupport and wires it into
the top level.  Then it changes gdb to use the top-level build.

gdbserver, on the other hand, is not yet changed.  It still does its
own build of gdbsupport.

ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* src-release.sh (GDB_SUPPORT_DIRS): Add gdbsupport.
	* MAINTAINERS: Add gdbsupport.
	* configure: Rebuild.
	* configure.ac (configdirs): Add gdbsupport.
	* gdbsupport: New directory, move from gdb/gdbsupport.
	* Makefile.def (host_modules, dependencies): Add gnulib.
	* Makefile.in: Rebuild.

gdb/ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* nat/x86-linux-dregs.c: Include configh.h.
	* nat/linux-ptrace.c: Include configh.h.
	* nat/linux-btrace.c: Include configh.h.
	* defs.h: Include config.h, bfd.h.
	* configure.ac: Don't source common.host.
	(CONFIG_OBS, CONFIG_SRCS): Remove gdbsupport files.
	* configure: Rebuild.
	* acinclude.m4: Update path.
	* Makefile.in (SUPPORT, LIBSUPPORT, INCSUPPORT): New variables.
	(CONFIG_SRC_SUBDIR): Remove gdbsupport.
	(INTERNAL_CFLAGS_BASE): Add INCSUPPORT.
	(CLIBS): Add LIBSUPPORT.
	(CDEPS): Likewise.
	(COMMON_SFILES): Remove gdbsupport files.
	(HFILES_NO_SRCDIR): Likewise.
	(stamp-version): Update path to create-version.sh.
	(ALLDEPFILES): Remove gdbsupport files.

gdb/gdbserver/ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* server.h: Include config.h.
	* gdbreplay.c: Include config.h.
	* configure: Rebuild.
	* configure.ac: Don't source common.host.
	* acinclude.m4: Update path.
	* Makefile.in (INCSUPPORT): New variable.
	(INCLUDE_CFLAGS): Add INCSUPPORT.
	(SFILES): Update paths.
	(version-generated.c): Update path to create-version.sh.
	(gdbsupport/%-ipa.o, gdbsupport/%.o): Update paths.

gdbsupport/ChangeLog
2020-01-14  Tom Tromey  <tom@tromey.com>

	* common-defs.h: Add GDBSERVER case.  Update includes.
	* acinclude.m4, aclocal.m4, config.in, configure, configure.ac,
	Makefile.am, Makefile.in, README: New files.
	* Moved from ../gdb/gdbsupport/

Change-Id: I07632e7798635c1bab389bf885971e584fb4bb78

1 files changed, 323 insertions, 0 deletions

diff --git a/gdbsupport/function-view.h b/gdbsupport/function-view.h
new file mode 100644
index 0000000..4e205b8
--- /dev/null
+++ b/gdbsupport/function-view.h
@@ -0,0 +1,323 @@
+/* Copyright (C) 2017-2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef COMMON_FUNCTION_VIEW_H
+#define COMMON_FUNCTION_VIEW_H
+
+/* function_view is a polymorphic type-erasing wrapper class that
+   encapsulates a non-owning reference to arbitrary callable objects.
+
+   A way to put it is that function_view is to std::function like
+   std::string_view is to std::string.  While std::function stores a
+   type-erased callable object internally, function_view holds a
+   type-erased reference to an external callable object.
+
+   This is meant to be used as callback type of a function that:
+
+     #1 - Takes a callback as parameter.
+
+     #2 - Wants to support arbitrary callable objects as callback type
+	  (e.g., stateful function objects, lambda closures, free
+	  functions).
+
+     #3 - Does not store the callback anywhere; instead the function
+	  just calls the callback directly or forwards it to some
+	  other function that calls it.
+
+     #4 - Can't be, or we don't want it to be, a template function
+	  with the callable type as template parameter.  For example,
+	  when the callback is a parameter of a virtual member
+	  function, or when putting the function template in a header
+	  would expose too much implementation detail.
+
+   Note that the C-style "function pointer" + "void *data" callback
+   parameter idiom fails requirement #2 above.  Please don't add new
+   uses of that idiom.  I.e., something like this wouldn't work;
+
+    typedef bool (iterate_over_foos_cb) (foo *f, void *user_data),
+    void iterate_over_foos (iterate_over_foos_cb *callback, void *user_data);
+
+    foo *find_foo_by_type (int type)
+    {
+      foo *found = nullptr;
+
+      iterate_over_foos ([&] (foo *f, void *data)
+	{
+	  if (foo->type == type)
+	    {
+	      found = foo;
+	      return true; // stop iterating
+	    }
+	  return false; // continue iterating
+	}, NULL);
+
+      return found;
+    }
+
+   The above wouldn't compile, because lambdas with captures can't be
+   implicitly converted to a function pointer (because a capture means
+   some context data must be passed to the lambda somehow).
+
+   C++11 gave us std::function as type-erased wrapper around arbitrary
+   callables, however, std::function is not an ideal fit for transient
+   callbacks such as the use case above.  For this use case, which is
+   quite pervasive, a function_view is a better choice, because while
+   function_view is light and does not require any heap allocation,
+   std::function is a heavy-weight object with value semantics that
+   generally requires a heap allocation on construction/assignment of
+   the target callable.  In addition, while it is possible to use
+   std::function in such a way that avoids most of the overhead by
+   making sure to only construct it with callables of types that fit
+   std::function's small object optimization, such as function
+   pointers and std::reference_wrapper callables, that is quite
+   inconvenient in practice, because restricting to free-function
+   callables would imply no state/capture/closure, which we need in
+   most cases, and std::reference_wrapper implies remembering to use
+   std::ref/std::cref where the callable is constructed, with the
+   added inconvenience that std::ref/std::cref have deleted rvalue-ref
+   overloads, meaning you can't use unnamed/temporary lambdas with
+   them.
+
+   Note that because function_view is a non-owning view of a callable,
+   care must be taken to ensure that the callable outlives the
+   function_view that calls it.  This is not really a problem for the
+   use case function_view is intended for, such as passing a temporary
+   function object / lambda to a function that accepts a callback,
+   because in those cases, the temporary is guaranteed to be live
+   until the called function returns.
+
+   Calling a function_view with no associated target is undefined,
+   unlike with std::function, which throws std::bad_function_call.
+   This is by design, to avoid the otherwise necessary NULL check in
+   function_view::operator().
+
+   Since function_view objects are small (a pair of pointers), they
+   should generally be passed around by value.
+
+   Usage:
+
+   Given this function that accepts a callback:
+
+    void
+    iterate_over_foos (gdb::function_view<void (foo *)> callback)
+    {
+       for (auto &foo : foos)
+	 callback (&foo);
+    }
+
+   you can call it like this, passing a lambda as callback:
+
+    iterate_over_foos ([&] (foo *f)
+      {
+	process_one_foo (f);
+      });
+
+   or like this, passing a function object as callback:
+
+    struct function_object
+    {
+      void operator() (foo *f)
+      {
+	if (s->check ())
+	  process_one_foo (f);
+      }
+
+      // some state
+      state *s;
+    };
+
+    state mystate;
+    function_object matcher {&mystate};
+    iterate_over_foos (matcher);
+
+  or like this, passing a function pointer as callback:
+
+    iterate_over_foos (process_one_foo);
+
+  You can find unit tests covering the whole API in
+  unittests/function-view-selftests.c.  */
+
+namespace gdb {
+
+namespace fv_detail {
+/* Bits shared by all function_view instantiations that do not depend
+   on the template parameters.  */
+
+/* Storage for the erased callable.  This is a union in order to be
+   able to save both a function object (data) pointer or a function
+   pointer without triggering undefined behavior.  */
+union erased_callable
+{
+  /* For function objects.  */
+  void *data;
+
+    /* For function pointers.  */
+  void (*fn) ();
+};
+
+} /* namespace fv_detail */
+
+/* Use partial specialization to get access to the callable's
+   signature. */
+template<class Signature>
+struct function_view;
+
+template<typename Res, typename... Args>
+class function_view<Res (Args...)>
+{
+  template<typename From, typename To>
+  using CompatibleReturnType
+    = Or<std::is_void<To>,
+	 std::is_same<From, To>,
+	 std::is_convertible<From, To>>;
+
+  /* True if Func can be called with Args, and either the result is
+     Res, convertible to Res or Res is void.  */
+  template<typename Callable,
+	   typename Res2 = typename std::result_of<Callable &(Args...)>::type>
+  struct IsCompatibleCallable : CompatibleReturnType<Res2, Res>
+  {};
+
+  /* True if Callable is a function_view.  Used to avoid hijacking the
+     copy ctor.  */
+  template <typename Callable>
+  struct IsFunctionView
+    : std::is_same<function_view, typename std::decay<Callable>::type>
+  {};
+
+ public:
+
+  /* NULL by default.  */
+  constexpr function_view () noexcept
+    : m_erased_callable {},
+      m_invoker {}
+  {}
+
+  /* Default copy/assignment is fine.  */
+  function_view (const function_view &) = default;
+  function_view &operator= (const function_view &) = default;
+
+  /* This is the main entry point.  Use SFINAE to avoid hijacking the
+     copy constructor and to ensure that the target type is
+     compatible.  */
+  template
+    <typename Callable,
+     typename = Requires<Not<IsFunctionView<Callable>>>,
+     typename = Requires<IsCompatibleCallable<Callable>>>
+  function_view (Callable &&callable) noexcept
+  {
+    bind (callable);
+  }
+
+  /* Construct a NULL function_view.  */
+  constexpr function_view (std::nullptr_t) noexcept
+    : m_erased_callable {},
+      m_invoker {}
+  {}
+
+  /* Clear a function_view.  */
+  function_view &operator= (std::nullptr_t) noexcept
+  {
+    m_invoker = nullptr;
+    return *this;
+  }
+
+  /* Return true if the wrapper has a target, false otherwise.  Note
+     we check M_INVOKER instead of M_ERASED_CALLABLE because we don't
+     know which member of the union is active right now.  */
+  constexpr explicit operator bool () const noexcept
+  { return m_invoker != nullptr; }
+
+  /* Call the callable.  */
+  Res operator () (Args... args) const
+  { return m_invoker (m_erased_callable, std::forward<Args> (args)...); }
+
+ private:
+
+  /* Bind this function_view to a compatible function object
+     reference.  */
+  template <typename Callable>
+  void bind (Callable &callable) noexcept
+  {
+    m_erased_callable.data = (void *) std::addressof (callable);
+    m_invoker = [] (fv_detail::erased_callable ecall, Args... args)
+      noexcept (noexcept (callable (std::forward<Args> (args)...))) -> Res
+      {
+	auto &restored_callable = *static_cast<Callable *> (ecall.data);
+	/* The explicit cast to Res avoids a compile error when Res is
+	   void and the callable returns non-void.  */
+	return (Res) restored_callable (std::forward<Args> (args)...);
+      };
+  }
+
+  /* Bind this function_view to a compatible function pointer.
+
+     Making this a separate function allows avoiding one indirection,
+     by storing the function pointer directly in the storage, instead
+     of a pointer to pointer.  erased_callable is then a union in
+     order to avoid storing a function pointer as a data pointer here,
+     which would be undefined.  */
+  template<class Res2, typename... Args2>
+  void bind (Res2 (*fn) (Args2...)) noexcept
+  {
+    m_erased_callable.fn = reinterpret_cast<void (*) ()> (fn);
+    m_invoker = [] (fv_detail::erased_callable ecall, Args... args)
+      noexcept (noexcept (fn (std::forward<Args> (args)...))) -> Res
+      {
+	auto restored_fn = reinterpret_cast<Res2 (*) (Args2...)> (ecall.fn);
+	/* The explicit cast to Res avoids a compile error when Res is
+	   void and the callable returns non-void.  */
+	return (Res) restored_fn (std::forward<Args> (args)...);
+      };
+  }
+
+  /* Storage for the erased callable.  */
+  fv_detail::erased_callable m_erased_callable;
+
+  /* The invoker.  This is set to a capture-less lambda by one of the
+     'bind' overloads.  The lambda restores the right type of the
+     callable (which is passed as first argument), and forwards the
+     args.  */
+  Res (*m_invoker) (fv_detail::erased_callable, Args...);
+};
+
+/* Allow comparison with NULL.  Defer the work to the in-class
+   operator bool implementation.  */
+
+template<typename Res, typename... Args>
+constexpr inline bool
+operator== (const function_view<Res (Args...)> &f, std::nullptr_t) noexcept
+{ return !static_cast<bool> (f); }
+
+template<typename Res, typename... Args>
+constexpr inline bool
+operator== (std::nullptr_t, const function_view<Res (Args...)> &f) noexcept
+{ return !static_cast<bool> (f); }
+
+template<typename Res, typename... Args>
+constexpr inline bool
+operator!= (const function_view<Res (Args...)> &f, std::nullptr_t) noexcept
+{ return static_cast<bool> (f); }
+
+template<typename Res, typename... Args>
+constexpr inline bool
+operator!= (std::nullptr_t, const function_view<Res (Args...)> &f) noexcept
+{ return static_cast<bool> (f); }
+
+} /* namespace gdb */
+
+#endif