Re: [PATCH 1/2] gdb: Allow target description to be dumped even when it is remote

[Andrew Burgess <andrew.burgess@embecosm.com>]

* Pedro Alves <palves@redhat.com> [2020-06-11 12:33:08 +0100]:

> On 6/11/20 11:41 AM, Andrew Burgess wrote:
> > The maintenance command 'maintenance print c-tdesc' can only print the
> > target description if it was loaded from a local file, or if the local
> > filename is passed to the maintenance command as an argument.
> > 
> > Sometimes it would be nice to know what target description GDB was
> > given by the remote, however, if I connect to a remote target and try
> > this command I see this:
> > 
> >   (gdb) maintenance print c-tdesc
> >   The current target description did not come from an XML file.
> >   (gdb)
> > 
> > Which is not very helpful.
> > 
> > This commit changes things so that if the description came from the
> > remote end then GDB will use the fake filename 'target.xml' as the
> > filename for the description, GDB will then create the C description
> > of the target as if it was in a file 'target.xml'.
> > 
> > I originally added this functionality so I could inspect the
> > description passed to GDB by the remote target.  After using this for
> > a while I realised that actually having GDB recreate the XML would be
> > even better, so a later commit will add that functionality too.
> > 
> > Still, given how small this patch is I thought it might be nice to
> > include this in GDB anyway.
> > 
> > While I was working on this anyway I've added filename command
> > completion to this command.
> > 
> > gdb/ChangeLog:
> > 
> > 	* target-descriptions.c (maint_print_c_tdesc_cmd): Use fake
> > 	filename for target descriptions that came from the target.
> > 	(_initialize_target_descriptions): Add filename command completion
> > 	for 'maint print c-tdesc'.
> > ---
> >  gdb/ChangeLog             |  7 +++++++
> >  gdb/target-descriptions.c | 14 ++++++++++----
> >  2 files changed, 17 insertions(+), 4 deletions(-)
> > 
> > diff --git a/gdb/target-descriptions.c b/gdb/target-descriptions.c
> > index 20a3a640f4f..55ea416d69a 100644
> > --- a/gdb/target-descriptions.c
> > +++ b/gdb/target-descriptions.c
> > @@ -1680,7 +1680,12 @@ maint_print_c_tdesc_cmd (const char *args, int from_tty)
> >      error (_("There is no target description to print."));
> >  
> >    if (filename == NULL)
> > -    error (_("The current target description did not come from an XML file."));
> > +    {
> > +      printf_unfiltered (_("The current target description was fetched "
> > +			   "from the target, using\n'target.xml' as a fake "
> > +			   "filename.\n\n"));
> 
> That "," makes it read a little bit ambiguously.  Try reading the sentence
> without the "," to see what I mean:
> 
>   The current target description was fetched from the target using
>  'target.xml' as a fake filename.
> 
> This can be read as GDB having read the remote fake 'target.xml' filename,
> like:
>   fetch_available_features_from_target ("target.xml", ops);
> which is what it always does anyway...
> 
> I'd suggest a hard period (and line break after the period) instead:
> 
>   The current target description was fetched from the target.
>   Using 'target.xml' as a fake filename.
> 
> But, why do we need to provide a fake name at all?  Isn't the only use of
> that filename to print it in the comment, here:
> 
>  /* THIS FILE IS GENERATED.  -*- buffer-read-only: t -*- vi:set ro:
>    Original: target.xml */
> 
> How about just doing this:

No, the filename is used in a couple of other places too, object names
are created based on the filename as well.  Still I took your idea and
went with it.

The patch below uses 'fetched from target' as the fake filename
instead.  I needed one small extra change so that 'fetched from
target' could become 'fetched_from_target' when creating C++ variable
names, but otherwise this seem fine to me.

How's this?

Thanks,
Andrew

---

commit 7426b6d447cc764cfe5a23486ad8af95ec46d2fc
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Tue Jun 9 19:00:55 2020 +0100

    gdb: Allow target description to be dumped even when it is remote
    
    The maintenance command 'maintenance print c-tdesc' can only print the
    target description if it was loaded from a local file, or if the local
    filename is passed to the maintenance command as an argument.
    
    Sometimes it would be nice to know what target description GDB was
    given by the remote, however, if I connect to a remote target and try
    this command I see this:
    
      (gdb) maintenance print c-tdesc
      The current target description did not come from an XML file.
      (gdb)
    
    Which is not very helpful.
    
    This commit changes things so that if the description came from the
    remote end then GDB will use a fake filename 'fetched from target' as
    the filename for the description, GDB will then create the C
    description of the target as though it came from this file.  Example
    output would look like this (I snipped the feature creation from the
    middle as that hasn't changed):
    
      (gdb) maintenance print c-tdesc
      /* THIS FILE IS GENERATED.  -*- buffer-read-only: t -*- vi:set ro:
        Original: fetched from target */
    
      #include "defs.h"
      #include "osabi.h"
      #include "target-descriptions.h"
    
      struct target_desc *tdesc_fetched_from_target;
      static void
      initialize_tdesc_fetched_from_target (void)
      {
        struct target_desc *result = allocate_target_description ();
        struct tdesc_feature *feature;
    
        /* ... features created here ... */
    
        tdesc_fetched_from_target = result;
      }
      (gdb)
    
    I originally added this functionality so I could inspect the
    description passed to GDB by the remote target.  After using this for
    a while I realised that actually having GDB recreate the XML would be
    even better, so a later commit will add that functionality too.
    
    Still, given how small this patch is I thought it might be nice to
    include this in GDB anyway.
    
    While I was working on this anyway I've added filename command
    completion to this command.
    
    gdb/ChangeLog:
    
            * target-descriptions.c (print_c_tdesc::print_c_tdesc): Change
            whitespace to underscore.
            (maint_print_c_tdesc_cmd): Use fake filename for target
            descriptions that came from the target.
            (_initialize_target_descriptions): Add filename command completion
            for 'maint print c-tdesc'.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 26310c429b3..d358ff4ace0 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2020-06-10  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* target-descriptions.c (print_c_tdesc::print_c_tdesc): Change
+	whitespace to underscore.
+	(maint_print_c_tdesc_cmd): Use fake filename for target
+	descriptions that came from the target.
+	(_initialize_target_descriptions): Add filename command completion
+	for 'maint print c-tdesc'.
+
 2020-06-08  Simon Marchi  <simon.marchi@efficios.com>
 
 	* gdbtypes.h (TYPE_FIELD_TYPE): Remove.  Change all call sites
diff --git a/gdb/target-descriptions.c b/gdb/target-descriptions.c
index 20a3a640f4f..da6cb76404c 100644
--- a/gdb/target-descriptions.c
+++ b/gdb/target-descriptions.c
@@ -1270,6 +1270,8 @@ class print_c_tdesc : public tdesc_element_visitor
 	break;
       else if (*inp == '-')
 	*outp++ = '_';
+      else if (*inp == ' ')
+	*outp++ = '_';
       else
 	*outp++ = *inp;
     *outp = '\0';
@@ -1680,7 +1682,7 @@ maint_print_c_tdesc_cmd (const char *args, int from_tty)
     error (_("There is no target description to print."));
 
   if (filename == NULL)
-    error (_("The current target description did not come from an XML file."));
+    filename = "fetched from target";
 
   std::string filename_after_features (filename);
   auto loc = filename_after_features.rfind ("/features/");
@@ -1811,6 +1813,8 @@ void _initialize_target_descriptions ();
 void
 _initialize_target_descriptions ()
 {
+  cmd_list_element *cmd;
+
   tdesc_data = gdbarch_data_register_pre_init (tdesc_data_init);
 
   add_basic_prefix_cmd ("tdesc", class_maintenance, _("\
@@ -1842,11 +1846,10 @@ Unset the file to read for an XML target description.\n\
 When unset, GDB will read the description from the target."),
 	   &tdesc_unset_cmdlist);
 
-  add_cmd ("c-tdesc", class_maintenance, maint_print_c_tdesc_cmd, _("\
+  cmd = add_cmd ("c-tdesc", class_maintenance, maint_print_c_tdesc_cmd, _("\
 Print the current target description as a C source file."),
 	   &maintenanceprintlist);
-
-  cmd_list_element *cmd;
+  set_cmd_completer (cmd, filename_completer);
 
   cmd = add_cmd ("xml-descriptions", class_maintenance,
 		 maintenance_check_xml_descriptions, _("\