target factories, target open and multiple instances of targets

Currently, to open a target, with "target TARGET_NAME", GDB finds the
target_ops instance with "TARGET_NAME" as short name, and then calls
its target_ops::open virtual method.  In reality, there's no actual
target/name lookup, a pointer to the target_ops object was associated
with the "target TARGET_NAME" command at add_target time (when GDB is
initialized), as the command's context.

This creates a chicken and egg situation.  Consider the case of
wanting to open multiple remote connections.  We want to be able to
have one remote target_ops instance per connection, but, if we're not
connected yet, so we don't yet have an instance to call target->open()
on...

This patch fixes this by separating out common info about a target_ops
to a separate structure (shortname, longname, doc), and changing the
add_target routine to take a reference to such an object instead of a
pointer to a target_ops, and a pointer to a factory function that is
responsible to open an instance of the corresponding target when the
user types "target TARGET_NAME".

 -extern void add_target (struct target_ops *);
 +extern void add_target (const target_info &info, target_open_ftype *func);

I.e. this factory function replaces the target_ops::open virtual
method.

For static/singleton targets, nothing changes, the target_open_ftype
function pushes the global target_ops instance on the target stack.
At target_close time, the connection is tor down, but the global
target_ops object remains live.

However, targets that support being open multiple times will make
their target_open_ftype routine allocate a new target_ops instance on
the heap [e.g., new remote_target()], and push that on the stack.  At
target_close time, the new object is destroyed (by the
target_ops::close virtual method).

Both the core target and the remote targets will support being open
multiple times (others could/should too, but those were my stopping
point), but not in this patch yet.  We need to get rid of more globals
first before that'd be useful.

Native targets are somewhat special, given find_default_run_target &
friends.  Those routines also expect to return a target_ops pointer,
even before we've open the target.  However, we'll never need more
than one instance of the native target, so we can assume/require that
native targets are global/simpletons, and have the backends register a
pointer to the native target_ops.  Since all native targets inherit
inf_child_target, we can centralize that registration.  See
add_inf_child_target, get_native_target/set_native_target and
find_default_run_target.

gdb/ChangeLog:
2018-05-02  Pedro Alves  <palves@redhat.com>

	* aarch64-fbsd-nat.c (_initialize_aarch64_fbsd_nat): Use
	add_inf_child_target.
	* aarch64-linux-nat.c (_initialize_aarch64_linux_nat): Use
	add_inf_child_target.
	* aix-thread.c (aix_thread_target_info): New.
	(aix_thread_target) <shortname, longname, doc>: Delete.
	<info>: New.
	* alpha-bsd-nat.c (_initialize_alphabsd_nat): Use
	add_inf_child_target.
	* alpha-linux-nat.c (_initialize_alpha_linux_nat): Use
	add_inf_child_target.
	* amd64-fbsd-nat.c (_initialize_amd64fbsd_nat): Use
	add_inf_child_target.
	* amd64-linux-nat.c (_initialize_amd64_linux_nat): Use
	add_inf_child_target.
	* amd64-nbsd-nat.c (_initialize_amd64nbsd_nat): Use
	add_inf_child_target.
	* amd64-obsd-nat.c (_initialize_amd64obsd_nat): Use
	add_inf_child_target.
	* arm-fbsd-nat.c (_initialize_arm_fbsd_nat): Use
	add_inf_child_target.
	* arm-linux-nat.c (_initialize_arm_linux_nat): Use
	add_inf_child_target.
	* arm-nbsd-nat.c (_initialize_arm_netbsd_nat): Use
	add_inf_child_target.
	* bfd-target.c (target_bfd_target_info): New.
	(target_bfd) <shortname, longname, doc>: Delete.
	<info>: New.
	* bsd-kvm.c (bsd_kvm_target_info): New.
	(bsd_kvm_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(bsd_kvm_target::open): Rename to ...
	(bsd_kvm_target_open): ... this.  Adjust.
	* bsd-uthread.c (bsd_uthread_target_info): New.
	(bsd_uthread_target) <shortname, longname, doc>: Delete.
	<info>:	New.
	* corefile.c (core_file_command): Adjust.
	* corelow.c (core_target_info): New.
	(core_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(core_target::open): Rename to ...
	(core_target_open): ... this.  Adjust.
	* ctf.c (ctf_target_info): New.
	(ctf_target) <shortname, longname, doc>: Delete.
	<info>:	New.
	(ctf_target::open): Rename to ...
	(ctf_target_open): ... this.
	(_initialize_ctf): Adjust.
	* exec.c (exec_target_info): New.
	(exec_target) <shortname, longname, doc>: Delete.
	<info>:	New.
	(exec_target::open): Rename to ...
	(exec_target_open): ... this.
	* gdbcore.h (core_target_open): Declare.
	* go32-nat.c (_initialize_go32_nat): Use add_inf_child_target.
	* hppa-linux-nat.c (_initialize_hppa_linux_nat): Use
	add_inf_child_target.
	* hppa-nbsd-nat.c (_initialize_hppanbsd_nat): Use
	add_inf_child_target.
	* hppa-obsd-nat.c (_initialize_hppaobsd_nat): Use
	add_inf_child_target.
	* i386-darwin-nat.c (_initialize_i386_darwin_nat): Use
	add_inf_child_target.
	* i386-fbsd-nat.c (_initialize_i386fbsd_nat): Use
	add_inf_child_target.
	* i386-gnu-nat.c (_initialize_i386gnu_nat): Use
	add_inf_child_target.
	* i386-linux-nat.c (_initialize_i386_linux_nat): Use
	add_inf_child_target.
	* i386-nbsd-nat.c (_initialize_i386nbsd_nat): Use
	add_inf_child_target.
	* i386-obsd-nat.c (_initialize_i386obsd_nat): Use
	add_inf_child_target.
	* ia64-linux-nat.c (_initialize_ia64_linux_nat): Use
	add_inf_child_target.
	* inf-child.c (inf_child_target_info): New.
	(inf_child_target::info): New.
	(inf_child_open_target): Remove 'target' parameter.  Use
	get_native_target instead.
	(inf_child_target::open): Delete.
	(add_inf_child_target): New.
	* inf-child.h (inf_child_target) <shortname, longname, doc, open>:
	Delete.
	<info>:	New.
	(add_inf_child_target): Declare.
	(inf_child_open_target): Declare.
	* linux-thread-db.c (thread_db_target_info): New.
	(thread_db_target) <shortname, longname, doc>: Delete.
	<info>:	New.
	* m32r-linux-nat.c (_initialize_m32r_linux_nat): Use
	add_inf_child_target.
	* m68k-bsd-nat.c (_initialize_m68kbsd_nat): Use
	add_inf_child_target.
	* m68k-linux-nat.c (_initialize_m68k_linux_nat): Use
	add_inf_child_target.
	* m88k-bsd-nat.c (_initialize_m88kbsd_nat): Use
	add_inf_child_target.
	* make-target-delegates (print_class): Adjust.
	* mips-fbsd-nat.c (_initialize_mips_fbsd_nat): Use
	add_inf_child_target.
	* mips-linux-nat.c (_initialize_mips_linux_nat): Use
	add_inf_child_target.
	* mips-nbsd-nat.c (_initialize_mipsnbsd_nat): Use
	add_inf_child_target.
	* mips64-obsd-nat.c (_initialize_mips64obsd_nat): Use
	add_inf_child_target.
	* nto-procfs.c (nto_native_target_info): New.
	(nto_procfs_target_native) <shortname, longname, doc>:
	Delete.
	<info>:	New.
	(nto_procfs_target_info): New.
	(nto_procfs_target_procfs) <shortname, longname, doc>:
	Delete.
	<info>:	New.
	(init_procfs_targets): Adjust.
	* ppc-fbsd-nat.c (_initialize_ppcfbsd_nat): Use
	add_inf_child_target.
	* ppc-linux-nat.c (_initialize_ppc_linux_nat): Use
	add_inf_child_target.
	* ppc-nbsd-nat.c (_initialize_ppcnbsd_nat): Use
	add_inf_child_target.
	* ppc-obsd-nat.c (_initialize_ppcobsd_nat): Use
	add_inf_child_target.
	* ravenscar-thread.c (ravenscar_target_info): New.
	(ravenscar_thread_target) <shortname, longname, doc>:
	Delete.
	<info>:	New.
	* record-btrace.c (record_btrace_target_info):
	(record_btrace_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(record_btrace_target::open): Rename to ...
	(record_btrace_target_open): ... this.  Adjust.
	* record-full.c (record_longname, record_doc): New.
	(record_full_base_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(record_full_target_info): New.
	(record_full_target): <shortname>: Delete.
	<info>: New.
	(record_full_core_open_1, record_full_open_1): Update comments.
	(record_full_base_target::open): Rename to ...
	(record_full_open): ... this.
	(cmd_record_full_restore): Update.
	(_initialize_record_full): Update.
	* remote-sim.c (remote_sim_target_info): New.
	(gdbsim_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(gdbsim_target::open): Rename to ...
	(gdbsim_target_open): ... this.
	(_initialize_remote_sim): Adjust.
	* remote.c (remote_doc): New.
	(remote_target_info): New.
	(remote_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(extended_remote_target_info): New.
	(extended_remote_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(remote_target::open_1): Make static.  Adjust.
	* rs6000-nat.c (_initialize_rs6000_nat): Use add_inf_child_target.
	* s390-linux-nat.c (_initialize_s390_nat): Use
	add_inf_child_target.
	* sh-nbsd-nat.c (_initialize_shnbsd_nat): Use
	add_inf_child_target.
	* sol-thread.c (thread_db_target_info): New.
	(sol_thread_target) <shortname, longname, doc>: Delete.
	<info>: New.
	* sparc-linux-nat.c (_initialize_sparc_linux_nat): Use
	add_inf_child_target.
	* sparc-nbsd-nat.c (_initialize_sparcnbsd_nat): Use
	add_inf_child_target.
	* sparc64-fbsd-nat.c (_initialize_sparc64fbsd_nat): Use
	add_inf_child_target.
	* sparc64-linux-nat.c (_initialize_sparc64_linux_nat): Use
	add_inf_child_target.
	* sparc64-nbsd-nat.c (_initialize_sparc64nbsd_nat): Use
	add_inf_child_target.
	* sparc64-obsd-nat.c (_initialize_sparc64obsd_nat): Use
	add_inf_child_target.
	* spu-linux-nat.c (_initialize_spu_nat): Use
	add_inf_child_target.
	* spu-multiarch.c (spu_multiarch_target_info): New.
	(spu_multiarch_target) <shortname, longname, doc>: Delete.
	<info>: New.
	* target-delegates.c: Regenerate.
	* target.c: Include <unordered_map>.
	(target_ops_p): Delete.
	(DEF_VEC_P(target_ops_p)): Delete.
	(target_factories): New.
	(test_target_info): New.
	(test_target_ops::info): New.
	(open_target): Adjust to use target_factories.
	(add_target_with_completer): Rename to ...
	(add_target): ... this.  Change prototype.  Register target_info
	and open callback in target_factories.  Register target_info in
	command context instead of target_ops.
	(add_target): Delete old implementation.
	(add_deprecated_target_alias): Change prototype.  Adjust.
	(the_native_target): New.
	(set_native_target, get_native_target): New.
	(find_default_run_target): Use the_native_target.
	(find_attach_target, find_run_target): Simplify.
	(target_ops::open): Delete.
	(dummy_target_info): New.
	(dummy_target::shortname, dummy_target::longname)
	(dummy_target::doc): Delete.
	(dummy_target::info): New.
	(debug_target::shortname, debug_target::longname)
	(debug_target::doc): Delete.
	(debug_target::info): New.
	* target.h (struct target_info): New.
	(target_ops::~target_ops): Add comment.
	(target_ops::info): New.
	(target_ops::shortname, target_ops::longname, target_ops::doc): No
	longer virtual.  Implement in terms of target_info.
	(set_native_target, get_native_target): Declare.
	(target_open_ftype): New.
	(add_target, add_target_with_completer)
	(add_deprecated_target_alias): Change prototype.
	(test_target) <shortname, longname, doc>: Delete.
	<info>: New.
	* tilegx-linux-nat.c (_initialize_tile_linux_nat): Use
	add_inf_child_target.
	* tracefile-tfile.c (tfile_target_info): New.
	(tfile_target) <shortname, longname, doc>: Delete.
	<info>: New.
	(tfile_target::open): Rename to ...
	(tfile_target_open): ... this.
	(_initialize_tracefile_tfile): Adjust.
	* vax-bsd-nat.c (_initialize_vaxbsd_nat): Use
	add_inf_child_target.
	* windows-nat.c (_initialize_windows_nat): Use
	add_inf_child_target.
	* xtensa-linux-nat.c (_initialize_xtensa_linux_nat): Use
	add_inf_child_target.

1 files changed, 56 insertions, 33 deletions

diff --git a/gdb/target.h b/gdb/target.h
index cd49fce..b37702b 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -404,27 +404,44 @@ typedef void async_callback_ftype (enum inferior_event_type event_type,
 #define TARGET_DEFAULT_RETURN(ARG)
 #define TARGET_DEFAULT_FUNC(ARG)
 
+/* Each target that can be activated with "target TARGET_NAME" passes
+   the address of one of these objects to add_target, which uses the
+   object's address as unique identifier, and registers the "target
+   TARGET_NAME" command using SHORTNAME as target name.  */
+
+struct target_info
+{
+  /* Name of this target.  */
+  const char *shortname;
+
+  /* Name for printing.  */
+  const char *longname;
+
+  /* Documentation.  Does not include trailing newline, and starts
+     with a one-line description (probably similar to longname).  */
+  const char *doc;
+};
+
 struct target_ops
   {
     struct target_ops *beneath;	/* To the target under this one.  */
 
+    /* Free resources associated with the target.  Note that singleton
+       targets, like e.g., native targets, are global objects, not
+       heap allocated, and are thus only deleted on GDB exit.  The
+       main teardown entry point is the "close" method, below.  */
     virtual ~target_ops () {}
 
-    /* Name this target type.  */
-    virtual const char *shortname () = 0;
-
-    /* Name for printing.  */
-    virtual const char *longname () = 0;
+    /* Return a reference to this target's unique target_info
+       object.  */
+    virtual const target_info &info () const = 0;
 
-    /* Documentation.  Does not include trailing newline, and starts
-       ith a one-line description (probably similar to longname).  */
-    virtual const char *doc () = 0;
+    /* Name this target type.  */
+    const char *shortname ()
+    { return info ().shortname; }
 
-    /* The open routine takes the rest of the parameters from the
-       command, and (if successful) pushes a new target onto the
-       stack.  Targets should supply this routine, if only to provide
-       an error message.  */
-    virtual void open (const char *, int);
+    const char *longname ()
+    { return info ().longname; }
 
     /* Close the target.  This is where the target can handle
        teardown.  Heap-allocated targets should delete themselves
@@ -1226,6 +1243,15 @@ struct target_ops
       TARGET_DEFAULT_IGNORE ();
   };
 
+/* Native target backends call this once at initialization time to
+   inform the core about which is the target that can respond to "run"
+   or "attach".  Note: native targets are always singletons.  */
+extern void set_native_target (target_ops *target);
+
+/* Get the registered native target, if there's one.  Otherwise return
+   NULL.  */
+extern target_ops *get_native_target ();
+
 /* The ops structure for our "current" target process.  This should
    never be NULL.  If there is no target, it points to the dummy_target.  */
 
@@ -2207,15 +2233,25 @@ int target_verify_memory (const gdb_byte *data,
    no matter where it is on the list.  Returns 0 if no
    change, 1 if removed from stack.  */
 
-extern void add_target (struct target_ops *);
+/* Type of callback called when the user activates a target with
+   "target TARGET_NAME".  The callback routine takes the rest of the
+   parameters from the command, and (if successful) pushes a new
+   target onto the stack.  */
+typedef void target_open_ftype (const char *args, int from_tty);
+
+/* Add the target described by INFO to the list of possible targets
+   and add a new command 'target $(INFO->shortname)'.  Set COMPLETER
+   as the command's completer if not NULL.  */
 
-extern void add_target_with_completer (struct target_ops *t,
-				       completer_ftype *completer);
+extern void add_target (const target_info &info,
+			target_open_ftype *func,
+			completer_ftype *completer = NULL);
 
-/* Adds a command ALIAS for target T and marks it deprecated.  This is useful
-   for maintaining backwards compatibility when renaming targets.  */
+/* Adds a command ALIAS for the target described by INFO and marks it
+   deprecated.  This is useful for maintaining backwards compatibility
+   when renaming targets.  */
 
-extern void add_deprecated_target_alias (struct target_ops *t,
+extern void add_deprecated_target_alias (const target_info &info,
 					 const char *alias);
 
 extern void push_target (struct target_ops *);
@@ -2466,20 +2502,7 @@ public:
     to_stratum = process_stratum;
   }
 
-  const char *shortname () override
-  {
-    return NULL;
-  }
-
-  const char *longname () override
-  {
-    return NULL;
-  }
-
-  const char *doc () override
-  {
-    return NULL;
-  }
+  const target_info &info () const override;
 
   bool has_registers () override
   {