[PATCH 3/4] gdb: use python to colorize disassembler output

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

This commit adds styling support to the disassembler output, as such
two new commands are added to GDB:

  set style disassembler on|off
  show style disassembler

In this commit I make use of the Python Pygments package to provide
the styling.  I did investigate making use of libsource-highlight,
however, I found the highlighting results to be inferior to those of
Pygments; only some mnemonics were highlighted, and highlighting of
register names such as r9d and r8d (on x86-64) was incorrect.

To enable disassembler highlighting via Pygments, I've added a new
extension language hook, which is then implemented for Python.  This
hook is very similar to the existing hook for source code
colorization.

One possibly odd choice I made with the new hook is to pass a
gdb.Architecture through, even though this is currently unused.  The
reason this argument is not used is that, currently, styling is
performed identically for all architectures.

However, even though the Python function used to perform styling of
disassembly output is not part of any undocumented API, I don't want
to close the door on a user overriding this function to provide
architecture specific styling.  To do this, the user would inevitably
require access to the gdb.Architecture, and so I decided to add this
field now.

The styling is applied within gdb_disassembler::print_insn, to achieve
this, gdb_disassembler now writes its output into a temporary buffer,
styling is then applied to the contents of this buffer.  Finally the
gdb_disassembler buffer is copied out to its final destination stream.

There's a new test to check that the disassembler output includes some
escape sequences, though I don't check for specific colours; the
precise colors will depend on which instructions are in the
disassembler output.

The only negative change with this commit relates to how addresses are
printed, in the case when the Python Pygments package is not
available.  Addresses are printed via calls to GDB's print_address
function.  Traditionally, this would provide styling for the address
and symbol name if the output ui_file* supported styling.  Now that we
want to apply styling after the disassembler has finished, all
disassembler output is written into a temporary string_file, which is
configured not to support styling.  As a result, the print_address
call no longer performs styling.

If Pygments is available, this isn't a huge problem, the output will
be fully styled one the disassembler has finished.  However, if
Pygments is not available, or fails for some reason, then, it is now
too late to go back and have print_address apply styling.  We have
lost all print_address styling in this case.

I don't know how much of a problem this is, for me, having the
disassembler fully styled is a big enough win.  But, if people see
this as a huge problem we can investigate mechanisms to restore the
print_address styling (for the case where Pygments is not available).
---
 gdb/NEWS                         |  6 +++
 gdb/cli/cli-style.c              | 26 +++++++++++
 gdb/cli/cli-style.h              |  3 ++
 gdb/disasm.c                     | 23 +++++++++-
 gdb/disasm.h                     |  6 +++
 gdb/doc/gdb.texinfo              | 15 +++++++
 gdb/extension-priv.h             |  6 +++
 gdb/extension.c                  | 20 +++++++++
 gdb/extension.h                  |  8 ++++
 gdb/python/lib/gdb/__init__.py   | 11 +++++
 gdb/python/python.c              | 74 ++++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/style.exp | 46 +++++++++++++++++---
 12 files changed, 236 insertions(+), 8 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index d001a03145d..37c58c527a9 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -32,6 +32,12 @@ maint show internal-warning backtrace
   internal-error, or an internal-warning.  This is on by default for
   internal-error and off by default for internal-warning.
 
+set style disassembly on|off
+show style disassembly
+  If GDB is compiled with Python support, and the Python Pygments
+  package is available, then, when this setting is on, disassembler
+  output will have styling applied.
+
 * Python API
 
   ** New function gdb.add_history(), which takes a gdb.Value object
diff --git a/gdb/cli/cli-style.c b/gdb/cli/cli-style.c
index 228fa698c13..d4e49e3df5b 100644
--- a/gdb/cli/cli-style.c
+++ b/gdb/cli/cli-style.c
@@ -38,6 +38,11 @@ bool cli_styling = true;
 
 bool source_styling = true;
 
+/* True if disassembler styling is enabled.  Note that this is only
+   consulted when cli_styling is true.  */
+
+bool disassembler_styling = true;
+
 /* Name of colors; must correspond to ui_file_style::basic_color.  */
 static const char * const cli_colors[] = {
   "none",
@@ -302,6 +307,18 @@ show_style_sources (struct ui_file *file, int from_tty,
     fprintf_filtered (file, _("Source code styling is disabled.\n"));
 }
 
+/* Implement 'show style disassembler'.  */
+
+static void
+show_style_disassembler (struct ui_file *file, int from_tty,
+			 struct cmd_list_element *c, const char *value)
+{
+  if (disassembler_styling)
+    fprintf_filtered (file, _("Disassembler output styling is enabled.\n"));
+  else
+    fprintf_filtered (file, _("Disassembler output styling is disabled.\n"));
+}
+
 void _initialize_cli_style ();
 void
 _initialize_cli_style ()
@@ -337,6 +354,15 @@ available if the appropriate extension is available at runtime."
 			   ), set_style_enabled, show_style_sources,
 			   &style_set_list, &style_show_list);
 
+  add_setshow_boolean_cmd ("disassembler", no_class, &disassembler_styling, _("\
+Set whether disassembler output styling is enabled."), _("\
+Show whether disassembler output styling is enabled."), _("\
+If enabled, disassembler output is styled.  Disassembler highlighting\n\
+requires the Python Pygments library, if this library is not available\n\
+then disassembler highlighting will not be possible."
+			   ), set_style_enabled, show_style_disassembler,
+			   &style_set_list, &style_show_list);
+
   file_name_style.add_setshow_commands (no_class, _("\
 Filename display styling.\n\
 Configure filename colors and display intensity."),
diff --git a/gdb/cli/cli-style.h b/gdb/cli/cli-style.h
index 78bc2cd6f1e..5361a644a95 100644
--- a/gdb/cli/cli-style.h
+++ b/gdb/cli/cli-style.h
@@ -128,6 +128,9 @@ extern cli_style_option version_style;
 /* True if source styling is enabled.  */
 extern bool source_styling;
 
+/* True if disassembler styling is enabled.  */
+extern bool disassembler_styling;
+
 /* True if styling is enabled.  */
 extern bool cli_styling;
 
diff --git a/gdb/disasm.c b/gdb/disasm.c
index c045dfc94a6..29755c9aa23 100644
--- a/gdb/disasm.c
+++ b/gdb/disasm.c
@@ -753,9 +753,10 @@ get_all_disassembler_options (struct gdbarch *gdbarch)
 gdb_disassembler::gdb_disassembler (struct gdbarch *gdbarch,
 				    struct ui_file *file,
 				    di_read_memory_ftype read_memory_func)
-  : m_gdbarch (gdbarch)
+  : m_gdbarch (gdbarch),
+    m_dest (file)
 {
-  init_disassemble_info (&m_di, file, dis_asm_fprintf);
+  init_disassemble_info (&m_di, &m_buffer, dis_asm_fprintf);
   m_di.flavour = bfd_target_unknown_flavour;
   m_di.memory_error_func = dis_asm_memory_error;
   m_di.print_address_func = dis_asm_print_address;
@@ -789,9 +790,27 @@ gdb_disassembler::print_insn (CORE_ADDR memaddr,
 			      int *branch_delay_insns)
 {
   m_err_memaddr.reset ();
+  m_buffer.clear ();
 
   int length = gdbarch_print_insn (arch (), memaddr, &m_di);
 
+  /* If we have successfully disassembled an instruction, and styling is
+     on, and possible, then style the disassembler output.  */
+  if (length > 0 && disassembler_styling
+      && m_dest->can_emit_style_escape ())
+    {
+      gdb::optional<std::string> ext_contents;
+      ext_contents = ext_lang_colorize_disasm (m_buffer.string (), arch ());
+      if (ext_contents.has_value ())
+	m_buffer.string () = std::move (*ext_contents);
+    }
+
+  /* Push any disassemble output to the real destination stream.  We do
+     this even if the disassembler reported failure (-1) as the
+     disassembler may have printed something to its output stream.  */
+  m_di.fprintf_func (m_dest, "%s", m_buffer.c_str ());
+
+  /* If the disassembler failed then report an appropriate error.  */
   if (length < 0)
     {
       if (m_err_memaddr.has_value ())
diff --git a/gdb/disasm.h b/gdb/disasm.h
index f6de33e3db8..0e768f767c1 100644
--- a/gdb/disasm.h
+++ b/gdb/disasm.h
@@ -82,6 +82,12 @@ class gdb_disassembler
      non-memory error.  */
   gdb::optional<CORE_ADDR> m_err_memaddr;
 
+  /* Disassembler output is built up into this buffer.  */
+  string_file m_buffer;
+
+  /* The stream to which disassembler output will be written.  */
+  ui_file *m_dest;
+
   static int dis_asm_fprintf (void *stream, const char *format, ...)
     ATTRIBUTE_PRINTF(2,3);
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 631a7c03b31..6644bd517ff 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -26071,6 +26071,21 @@
 
 @item show style sources
 Show the current state of source code styling.
+
+@item set style disassembly @samp{on|off}
+Enable or disable disassembly styling.  This affects whether
+disassembly output, such as the output of the @code{disassemble}
+command, is styled.  Disassembly styling only works if styling in
+general is enabled (with @code{set style enabled on}), and if a source
+highlighting library is available to @value{GDBN}.
+
+To highlight disassembler output, @value{GDBN} must be compiled with
+Python support, and the Python Pygments package must be available.  If
+these requirements are not met then @value{GDBN} will not highlight
+disassembler output, even when this option is @samp{on}.
+
+@item show style disassembly
+Show the current state of disassembly styling.
 @end table
 
 Subcommands of @code{set style} control specific forms of styling.
diff --git a/gdb/extension-priv.h b/gdb/extension-priv.h
index 77f23e0f911..b2150624dde 100644
--- a/gdb/extension-priv.h
+++ b/gdb/extension-priv.h
@@ -257,6 +257,12 @@ struct extension_language_ops
      or an empty option.  */
   gdb::optional<std::string> (*colorize) (const std::string &name,
 					  const std::string &contents);
+
+  /* Colorize a single line of disassembler output, CONTENT.  This should
+     either return colorized (using ANSI terminal escapes) version of the
+     contents, or an empty optional.  */
+  gdb::optional<std::string> (*colorize_disasm) (const std::string &content,
+						 gdbarch *gdbarch);
 };
 
 /* State necessary to restore a signal handler to its previous value.  */
diff --git a/gdb/extension.c b/gdb/extension.c
index 89ab29f3d1c..6862147ac2f 100644
--- a/gdb/extension.c
+++ b/gdb/extension.c
@@ -904,6 +904,26 @@ ext_lang_colorize (const std::string &filename, const std::string &contents)
   return result;
 }
 
+/* See extension.h.  */
+
+gdb::optional<std::string>
+ext_lang_colorize_disasm (const std::string &content, gdbarch *gdbarch)
+{
+  gdb::optional<std::string> result;
+
+  for (const struct extension_language_defn *extlang : extension_languages)
+    {
+      if (extlang->ops == nullptr
+	  || extlang->ops->colorize_disasm == nullptr)
+	continue;
+      result = extlang->ops->colorize_disasm (content, gdbarch);
+      if (result.has_value ())
+	return result;
+    }
+
+  return result;
+}
+
 /* Called via an observer before gdb prints its prompt.
    Iterate over the extension languages giving them a chance to
    change the prompt.  The first one to change the prompt wins,
diff --git a/gdb/extension.h b/gdb/extension.h
index 2f2ca3e7743..e8d2fbc7fc3 100644
--- a/gdb/extension.h
+++ b/gdb/extension.h
@@ -319,6 +319,14 @@ extern void get_matching_xmethod_workers
 extern gdb::optional<std::string> ext_lang_colorize
   (const std::string &filename, const std::string &contents);
 
+/* Try to colorize a single line of disassembler output, CONTENT for
+   GDBARCH.  This will return either a colorized (using ANSI terminal
+   escapes) version of CONTENT, or an empty value if colorizing could not
+   be done.  */
+
+extern gdb::optional<std::string> ext_lang_colorize_disasm
+  (const std::string &content, gdbarch *gdbarch);
+
 #if GDB_SELF_TEST
 namespace selftests {
 extern void (*hook_set_active_ext_lang) ();
diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index 7b6d8701548..6ab797c8c5e 100644
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -243,8 +243,19 @@ try:
         except:
             return None
 
+    def colorize_disasm(content, gdbarch):
+        # Don't want any errors.
+        try:
+            lexer = lexers.get_lexer_by_name("asm")
+            formatter = formatters.TerminalFormatter()
+            return highlight(content, lexer, formatter).rstrip()
+        except:
+            return None
 
 except:
 
     def colorize(filename, contents):
         return None
+
+    def colorize_disasm(content, gdbarch):
+        return None
diff --git a/gdb/python/python.c b/gdb/python/python.c
index c7b5e7faa8e..1bf32c36329 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -121,6 +121,8 @@ static enum ext_lang_rc gdbpy_before_prompt_hook
   (const struct extension_language_defn *, const char *current_gdb_prompt);
 static gdb::optional<std::string> gdbpy_colorize
   (const std::string &filename, const std::string &contents);
+static gdb::optional<std::string> gdbpy_colorize_disasm
+  (const std::string &content, gdbarch *gdbarch);
 
 /* The interface between gdb proper and loading of python scripts.  */
 
@@ -162,6 +164,8 @@ static const struct extension_language_ops python_extension_ops =
   gdbpy_get_matching_xmethod_workers,
 
   gdbpy_colorize,
+
+  gdbpy_colorize_disasm,
 };
 
 /* The main struct describing GDB's interface to the Python
@@ -1181,6 +1185,76 @@ gdbpy_colorize (const std::string &filename, const std::string &contents)
   return std::string (PyBytes_AsString (host_str.get ()));
 }
 
+/* This is the extension_language_ops.colorize_disasm "method".  */
+
+static gdb::optional<std::string>
+gdbpy_colorize_disasm (const std::string &content, gdbarch *gdbarch)
+{
+  if (!gdb_python_initialized)
+    return {};
+
+  gdbpy_enter enter_py (get_current_arch (), current_language);
+
+  if (gdb_python_module == nullptr
+      || !PyObject_HasAttrString (gdb_python_module, "colorize_disasm"))
+    return {};
+
+  gdbpy_ref<> hook (PyObject_GetAttrString (gdb_python_module,
+					    "colorize_disasm"));
+  if (hook == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  if (!PyCallable_Check (hook.get ()))
+    return {};
+
+  gdbpy_ref<> content_arg (PyString_FromString (content.c_str ()));
+  if (content_arg == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  gdbpy_ref<> gdbarch_arg (gdbarch_to_arch_object (gdbarch));
+  if (gdbarch_arg == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  gdbpy_ref<> result (PyObject_CallFunctionObjArgs (hook.get (),
+						    content_arg.get (),
+						    gdbarch_arg.get (),
+						    nullptr));
+  if (result == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  if (!gdbpy_is_string (result.get ()))
+    return {};
+
+  gdbpy_ref<> unic = python_string_to_unicode (result.get ());
+  if (unic == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+  gdbpy_ref<> host_str (PyUnicode_AsEncodedString (unic.get (),
+						   host_charset (),
+						   nullptr));
+  if (host_str == nullptr)
+    {
+      gdbpy_print_stack ();
+      return {};
+    }
+
+  return std::string (PyBytes_AsString (host_str.get ()));
+}
+
 \f
 
 /* Printing.  */
diff --git a/gdb/testsuite/gdb.base/style.exp b/gdb/testsuite/gdb.base/style.exp
index 91d3059612d..d1fa30fb5f0 100644
--- a/gdb/testsuite/gdb.base/style.exp
+++ b/gdb/testsuite/gdb.base/style.exp
@@ -182,12 +182,25 @@ proc run_style_tests { } {
 
 	gdb_test_no_output "set width 0"
 
-	set main [limited_style main function]
-	set func [limited_style some_called_function function]
-	# Somewhere should see the call to the function.
-	gdb_test "disassemble main" \
-	    [concat "Dump of assembler code for function $main:.*" \
-		 "[limited_style $hex address].*$func.*"]
+	# Disassembly highlighting is done by Python, so, if the
+	# required modules are not available we'll not get the full
+	# highlighting.
+	if { $::python_disassembly_highlighting } {
+	    # Check that the header line of the disassembly output is
+	    # styled correctly, the address at the start of the first
+	    # disassembly line is styled correctly, and that there is at
+	    # least one escape sequence in the disassembly output.
+	    set main [limited_style main function]
+	    gdb_test "disassemble main" \
+		[concat "Dump of assembler code for function $main:\\r\\n" \
+		     "\\s+[limited_style $hex address]\\s+<\\+$decimal>:\[^\\r\\n\]+\033\\\[${decimal}\[^\\r\\n\]+.*" ""]
+	} else {
+	    set main [limited_style main function]
+	    # Somewhere should see the call to the function.
+	    gdb_test "disassemble main" \
+		[concat "Dump of assembler code for function $main:.*" \
+		     "[limited_style $hex address].*<some_called_function>.*"]
+	}
 
 	set ifield [limited_style int_field variable]
 	set sfield [limited_style string_field variable]
@@ -312,6 +325,27 @@ proc test_startup_version_string { } {
     gdb_test "" "${vers}.*" "version is styled at startup"
 }
 
+# Check to see if the Python highlighting of disassembler output is
+# expected or not, this highlighting requires Python support in GDB,
+# and the Python pygments module to be available.
+clean_restart ${binfile}
+if {![skip_python_tests]} {
+    gdb_test_multiple "python import pygments" "" {
+	-re "ModuleNotFoundError: No module named 'pygments'.*$gdb_prompt $" {
+	    set python_disassembly_highlighting false
+	}
+	-re "ImportError: No module named pygments.*$gdb_prompt $" {
+	    set python_disassembly_highlighting false
+	}
+	-re "^python import pygments\r\n$gdb_prompt $" {
+	    set python_disassembly_highlighting true
+	}
+    }
+} else {
+    set python_disassembly_highlighting false
+}
+
+verbose -log "APB: run python tests? ${python_disassembly_highlighting}"
 
 # Run tests with all styles in their default state.
 with_test_prefix "all styles enabled" {
-- 
2.25.4