diff mbox

[v7,2/2] Implement pahole-like 'ptype /o' option

Message ID 20171215011247.7396-3-sergiodj@redhat.com
State New
Headers show

Commit Message

Sergio Durigan Junior Dec. 15, 2017, 1:12 a.m. UTC
This commit implements the pahole-like '/o' option for 'ptype', which
prints the offsets and sizes of struct fields, reporting whenever
there is a hole found.

The output is heavily based on pahole(1), with a few modifications
here and there to adjust it to our reality.  Here's an example:

  /* offset    |  size */  type = struct wer : public tuv {
			   public:
  /*   32      |    24 */    struct tyu {
  /*   32:31   |     4 */        int a1 : 1;
  /*   32:28   |     4 */        int a2 : 3;
  /*   32: 5   |     4 */        int a3 : 23;
  /*   35: 3   |     1 */        char a4 : 2;
  /* XXX  3-bit hole   */
  /* XXX  4-byte hole  */
  /*   40      |     8 */        int64_t a5;
  /*   48:27   |     4 */        int a6 : 5;
  /*   48:56   |     8 */        int64_t a7 : 3;

				 /* total size (bytes):   24 */
			     } a1;

			     /* total size (bytes):   56 */
			   }

A big part of this patch handles the formatting logic of 'ptype',
which is a bit messy.  The code to handle bitfield offsets, however,
took some time to craft.  My thanks to Pedro Alves for figuring things
out and pointing me to the right direction, as well as coming up with
a way to inspect the layout of structs with bitfields (see testcase
for comments).

After many discussions both on IRC and at the mailing list, I tried to
implement printing vtables and inherited classes.  Unfortunately the
code grew too complex and there were still a few corner cases failing
so I had to drop the attempt.  This should be implemented in a future
patch.

This patch is the start of a long-term work I'll do to flush the local
patches we carry for Fedora GDB.  In this specific case, I'm aiming at
upstreaming the feature implemented by the 'pahole.py' script that is
shipped with Fedora GDB:

  <https://src.fedoraproject.org/rpms/gdb/blob/master/f/gdb-archer.patch#_311>

This has been regression-tested on the BuildBot.  There's a new
testcase for it, along with an update to the documentation.  I also
thought it was worth mentioning this feature in the NEWS file.

gdb/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	PR cli/16224
	* NEWS (Changes since GDB 8.0): Mention new '/o' flag.
	* c-typeprint.c (OFFSET_SPC_LEN): New define.
	(c_type_print_varspec_prefix): New argument 'struct
	print_offset_data *'.
	(c_type_print_base_1): New function and prototype.
	(c_print_type_1): New function, with code from 'c_print_type'.
	(c_print_type): Use 'c_print_type_1'.
	(c_type_print_varspec_prefix): New argument 'struct
	print_offset_data *'.  Use it.  Call 'c_type_print_base_1'
	instead of 'c_print_type_base'.
	(print_spaces_filtered_with_print_options): New function.
	(output_access_specifier): Take new argument FLAGS.  Modify
	function to call 'print_spaces_filtered_with_print_options'.
	(c_print_type_vtable_offset_marker): New function.
	(c_print_type_union_field_offset): New function.
	(c_print_type_struct_field_offset): New function.
	(c_type_print_base_struct_union): New argument 'struct
	print_offset_data *'.  Print offsets and sizes for
	struct/union/class fields.
	* typeprint.c (const struct type_print_options
	type_print_raw_options): Initialize 'print_offsets'.
	(static struct type_print_options default_ptype_flags):
	Likewise.
	(struct print_offset_data print_offset_default_data): New
	variable.
	(whatis_exp): Handle '/o' option.
	(_initialize_typeprint): Add '/o' flag to ptype's help.
	* typeprint.h (struct print_offset_data): New struct.
	(struct type_print_options) <print_offsets>: New field.

gdb/testsuite/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR cli/16224
	* gdb.base/ptype-offsets.cc: New file.
	* gdb.base/ptype-offsets.exp: New file.

gdb/doc/ChangeLog:
yyyy-mm-dd  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR cli/16224
	* gdb.texinfo (ptype): Add documentation for new flag '/o'.
---
 gdb/NEWS                                 |   3 +
 gdb/c-typeprint.c                        | 388 +++++++++++++++++++++++++------
 gdb/doc/gdb.texinfo                      | 124 ++++++++++
 gdb/testsuite/gdb.base/ptype-offsets.cc  | 193 +++++++++++++++
 gdb/testsuite/gdb.base/ptype-offsets.exp | 317 +++++++++++++++++++++++++
 gdb/typeprint.c                          |  23 +-
 gdb/typeprint.h                          |  17 ++
 7 files changed, 999 insertions(+), 66 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/ptype-offsets.cc
 create mode 100644 gdb/testsuite/gdb.base/ptype-offsets.exp

Comments

Pedro Alves Dec. 15, 2017, 5:23 p.m. UTC | #1
Hi Sergio,

I found a couple more nits to pick, but this is close.

This is OK with the issues below addressed.  Please address
them, and push this in.  Please post the end result for the
archives.

On 12/15/2017 01:12 AM, Sergio Durigan Junior wrote:

> @@ -867,15 +913,121 @@ output_access_specifier (struct ui_file *stream,
>        if (last_access != s_public)
>  	{
>  	  last_access = s_public;
> -	  fprintfi_filtered (level + 2, stream,
> -			     "public:\n");
> +	  print_spaces_filtered_with_print_options (level + 2, stream, flags);
> +	  fprintf_filtered (stream, "public:\n");
>  	}
>      }
>  
>    return last_access;
>  }
>  
> -/* Return true is an access label (i.e., "public:", "private:",
> +/* Print information about field at index FIELD_IDX of the union type
> +   TYPE.  Since union fields don't have the concept of offsets, we
> +   just print their sizes.
> +
> +   The output is strongly based on pahole(1).  */
> +
> +static void
> +c_print_type_union_field_offset (struct type *type, unsigned int field_idx,
> +				 struct ui_file *stream)
> +{
> +  struct type *ftype = check_typedef (TYPE_FIELD_TYPE (type, field_idx));
> +
> +  fprintf_filtered (stream, "/*              %4u */", TYPE_LENGTH (ftype));
> +}
> +
> +/* Print information about field at index FIELD_IDX of the struct type
> +   TYPE.
> +
> +   END_BITPOS is the one-past-the-end bit position of the previous
> +   field (where we expect this field to be if there is no hole).  At
> +   the end, ENDPOS is updated to the one-past-the-end bit position of
> +   the current field.

There's still a reference to ENDPOS above that I assume should
be END_BITPOS.  Now that I'm looking at this, do we still need
this parameter, given print_offset_data->end_bitpos exists?
What's the relationship between the two?  It's a bit confusing
to have two things for the same.  I think the comment could/should
clarify this.

> +
> +   OFFSET_BITPOS is the offset value we carry over when we are
> +   printing a struct that is inside another struct; this is useful so
> +   that the offset is constantly incremented (if we didn't carry it
> +   over, the offset would be reset to zero when printing the inner
> +   struct).

This parameter no longer exists (it's a field of print_offset_data now,
right?).  The comment should be adjusted, moved elsewhere, or deleted.

> +
> +   The output is strongly based on pahole(1).  */
> +
> +static void
> +c_print_type_struct_field_offset (struct type *type, unsigned int field_idx,
> +				  struct ui_file *stream,
> +				  unsigned int *end_bitpos,
> +				  struct print_offset_data *podata)
> +{


> @@ -1143,9 +1347,16 @@ c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
>  		       && !is_full_physname_constructor  /* " " */
>  		       && !is_type_conversion_operator (type, i, j))
>  		{
> -		  c_print_type (TYPE_TARGET_TYPE (TYPE_FN_FIELD_TYPE (f, j)),
> -				"", stream, -1, 0,
> -				&local_flags);
> +		  unsigned int old_po = local_flags.print_offsets;
> +
> +		  /* Temporarily disable print_offsets, because it
> +		     would mess with indentation.  */
> +		  local_flags.print_offsets = 0;
> +		  c_print_type_1 (TYPE_TARGET_TYPE (TYPE_FN_FIELD_TYPE (f, j)),
> +				  "", stream, -1, 0,
> +				  &local_flags, podata);
> +		  local_flags.print_offsets = old_po;

This pattern appears in several places.  Would it make sense to
add a c_print_type_no_offsets routine that handled the
print_offsets save/restore?

> +++ b/gdb/testsuite/gdb.base/ptype-offsets.exp
> @@ -0,0 +1,317 @@
> +# This testcase is part of GDB, the GNU debugger.
> +
> +# Copyright 2017 Free Software Foundation, Inc.
> +
> +# 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/>.
> +
> +# This testcase exercises the "ptype /o" feature, which can be used to
> +# print the offsets and sizes of each field of a struct/union/class.
> +
> +standard_testfile .cc
> +
> +# Test only works on LP64 targets.  That's how we guarantee that the
> +# expected holes will be present in the struct.
> +if { ![is_lp64_target] } {
> +    untested "test work only on lp64 targets"
> +    return 0
> +}
> +
> +if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
> +	  { debug c++ }] } {
> +    return -1
> +}
> +
> +# Test general offset printing, ctor/dtor printing, union, formatting.
> +gdb_test "ptype /o struct abc" \
> +    [multi_line \

...

> +{                         \}}] \
> +    "ptype offset struct abc"

I notice that you're replacing the "/o" in most test
names/messages.  Is there a reason for that?  Why
not just let the test name default to the command
invocation?  I.e., remove the 3rd argument in all
these calls to gdb_test.


> +
> +# Test "ptype /oTM".
> +gdb_test "ptype /oTM struct abc" \
> +    [multi_line \

..

> +    "ptype /oTM struct abc"

Here the "/" persisted, so I'm curious why the other cases
have "/o" replaced by "offset".

I'd just remove the explicit test messages.  It just seems
like potential for getting out of sync otherwise.

> +# Because dealing with bitfields and offsets is difficult, it can be
> +# tricky to confirm that the output of the this command is accurate.

typo: "of the this"

> @@ -499,6 +514,11 @@ whatis_exp (const char *exp, int show)
>  	real_type = value_rtti_type (val, &full, &top, &using_enc);
>      }
>  
> +  if (flags.print_offsets
> +      && (TYPE_CODE (type) == TYPE_CODE_STRUCT
> +	  || TYPE_CODE (type) == TYPE_CODE_UNION))
> +    fprintf_filtered (gdb_stdout, "/* offset    |  size */  ");

I noticed that "whatis" also prints this header:

 (top-gdb) whatis/o minimal_symbol
 /* offset    |  size */  type = minimal_symbol

I guess it shouldn't, for it's pointless.  You could either
use the "show" parameter here, or just ignore /o for whatis
where the options are parsed, further above.

And then please add a test covering that.  :-)

You'll have to use gdb_test_multiple with an anchor,
because 

   gdb_test "whatis/o minimal_symbol" \
      "type = minimal_symbol"

would match the bad output anyway.

So something like:

   set test "whatis /o minimal_symbol"
   gdb_test_multiple $test $test {
      -ex "^$test\r\ntype = minimal_symbol\r\n$gdb_prompt $" {
          pass $test
   }

As mentioned, OK with these issues addressed.  Please push and post.

Thanks,
Pedro Alves
diff mbox

Patch

diff --git a/gdb/NEWS b/gdb/NEWS
index bd5ae36dd0..3a7e704cc6 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,9 @@ 
 
 *** Changes since GDB 8.0
 
+* The 'ptype' command now accepts a '/o' flag, which prints the
+  offsets and sizes of fields in a struct, like the pahole(1) tool.
+
 * New "--readnever" command line option instructs GDB to not read each
   symbol file's symbolic debug information.  This makes startup faster
   but at the expense of not being able to perform symbolic debugging.
diff --git a/gdb/c-typeprint.c b/gdb/c-typeprint.c
index 3854886387..b977401145 100644
--- a/gdb/c-typeprint.c
+++ b/gdb/c-typeprint.c
@@ -32,6 +32,14 @@ 
 #include "cp-abi.h"
 #include "cp-support.h"
 
+/* When printing the offsets of a struct and its fields (i.e., 'ptype
+   /o'; type_print_options::print_offsets), we use this many
+   characters when printing the offset information at the beginning of
+   the line.  This is needed in order to generate the correct amount
+   of whitespaces when no offset info should be printed for a certain
+   field.  */
+#define OFFSET_SPC_LEN 23
+
 /* A list of access specifiers used for printing.  */
 
 enum access_specifier
@@ -45,12 +53,18 @@  enum access_specifier
 static void c_type_print_varspec_prefix (struct type *,
 					 struct ui_file *,
 					 int, int, int,
-					 const struct type_print_options *);
+					 const struct type_print_options *,
+					 struct print_offset_data *);
 
 /* Print "const", "volatile", or address space modifiers.  */
 static void c_type_print_modifier (struct type *,
 				   struct ui_file *,
 				   int, int);
+
+static void c_type_print_base_1 (struct type *type, struct ui_file *stream,
+				 int show, int level,
+				 const struct type_print_options *flags,
+				 struct print_offset_data *podata);
 
 
 /* A callback function for cp_canonicalize_string_full that uses
@@ -82,14 +96,15 @@  print_name_maybe_canonical (const char *name,
 
 
 
-/* LEVEL is the depth to indent lines by.  */
+/* Helper function for c_print_type.  */
 
-void
-c_print_type (struct type *type,
-	      const char *varstring,
-	      struct ui_file *stream,
-	      int show, int level,
-	      const struct type_print_options *flags)
+static void
+c_print_type_1 (struct type *type,
+		const char *varstring,
+		struct ui_file *stream,
+		int show, int level,
+		const struct type_print_options *flags,
+		struct print_offset_data *podata)
 {
   enum type_code code;
   int demangled_args;
@@ -108,7 +123,7 @@  c_print_type (struct type *type,
     }
   else
     {
-      c_type_print_base (type, stream, show, level, flags);
+      c_type_print_base_1 (type, stream, show, level, flags, podata);
       code = TYPE_CODE (type);
       if ((varstring != NULL && *varstring != '\0')
 	  /* Need a space if going to print stars or brackets;
@@ -124,7 +139,7 @@  c_print_type (struct type *type,
 	fputs_filtered (" ", stream);
       need_post_space = (varstring != NULL && strcmp (varstring, "") != 0);
       c_type_print_varspec_prefix (type, stream, show, 0, need_post_space,
-				   flags);
+				   flags, podata);
     }
 
   if (varstring != NULL)
@@ -143,6 +158,20 @@  c_print_type (struct type *type,
     }
 }
 
+/* LEVEL is the depth to indent lines by.  */
+
+void
+c_print_type (struct type *type,
+	      const char *varstring,
+	      struct ui_file *stream,
+	      int show, int level,
+	      const struct type_print_options *flags)
+{
+  struct print_offset_data podata;
+
+  c_print_type_1 (type, varstring, stream, show, level, flags, &podata);
+}
+
 /* Print a typedef using C syntax.  TYPE is the underlying type.
    NEW_SYMBOL is the symbol naming the type.  STREAM is the stream on
    which to print.  */
@@ -310,7 +339,8 @@  c_type_print_varspec_prefix (struct type *type,
 			     struct ui_file *stream,
 			     int show, int passed_a_ptr,
 			     int need_post_space,
-			     const struct type_print_options *flags)
+			     const struct type_print_options *flags,
+			     struct print_offset_data *podata)
 {
   const char *name;
 
@@ -326,40 +356,40 @@  c_type_print_varspec_prefix (struct type *type,
     {
     case TYPE_CODE_PTR:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, 1, 1, flags);
+				   stream, show, 1, 1, flags, podata);
       fprintf_filtered (stream, "*");
       c_type_print_modifier (type, stream, 1, need_post_space);
       break;
 
     case TYPE_CODE_MEMBERPTR:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, 0, 0, flags);
+				   stream, show, 0, 0, flags, podata);
       name = type_name_no_tag (TYPE_SELF_TYPE (type));
       if (name)
 	print_name_maybe_canonical (name, flags, stream);
       else
-	c_type_print_base (TYPE_SELF_TYPE (type),
-			   stream, -1, passed_a_ptr, flags);
+	c_type_print_base_1 (TYPE_SELF_TYPE (type),
+			     stream, -1, passed_a_ptr, flags, podata);
       fprintf_filtered (stream, "::*");
       break;
 
     case TYPE_CODE_METHODPTR:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, 0, 0, flags);
+				   stream, show, 0, 0, flags, podata);
       fprintf_filtered (stream, "(");
       name = type_name_no_tag (TYPE_SELF_TYPE (type));
       if (name)
 	print_name_maybe_canonical (name, flags, stream);
       else
-	c_type_print_base (TYPE_SELF_TYPE (type),
-			   stream, -1, passed_a_ptr, flags);
+	c_type_print_base_1 (TYPE_SELF_TYPE (type),
+			     stream, -1, passed_a_ptr, flags, podata);
       fprintf_filtered (stream, "::*");
       break;
 
     case TYPE_CODE_REF:
     case TYPE_CODE_RVALUE_REF:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, 1, 0, flags);
+				   stream, show, 1, 0, flags, podata);
       fprintf_filtered (stream, TYPE_CODE(type) == TYPE_CODE_REF ? "&" : "&&");
       c_type_print_modifier (type, stream, 1, need_post_space);
       break;
@@ -367,21 +397,22 @@  c_type_print_varspec_prefix (struct type *type,
     case TYPE_CODE_METHOD:
     case TYPE_CODE_FUNC:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, 0, 0, flags);
+				   stream, show, 0, 0, flags, podata);
       if (passed_a_ptr)
 	fprintf_filtered (stream, "(");
       break;
 
     case TYPE_CODE_ARRAY:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, 0, 0, flags);
+				   stream, show, 0, 0, flags, podata);
       if (passed_a_ptr)
 	fprintf_filtered (stream, "(");
       break;
 
     case TYPE_CODE_TYPEDEF:
       c_type_print_varspec_prefix (TYPE_TARGET_TYPE (type),
-				   stream, show, passed_a_ptr, 0, flags);
+				   stream, show, passed_a_ptr, 0, flags,
+				   podata);
       break;
 
     case TYPE_CODE_UNDEF:
@@ -836,21 +867,36 @@  c_type_print_template_args (const struct type_print_options *flags,
     fputs_filtered (_("] "), stream);
 }
 
+/* Use 'print_spaces_filtered', but take into consideration the
+   type_print_options FLAGS in order to determine how many whitespaces
+   will be printed.  */
+
+static void
+print_spaces_filtered_with_print_options
+  (int level, struct ui_file *stream, const struct type_print_options *flags)
+{
+  if (!flags->print_offsets)
+    print_spaces_filtered (level, stream);
+  else
+    print_spaces_filtered (level + OFFSET_SPC_LEN, stream);
+}
+
 /* Output an access specifier to STREAM, if needed.  LAST_ACCESS is the
    last access specifier output (typically returned by this function).  */
 
 static enum access_specifier
 output_access_specifier (struct ui_file *stream,
 			 enum access_specifier last_access,
-			 int level, bool is_protected, bool is_private)
+			 int level, bool is_protected, bool is_private,
+			 const struct type_print_options *flags)
 {
   if (is_protected)
     {
       if (last_access != s_protected)
 	{
 	  last_access = s_protected;
-	  fprintfi_filtered (level + 2, stream,
-			     "protected:\n");
+	  print_spaces_filtered_with_print_options (level + 2, stream, flags);
+	  fprintf_filtered (stream, "protected:\n");
 	}
     }
   else if (is_private)
@@ -858,8 +904,8 @@  output_access_specifier (struct ui_file *stream,
       if (last_access != s_private)
 	{
 	  last_access = s_private;
-	  fprintfi_filtered (level + 2, stream,
-			     "private:\n");
+	  print_spaces_filtered_with_print_options (level + 2, stream, flags);
+	  fprintf_filtered (stream, "private:\n");
 	}
     }
   else
@@ -867,15 +913,121 @@  output_access_specifier (struct ui_file *stream,
       if (last_access != s_public)
 	{
 	  last_access = s_public;
-	  fprintfi_filtered (level + 2, stream,
-			     "public:\n");
+	  print_spaces_filtered_with_print_options (level + 2, stream, flags);
+	  fprintf_filtered (stream, "public:\n");
 	}
     }
 
   return last_access;
 }
 
-/* Return true is an access label (i.e., "public:", "private:",
+/* Print information about field at index FIELD_IDX of the union type
+   TYPE.  Since union fields don't have the concept of offsets, we
+   just print their sizes.
+
+   The output is strongly based on pahole(1).  */
+
+static void
+c_print_type_union_field_offset (struct type *type, unsigned int field_idx,
+				 struct ui_file *stream)
+{
+  struct type *ftype = check_typedef (TYPE_FIELD_TYPE (type, field_idx));
+
+  fprintf_filtered (stream, "/*              %4u */", TYPE_LENGTH (ftype));
+}
+
+/* Print information about field at index FIELD_IDX of the struct type
+   TYPE.
+
+   END_BITPOS is the one-past-the-end bit position of the previous
+   field (where we expect this field to be if there is no hole).  At
+   the end, ENDPOS is updated to the one-past-the-end bit position of
+   the current field.
+
+   OFFSET_BITPOS is the offset value we carry over when we are
+   printing a struct that is inside another struct; this is useful so
+   that the offset is constantly incremented (if we didn't carry it
+   over, the offset would be reset to zero when printing the inner
+   struct).
+
+   The output is strongly based on pahole(1).  */
+
+static void
+c_print_type_struct_field_offset (struct type *type, unsigned int field_idx,
+				  struct ui_file *stream,
+				  unsigned int *end_bitpos,
+				  struct print_offset_data *podata)
+{
+  struct type *ftype = check_typedef (TYPE_FIELD_TYPE (type, field_idx));
+  unsigned int bitpos = TYPE_FIELD_BITPOS (type, field_idx);
+  unsigned int fieldsize_byte = TYPE_LENGTH (ftype);
+  unsigned int fieldsize_bit = fieldsize_byte * TARGET_CHAR_BIT;
+
+  /* We check for *END_BITPOS > 0 because there is a specific scenario
+     when *END_BITPOS can be zero and BITPOS can be > 0: when we are
+     dealing with a struct/class with a virtual method.  Because of
+     the vtable, the first field of the struct/class will have an
+     offset of sizeof (void *) (the size of the vtable).  If we do not
+     check for *END_BITPOS > 0 here, GDB will report a hole before the
+     first field, which is not accurate.  */
+  if (*end_bitpos > 0 && *end_bitpos < bitpos)
+    {
+      /* If END_BITPOS is smaller than the current type's bitpos, it
+	 means there's a hole in the struct, so we report it here.  */
+      unsigned int hole = bitpos - *end_bitpos;
+      unsigned int hole_byte = hole / TARGET_CHAR_BIT;
+      unsigned int hole_bit = hole % TARGET_CHAR_BIT;
+
+      if (hole_bit > 0)
+	fprintf_filtered (stream, "/* XXX %2u-bit hole   */\n", hole_bit);
+
+      if (hole_byte > 0)
+	fprintf_filtered (stream, "/* XXX %2u-byte hole  */\n", hole_byte);
+    }
+
+  if (TYPE_FIELD_PACKED (type, field_idx))
+    {
+      /* We're dealing with a bitfield.  Print how many bits are left
+	 to be used.  */
+      unsigned int bitsize = TYPE_FIELD_BITSIZE (type, field_idx);
+      /* The bitpos relative to the beginning of our container
+	 field.  */
+      unsigned int relative_bitpos;
+
+      /* The following was copied from
+	 value.c:value_primitive_field.  */
+      if ((bitpos % fieldsize_bit) + bitsize <= fieldsize_bit)
+	relative_bitpos = bitpos % fieldsize_bit;
+      else
+	relative_bitpos = bitpos % TARGET_CHAR_BIT;
+
+      /* This is the exact offset (in bits) of this bitfield.  */
+      unsigned int bit_offset
+	= (bitpos - relative_bitpos) + podata->offset_bitpos;
+
+      /* The position of the field, relative to the beginning of the
+	 struct, and how many bits are left to be used in this
+	 container.  */
+      fprintf_filtered (stream, "/* %4u:%2u", bit_offset / TARGET_CHAR_BIT,
+			fieldsize_bit - (relative_bitpos + bitsize));
+      fieldsize_bit = bitsize;
+    }
+  else
+    {
+      /* The position of the field, relative to the beginning of the
+	 struct.  */
+      fprintf_filtered (stream, "/* %4u",
+			(bitpos + podata->offset_bitpos) / TARGET_CHAR_BIT);
+
+      fprintf_filtered (stream, "   ");
+    }
+
+  fprintf_filtered (stream, "   |  %4u */", fieldsize_byte);
+
+  *end_bitpos = bitpos + fieldsize_bit;
+}
+
+/* Return true if an access label (i.e., "public:", "private:",
    "protected:") needs to be printed for TYPE.  */
 
 static bool
@@ -932,7 +1084,8 @@  need_access_label_p (struct type *type)
 static void
 c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 				int show, int level,
-				const struct type_print_options *flags)
+				const struct type_print_options *flags,
+				struct print_offset_data *podata)
 {
   struct type_print_options local_flags = *flags;
   struct type_print_options semi_local_flags = *flags;
@@ -1004,6 +1157,7 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
       recursively_update_typedef_hash (local_flags.local_typedefs, type);
 
       fprintf_filtered (stream, "{\n");
+
       if (TYPE_NFIELDS (type) == 0 && TYPE_NFN_FIELDS (type) == 0
 	  && TYPE_TYPEDEF_FIELD_COUNT (type) == 0)
 	{
@@ -1032,6 +1186,10 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 
       int len = TYPE_NFIELDS (type);
       vptr_fieldno = get_vptr_fieldno (type, &basetype);
+
+      unsigned int end_bitpos = podata->end_bitpos;
+      struct print_offset_data local_podata;
+
       for (int i = TYPE_N_BASECLASSES (type); i < len; i++)
 	{
 	  QUIT;
@@ -1048,18 +1206,63 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 	      section_type = output_access_specifier
 		(stream, section_type, level,
 		 TYPE_FIELD_PROTECTED (type, i),
-		 TYPE_FIELD_PRIVATE (type, i));
+		 TYPE_FIELD_PRIVATE (type, i), flags);
+	    }
+
+	  bool is_static = field_is_static (&TYPE_FIELD (type, i));
+
+	  if (flags->print_offsets)
+	    {
+	      if (!is_static)
+		{
+		  if (TYPE_CODE (type) == TYPE_CODE_STRUCT)
+		    {
+		      c_print_type_struct_field_offset
+			(type, i, stream, &end_bitpos, podata);
+		    }
+		  else if (TYPE_CODE (type) == TYPE_CODE_UNION)
+		    c_print_type_union_field_offset (type, i, stream);
+		}
+	      else
+		print_spaces_filtered (OFFSET_SPC_LEN, stream);
 	    }
 
 	  print_spaces_filtered (level + 4, stream);
-	  if (field_is_static (&TYPE_FIELD (type, i)))
+	  if (is_static)
 	    fprintf_filtered (stream, "static ");
-	  c_print_type (TYPE_FIELD_TYPE (type, i),
-			TYPE_FIELD_NAME (type, i),
-			stream, show - 1, level + 4,
-			&local_flags);
-	  if (!field_is_static (&TYPE_FIELD (type, i))
-	      && TYPE_FIELD_PACKED (type, i))
+
+	  int newshow = show - 1;
+
+	  if (flags->print_offsets
+	      && (TYPE_CODE (TYPE_FIELD_TYPE (type, i)) == TYPE_CODE_STRUCT
+		  || TYPE_CODE (TYPE_FIELD_TYPE (type, i)) == TYPE_CODE_UNION))
+	    {
+	      /* If we're printing offsets and this field's type is
+		 either a struct or an union, then we're interested in
+		 expanding it.  */
+	      ++newshow;
+
+	      /* Make sure we carry our offset when we expand the
+		 struct/union.  */
+	      local_podata.offset_bitpos
+		= podata->offset_bitpos + TYPE_FIELD_BITPOS (type, i);
+	      /* We're entering a struct/union.  Right now, END_BITPOS
+		 points right *after* the struct/union.  However, when
+		 printing the first field of this inner struct/union,
+		 the end_bitpos we're expecting is exactly at the
+		 beginning of the struct/union.  Therefore, we
+		 subtract the length of the whole struct/union.  */
+	      local_podata.end_bitpos
+		= end_bitpos
+		  - TYPE_LENGTH (TYPE_FIELD_TYPE (type, i)) * TARGET_CHAR_BIT;
+	    }
+
+	  c_print_type_1 (TYPE_FIELD_TYPE (type, i),
+			  TYPE_FIELD_NAME (type, i),
+			  stream, newshow, level + 4,
+			  &local_flags, &local_podata);
+
+	  if (!is_static && TYPE_FIELD_PACKED (type, i))
 	    {
 	      /* It is a bitfield.  This code does not attempt
 		 to look at the bitpos and reconstruct filler,
@@ -1122,9 +1325,10 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 	      section_type = output_access_specifier
 		(stream, section_type, level,
 		 TYPE_FN_FIELD_PROTECTED (f, j),
-		 TYPE_FN_FIELD_PRIVATE (f, j));
+		 TYPE_FN_FIELD_PRIVATE (f, j), flags);
 
-	      print_spaces_filtered (level + 4, stream);
+	      print_spaces_filtered_with_print_options (level + 4, stream,
+							flags);
 	      if (TYPE_FN_FIELD_VIRTUAL_P (f, j))
 		fprintf_filtered (stream, "virtual ");
 	      else if (TYPE_FN_FIELD_STATIC_P (f, j))
@@ -1143,9 +1347,16 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 		       && !is_full_physname_constructor  /* " " */
 		       && !is_type_conversion_operator (type, i, j))
 		{
-		  c_print_type (TYPE_TARGET_TYPE (TYPE_FN_FIELD_TYPE (f, j)),
-				"", stream, -1, 0,
-				&local_flags);
+		  unsigned int old_po = local_flags.print_offsets;
+
+		  /* Temporarily disable print_offsets, because it
+		     would mess with indentation.  */
+		  local_flags.print_offsets = 0;
+		  c_print_type_1 (TYPE_TARGET_TYPE (TYPE_FN_FIELD_TYPE (f, j)),
+				  "", stream, -1, 0,
+				  &local_flags, podata);
+		  local_flags.print_offsets = old_po;
+
 		  fputs_filtered (" ", stream);
 		}
 	      if (TYPE_FN_FIELD_STUB (f, j))
@@ -1226,9 +1437,17 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 
 	  for (int i = 0; i < TYPE_NESTED_TYPES_COUNT (type); ++i)
 	    {
-	      print_spaces_filtered (level + 4, stream);
-	      c_print_type (TYPE_NESTED_TYPES_FIELD_TYPE (type, i),
-			    "", stream, show, level + 4, &semi_local_flags);
+	      unsigned int old_po = semi_local_flags.print_offsets;
+
+	      /* Temporarily disable print_offsets, because it
+		 would mess with indentation.  */
+	      print_spaces_filtered_with_print_options (level + 4, stream,
+							flags);
+	      semi_local_flags.print_offsets = 0;
+	      c_print_type_1 (TYPE_NESTED_TYPES_FIELD_TYPE (type, i),
+			      "", stream, show, level + 4, &semi_local_flags,
+			      podata);
+	      semi_local_flags.print_offsets = old_po;
 	      fprintf_filtered (stream, ";\n");
 	    }
 	}
@@ -1254,22 +1473,46 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
 		  section_type = output_access_specifier
 		    (stream, section_type, level,
 		     TYPE_TYPEDEF_FIELD_PROTECTED (type, i),
-		     TYPE_TYPEDEF_FIELD_PRIVATE (type, i));
+		     TYPE_TYPEDEF_FIELD_PRIVATE (type, i), flags);
 		}
-	      print_spaces_filtered (level + 4, stream);
+	      print_spaces_filtered_with_print_options (level + 4, stream,
+							flags);
 	      fprintf_filtered (stream, "typedef ");
 
+	      unsigned int old_po = semi_local_flags.print_offsets;
+	      /* Temporarily disable print_offsets, because it
+		 would mess with indentation.  */
+	      semi_local_flags.print_offsets = 0;
+
 	      /* We want to print typedefs with substitutions
 		 from the template parameters or globally-known
 		 typedefs but not local typedefs.  */
-	      c_print_type (target,
-			    TYPE_TYPEDEF_FIELD_NAME (type, i),
-			    stream, show - 1, level + 4,
-			    &semi_local_flags);
+	      c_print_type_1 (target,
+			      TYPE_TYPEDEF_FIELD_NAME (type, i),
+			      stream, show - 1, level + 4,
+			      &semi_local_flags, podata);
+	      semi_local_flags.print_offsets = old_po;
 	      fprintf_filtered (stream, ";\n");
 	    }
 	}
 
+      if (flags->print_offsets)
+	{
+	  if (show > 0)
+	    {
+	      fputs_filtered ("\n", stream);
+	      print_spaces_filtered_with_print_options (level + 4,
+							stream,
+							flags);
+	      fprintf_filtered (stream, "/* total size (bytes): %4u */\n",
+				TYPE_LENGTH (type));
+	    }
+
+	  print_spaces_filtered (OFFSET_SPC_LEN, stream);
+	  if (level == 0)
+	    print_spaces_filtered (2, stream);
+	}
+
       fprintfi_filtered (level, stream, "}");
     }
 
@@ -1294,9 +1537,11 @@  c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
    LEVEL is the number of spaces to indent by.
    We increase it for some recursive calls.  */
 
-void
-c_type_print_base (struct type *type, struct ui_file *stream,
-		   int show, int level, const struct type_print_options *flags)
+static void
+c_type_print_base_1 (struct type *type, struct ui_file *stream,
+		     int show, int level,
+		     const struct type_print_options *flags,
+		     struct print_offset_data *podata)
 {
   int i;
   int len;
@@ -1341,8 +1586,8 @@  c_type_print_base (struct type *type, struct ui_file *stream,
       if (TYPE_TARGET_TYPE (type) == NULL)
 	type_print_unknown_return_type (stream);
       else
-	c_type_print_base (TYPE_TARGET_TYPE (type),
-			   stream, show, level, flags);
+	c_type_print_base_1 (TYPE_TARGET_TYPE (type),
+			     stream, show, level, flags, podata);
       break;
     case TYPE_CODE_ARRAY:
     case TYPE_CODE_PTR:
@@ -1350,13 +1595,14 @@  c_type_print_base (struct type *type, struct ui_file *stream,
     case TYPE_CODE_REF:
     case TYPE_CODE_RVALUE_REF:
     case TYPE_CODE_METHODPTR:
-      c_type_print_base (TYPE_TARGET_TYPE (type),
-			 stream, show, level, flags);
+      c_type_print_base_1 (TYPE_TARGET_TYPE (type),
+			   stream, show, level, flags, podata);
       break;
 
     case TYPE_CODE_STRUCT:
     case TYPE_CODE_UNION:
-      c_type_print_base_struct_union (type, stream, show, level, flags);
+      c_type_print_base_struct_union (type, stream, show, level, flags,
+				      podata);
       break;
 
     case TYPE_CODE_ENUM:
@@ -1456,10 +1702,10 @@  c_type_print_base (struct type *type, struct ui_file *stream,
 		print_spaces_filtered (level + 4, stream);
 		/* We pass "show" here and not "show - 1" to get enum types
 		   printed.  There's no other way to see them.  */
-		c_print_type (TYPE_FIELD_TYPE (type, i),
-			      TYPE_FIELD_NAME (type, i),
-			      stream, show, level + 4,
-			      &local_flags);
+		c_print_type_1 (TYPE_FIELD_TYPE (type, i),
+				TYPE_FIELD_NAME (type, i),
+				stream, show, level + 4,
+				&local_flags, podata);
 		fprintf_filtered (stream, " @%s",
 				  plongest (TYPE_FIELD_BITPOS (type, i)));
 		if (TYPE_FIELD_BITSIZE (type, i) > 1)
@@ -1518,3 +1764,15 @@  c_type_print_base (struct type *type, struct ui_file *stream,
       break;
     }
 }
+
+/* See c_type_print_base_1.  */
+
+void
+c_type_print_base (struct type *type, struct ui_file *stream,
+		   int show, int level,
+		   const struct type_print_options *flags)
+{
+  struct print_offset_data podata;
+
+  c_type_print_base_1 (type, stream, show, level, flags, &podata);
+}
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index da3ed28dfe..60ed80c363 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -17216,6 +17216,130 @@  names are substituted when printing other types.
 @item T
 Print typedefs defined in the class.  This is the default, but the flag
 exists in case you change the default with @command{set print type typedefs}.
+
+@item o
+Print the offsets and sizes of fields in a struct, similar to what the
+@command{pahole} tool does.  This option implies the @code{/tm} flags.
+
+For example, given the following declarations:
+
+@smallexample
+struct tuv
+@{
+  int a1;
+  char *a2;
+  int a3;
+@};
+
+struct xyz
+@{
+  int f1;
+  char f2;
+  void *f3;
+  struct tuv f4;
+@};
+
+union qwe
+@{
+  struct tuv fff1;
+  struct xyz fff2;
+@};
+
+struct tyu
+@{
+  int a1 : 1;
+  int a2 : 3;
+  int a3 : 23;
+  char a4 : 2;
+  int64_t a5;
+  int a6 : 5;
+  int64_t a7 : 3;
+@};
+@end smallexample
+
+Issuing a @kbd{ptype /o struct tuv} command would print:
+
+@smallexample
+(@value{GDBP}) ptype /o struct tuv
+/* offset    |  size */  type = struct tuv @{
+/*    0      |     4 */    int a1;
+/* XXX  4-byte hole  */
+/*    8      |     8 */    char *a2;
+/*   16      |     4 */    int a3;
+
+                           /* total size (bytes):   24 */
+                         @}
+@end smallexample
+
+Notice the format of the first column of comments.  There, you can
+find two parts separated by the @samp{|} character: the @emph{offset},
+which indicates where the field is located inside the struct, in
+bytes, and the @emph{size} of the field.  Another interesting line is
+the marker of a @emph{hole} in the struct, indicating that it may be
+possible to pack the struct and make it use less space by reorganizing
+its fields.
+
+It is also possible to print offsets inside an union:
+
+@smallexample
+(@value{GDBP}) ptype /o union qwe
+/* offset    |  size */  type = union qwe @{
+/*                24 */    struct tuv @{
+/*    0      |     4 */        int a1;
+/* XXX  4-byte hole  */
+/*    8      |     8 */        char *a2;
+/*   16      |     4 */        int a3;
+
+                               /* total size (bytes):   24 */
+                           @} fff1;
+/*                40 */    struct xyz @{
+/*    0      |     4 */        int f1;
+/*    4      |     1 */        char f2;
+/* XXX  3-byte hole  */
+/*    8      |     8 */        void *f3;
+/*   16      |    24 */        struct tuv @{
+/*   16      |     4 */            int a1;
+/* XXX  4-byte hole  */
+/*   24      |     8 */            char *a2;
+/*   32      |     4 */            int a3;
+
+                                   /* total size (bytes):   24 */
+                               @} f4;
+
+                               /* total size (bytes):   40 */
+                           @} fff2;
+
+                           /* total size (bytes):   40 */
+                         @}
+@end smallexample
+
+In this case, since @code{struct tuv} and @code{struct xyz} occupy the
+same space (because we are dealing with an union), the offset is not
+printed for them.  However, you can still examine the offset of each
+of these structures' fields.
+
+Another useful scenario is printing the offsets of a struct containing
+bitfields:
+
+@smallexample
+(@value{GDBP}) ptype /o struct tyu
+/* offset    |  size */  type = struct tyu @{
+/*    0:31   |     4 */    int a1 : 1;
+/*    0:28   |     4 */    int a2 : 3;
+/*    0: 5   |     4 */    int a3 : 23;
+/*    3: 3   |     1 */    signed char a4 : 2;
+/* XXX  3-bit hole   */
+/* XXX  4-byte hole  */
+/*    8      |     8 */    int64_t a5;
+/*   16:27   |     4 */    int a6 : 5;
+/*   16:56   |     8 */    int64_t a7 : 3;
+
+                           /* total size (bytes):   24 */
+                         @}
+@end smallexample
+
+Note how the offset information is now extended to also include how
+many bits are left to be used in each bitfield.
 @end table
 
 @kindex ptype
diff --git a/gdb/testsuite/gdb.base/ptype-offsets.cc b/gdb/testsuite/gdb.base/ptype-offsets.cc
new file mode 100644
index 0000000000..86735203ad
--- /dev/null
+++ b/gdb/testsuite/gdb.base/ptype-offsets.cc
@@ -0,0 +1,193 @@ 
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2017 Free Software Foundation, Inc.
+
+   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/>.  */
+
+#include <stdint.h>
+
+/* A struct with many types of fields, in order to test 'ptype
+   /o'.  */
+
+struct abc
+{
+  /* Virtual destructor.  */
+  virtual ~abc ()
+  {}
+
+  /* 8-byte address.  Because of the virtual destructor above, this
+     field's offset will be 8.  */
+  void *field1;
+
+  /* No hole here.  */
+
+  /* 4-byte int bitfield of 1-bit.  */
+  unsigned int field2 : 1;
+
+  /* 31-bit hole here.  */
+
+  /* 4-byte int.  */
+  signed int field3;
+
+  /* No hole here.  */
+
+  /* 1-byte char.  */
+  signed char field4;
+
+  /* 7-byte hole here.  */
+
+  /* 8-byte int.  */
+  uint64_t field5;
+
+  /* We just print the offset and size of a union, ignoring its
+     fields.  */
+  union
+  {
+    /* 8-byte address.  */
+    void *field6;
+
+    /* 4-byte int.  */
+    signed int field7;
+  } field8;
+
+  /* Empty constructor.  */
+  abc ()
+  {}
+
+  /* Typedef defined in-struct.  */
+  typedef int my_int_type;
+
+  my_int_type field9;
+};
+
+/* This struct will be nested inside 'struct xyz'.  */
+
+struct tuv
+{
+  signed int a1;
+
+  signed char *a2;
+
+  signed int a3;
+};
+
+/* This struct will be nested inside 'struct pqr'.  */
+
+struct xyz
+{
+  signed int f1;
+
+  signed char f2;
+
+  void *f3;
+
+  struct tuv f4;
+};
+
+/* A struct with a nested struct.  */
+
+struct pqr
+{
+  signed int ff1;
+
+  struct xyz ff2;
+
+  signed char ff3;
+};
+
+/* A union with two nested structs.  */
+
+union qwe
+{
+  struct tuv fff1;
+
+  struct xyz fff2;
+};
+
+/* A struct with an union.  */
+
+struct poi
+{
+  signed int f1;
+
+  union qwe f2;
+
+  uint16_t f3;
+
+  struct pqr f4;
+};
+
+/* A struct with bitfields.  */
+
+struct tyu
+{
+  signed int a1 : 1;
+
+  signed int a2 : 3;
+
+  signed int a3 : 23;
+
+  signed char a4 : 2;
+
+  int64_t a5;
+
+  signed int a6 : 5;
+
+  int64_t a7 : 3;
+};
+
+/* A struct with structs and unions.  */
+
+struct asd
+{
+  struct jkl
+  {
+      signed char *f1;
+      union
+      {
+	void *ff1;
+      } f2;
+      union
+      {
+	signed char *ff2;
+      } f3;
+      int f4 : 5;
+      unsigned int f5 : 1;
+      short f6;
+  } f7;
+  unsigned long f8;
+  signed char *f9;
+  int f10 : 4;
+  unsigned int f11 : 1;
+  unsigned int f12 : 1;
+  unsigned int f13 : 1;
+  unsigned int f14 : 1;
+  void *f15;
+  void *f16;
+};
+
+
+int
+main (int argc, char *argv[])
+{
+  struct abc foo;
+  struct pqr bar;
+  union qwe c;
+  struct poi d;
+  struct tyu e;
+  struct asd f;
+  uint8_t i;
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/ptype-offsets.exp b/gdb/testsuite/gdb.base/ptype-offsets.exp
new file mode 100644
index 0000000000..67fbd72d64
--- /dev/null
+++ b/gdb/testsuite/gdb.base/ptype-offsets.exp
@@ -0,0 +1,317 @@ 
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2017 Free Software Foundation, Inc.
+
+# 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/>.
+
+# This testcase exercises the "ptype /o" feature, which can be used to
+# print the offsets and sizes of each field of a struct/union/class.
+
+standard_testfile .cc
+
+# Test only works on LP64 targets.  That's how we guarantee that the
+# expected holes will be present in the struct.
+if { ![is_lp64_target] } {
+    untested "test work only on lp64 targets"
+    return 0
+}
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
+	  { debug c++ }] } {
+    return -1
+}
+
+# Test general offset printing, ctor/dtor printing, union, formatting.
+gdb_test "ptype /o struct abc" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct abc \{} \
+{                         public:} \
+{/\*    8      |     8 \*/    void \*field1;} \
+{/\*   16:31   |     4 \*/    unsigned int field2 : 1;} \
+{/\* XXX  7-bit hole   \*/} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*   20      |     4 \*/    int field3;} \
+{/\*   24      |     1 \*/    signed char field4;} \
+{/\* XXX  7-byte hole  \*/} \
+{/\*   32      |     8 \*/    uint64_t field5;} \
+{/\*   40      |     8 \*/    union \{} \
+{/\*                 8 \*/        void \*field6;} \
+{/\*                 4 \*/        int field7;} \
+{} \
+{                               /\* total size \(bytes\):    8 \*/} \
+{                           \} field8;} \
+{/\*   48      |     4 \*/    my_int_type field9;} \
+{} \
+{                           /\* total size \(bytes\):   56 \*/} \
+{                         \}}] \
+    "ptype offset struct abc"
+
+# Test "ptype /oTM".
+gdb_test "ptype /oTM struct abc" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct abc \{} \
+{                         public:} \
+{/\*    8      |     8 \*/    void \*field1;} \
+{/\*   16:31   |     4 \*/    unsigned int field2 : 1;} \
+{/\* XXX  7-bit hole   \*/} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*   20      |     4 \*/    int field3;} \
+{/\*   24      |     1 \*/    signed char field4;} \
+{/\* XXX  7-byte hole  \*/} \
+{/\*   32      |     8 \*/    uint64_t field5;} \
+{/\*   40      |     8 \*/    union \{} \
+{/\*                 8 \*/        void \*field6;} \
+{/\*                 4 \*/        int field7;} \
+{} \
+{                               /\* total size \(bytes\):    8 \*/} \
+{                           \} field8;} \
+{/\*   48      |     4 \*/    my_int_type field9;} \
+{} \
+{                           abc\(void\);} \
+{                           ~abc\(\);} \
+{} \
+{                           typedef int my_int_type;} \
+{} \
+{                           /\* total size \(bytes\):   56 \*/} \
+{                         \}}] \
+    "ptype /oTM struct abc"
+
+# Test "ptype /TMo".  This should be the same as "ptype /o".
+gdb_test "ptype /TMo struct abc" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct abc \{} \
+{                         public:} \
+{/\*    8      |     8 \*/    void \*field1;} \
+{/\*   16:31   |     4 \*/    unsigned int field2 : 1;} \
+{/\* XXX  7-bit hole   \*/} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*   20      |     4 \*/    int field3;} \
+{/\*   24      |     1 \*/    signed char field4;} \
+{/\* XXX  7-byte hole  \*/} \
+{/\*   32      |     8 \*/    uint64_t field5;} \
+{/\*   40      |     8 \*/    union \{} \
+{/\*                 8 \*/        void \*field6;} \
+{/\*                 4 \*/        int field7;} \
+{} \
+{                               /\* total size \(bytes\):    8 \*/} \
+{                           \} field8;} \
+{/\*   48      |     4 \*/    my_int_type field9;} \
+{} \
+{                           /\* total size \(bytes\):   56 \*/} \
+{                         \}}] \
+    "ptype /TMo struct abc"
+
+# Test nested structs.
+gdb_test "ptype /o struct pqr" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct pqr \{} \
+{/\*    0      |     4 \*/    int ff1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*    8      |    40 \*/    struct xyz \{} \
+{/\*    8      |     4 \*/        int f1;} \
+{/\*   12      |     1 \*/        signed char f2;} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*   16      |     8 \*/        void \*f3;} \
+{/\*   24      |    24 \*/        struct tuv \{} \
+{/\*   24      |     4 \*/            int a1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*   32      |     8 \*/            signed char \*a2;} \
+{/\*   40      |     4 \*/            int a3;} \
+{} \
+{                                   /\* total size \(bytes\):   24 \*/} \
+{                               \} f4;} \
+{} \
+{                               /\* total size \(bytes\):   40 \*/} \
+{                           \} ff2;} \
+{/\* XXX 28-byte hole  \*/} \
+{/\*   72      |     1 \*/    signed char ff3;} \
+{} \
+{                           /\* total size \(bytes\):   56 \*/} \
+{                         \}}] \
+    "ptype offset struct pqr"
+
+# Test that the offset is properly reset when we are printing a union
+# and go inside two inner structs.
+# This also tests a struct inside a struct inside a union.
+gdb_test "ptype /o union qwe" \
+    [multi_line \
+{/\* offset    |  size \*/  type = union qwe \{} \
+{/\*                24 \*/    struct tuv \{} \
+{/\*    0      |     4 \*/        int a1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*    8      |     8 \*/        signed char \*a2;} \
+{/\*   16      |     4 \*/        int a3;} \
+{} \
+{                               /\* total size \(bytes\):   24 \*/} \
+{                           \} fff1;} \
+{/\*                40 \*/    struct xyz \{} \
+{/\*    0      |     4 \*/        int f1;} \
+{/\*    4      |     1 \*/        signed char f2;} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*    8      |     8 \*/        void \*f3;} \
+{/\*   16      |    24 \*/        struct tuv \{} \
+{/\*   16      |     4 \*/            int a1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*   24      |     8 \*/            signed char \*a2;} \
+{/\*   32      |     4 \*/            int a3;} \
+{} \
+{                                   /\* total size \(bytes\):   24 \*/} \
+{                               \} f4;} \
+{} \
+{                               /\* total size \(bytes\):   40 \*/} \
+{                           \} fff2;} \
+{} \
+{                           /\* total size \(bytes\):   40 \*/} \
+{                         \}}] \
+    "ptype offset union qwe"
+
+# Test printing a struct that contains a union, and that also
+# contains a struct.
+gdb_test "ptype /o struct poi" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct poi \{} \
+{/\*    0      |     4 \*/    int f1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*    8      |    40 \*/    union qwe \{} \
+{/\*                24 \*/        struct tuv \{} \
+{/\*    8      |     4 \*/            int a1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*   16      |     8 \*/            signed char \*a2;} \
+{/\*   24      |     4 \*/            int a3;} \
+{} \
+{                                   /\* total size \(bytes\):   24 \*/} \
+{                               \} fff1;} \
+{/\*                40 \*/        struct xyz \{} \
+{/\*    8      |     4 \*/            int f1;} \
+{/\*   12      |     1 \*/            signed char f2;} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*   16      |     8 \*/            void \*f3;} \
+{/\*   24      |    24 \*/            struct tuv \{} \
+{/\*   24      |     4 \*/                int a1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*   32      |     8 \*/                signed char \*a2;} \
+{/\*   40      |     4 \*/                int a3;} \
+{} \
+{                                       /\* total size \(bytes\):   24 \*/} \
+{                                   \} f4;} \
+{} \
+{                                   /\* total size \(bytes\):   40 \*/} \
+{                               \} fff2;} \
+{} \
+{                               /\* total size \(bytes\):   40 \*/} \
+{                           \} f2;} \
+{/\*   72      |     2 \*/    uint16_t f3;} \
+{/\* XXX  6-byte hole  \*/} \
+{/\*   80      |    56 \*/    struct pqr \{} \
+{/\*   80      |     4 \*/        int ff1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*   88      |    40 \*/        struct xyz \{} \
+{/\*   88      |     4 \*/            int f1;} \
+{/\*   92      |     1 \*/            signed char f2;} \
+{/\* XXX  3-byte hole  \*/} \
+{/\*   96      |     8 \*/            void \*f3;} \
+{/\*  104      |    24 \*/            struct tuv \{} \
+{/\*  104      |     4 \*/                int a1;} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*  112      |     8 \*/                signed char \*a2;} \
+{/\*  120      |     4 \*/                int a3;} \
+{} \
+{                                       /\* total size \(bytes\):   24 \*/} \
+{                                   \} f4;} \
+{} \
+{                                   /\* total size \(bytes\):   40 \*/} \
+{                               \} ff2;} \
+{/\*  152      |     1 \*/        signed char ff3;} \
+{} \
+{                               /\* total size \(bytes\):   56 \*/} \
+{                           \} f4;} \
+{} \
+{                           /\* total size \(bytes\):  112 \*/} \
+{                         \}}] \
+    "ptype offset struct poi"
+
+# Test printing a struct with several bitfields, laid out in various
+# ways.
+#
+# Because dealing with bitfields and offsets is difficult, it can be
+# tricky to confirm that the output of the this command is accurate.
+# A nice way to do that is to use GDB's "x" command and print the
+# actual memory layout of the struct.  In order to differentiate
+# between bitfields and non-bitfield variables, one can assign "-1" to
+# every bitfield in the struct.  An example of the output of "x" using
+# "struct tyu" is:
+#
+#   (gdb) x/24xb &e
+#   0x7fffffffd540: 0xff    0xff    0xff    0x1f    0x00    0x00    0x00    0x00
+#   0x7fffffffd548: 0xff    0xff    0xff    0xff    0xff    0xff    0xff    0xff
+#   0x7fffffffd550: 0xff    0x00    0x00    0x00    0x00    0x00    0x00    0x00
+gdb_test "ptype /o struct tyu" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct tyu \{} \
+{/\*    0:31   |     4 \*/    int a1 : 1;} \
+{/\*    0:28   |     4 \*/    int a2 : 3;} \
+{/\*    0: 5   |     4 \*/    int a3 : 23;} \
+{/\*    3: 3   |     1 \*/    signed char a4 : 2;} \
+{/\* XXX  3-bit hole   \*/} \
+{/\* XXX  4-byte hole  \*/} \
+{/\*    8      |     8 \*/    int64_t a5;} \
+{/\*   16:27   |     4 \*/    int a6 : 5;} \
+{/\*   16:56   |     8 \*/    int64_t a7 : 3;} \
+{} \
+{                           /\* total size \(bytes\):   24 \*/} \
+{                         \}}] \
+    "ptype offset struct tyu"
+
+gdb_test "ptype /o struct asd" \
+    [multi_line \
+{/\* offset    |  size \*/  type = struct asd \{} \
+{/\*    0      |    32 \*/    struct asd::jkl \{} \
+{/\*    0      |     8 \*/        signed char \*f1;} \
+{/\*    8      |     8 \*/        union \{} \
+{/\*                 8 \*/            void \*ff1;} \
+{} \
+{                                   /\* total size \(bytes\):    8 \*/} \
+{                               \} f2;} \
+{/\*   16      |     8 \*/        union \{} \
+{/\*                 8 \*/            signed char \*ff2;} \
+{} \
+{                                   /\* total size \(bytes\):    8 \*/} \
+{                               \} f3;} \
+{/\*   24:27   |     4 \*/        int f4 : 5;} \
+{/\*   24:26   |     4 \*/        unsigned int f5 : 1;} \
+{/\* XXX  2-bit hole   \*/} \
+{/\* XXX  1-byte hole  \*/} \
+{/\*   26      |     2 \*/        short f6;} \
+{} \
+{                               /\* total size \(bytes\):   32 \*/} \
+{                           \} f7;} \
+{/\*   32      |     8 \*/    unsigned long f8;} \
+{/\*   40      |     8 \*/    signed char \*f9;} \
+{/\*   48:28   |     4 \*/    int f10 : 4;} \
+{/\*   48:27   |     4 \*/    unsigned int f11 : 1;} \
+{/\*   48:26   |     4 \*/    unsigned int f12 : 1;} \
+{/\*   48:25   |     4 \*/    unsigned int f13 : 1;} \
+{/\*   48:24   |     4 \*/    unsigned int f14 : 1;} \
+{/\* XXX  7-byte hole  \*/} \
+{/\*   56      |     8 \*/    void \*f15;} \
+{/\*   64      |     8 \*/    void \*f16;} \
+{} \
+{                           /\* total size \(bytes\):   72 \*/} \
+{                         \}}] \
+    "ptype offset struct asd"
+
+# Test that we don't print any header when issuing a "ptype /o" on a
+# non-struct, non-union, non-class type.
+gdb_test "ptype /o int" "int" "ptype offset int"
+gdb_test "ptype /o uint8_t" "char" "ptype offset uint8_t"
diff --git a/gdb/typeprint.c b/gdb/typeprint.c
index 9d9d6f5a49..9f44f3329a 100644
--- a/gdb/typeprint.c
+++ b/gdb/typeprint.c
@@ -42,6 +42,7 @@  const struct type_print_options type_print_raw_options =
   1,				/* raw */
   1,				/* print_methods */
   1,				/* print_typedefs */
+  0,				/* print_offsets */
   0,				/* print_nested_type_limit  */
   NULL,				/* local_typedefs */
   NULL,				/* global_table */
@@ -55,6 +56,7 @@  static struct type_print_options default_ptype_flags =
   0,				/* raw */
   1,				/* print_methods */
   1,				/* print_typedefs */
+  0,				/* print_offsets */
   0,				/* print_nested_type_limit  */
   NULL,				/* local_typedefs */
   NULL,				/* global_table */
@@ -440,6 +442,19 @@  whatis_exp (const char *exp, int show)
 		case 'T':
 		  flags.print_typedefs = 1;
 		  break;
+		case 'o':
+		  {
+		    /* Filter out languages which don't implement the
+		       feature.  */
+		    if (current_language->la_language == language_c
+			|| current_language->la_language == language_cplus)
+		      {
+			flags.print_offsets = 1;
+			flags.print_typedefs = 0;
+			flags.print_methods = 0;
+		      }
+		    break;
+		  }
 		default:
 		  error (_("unrecognized flag '%c'"), *exp);
 		}
@@ -499,6 +514,11 @@  whatis_exp (const char *exp, int show)
 	real_type = value_rtti_type (val, &full, &top, &using_enc);
     }
 
+  if (flags.print_offsets
+      && (TYPE_CODE (type) == TYPE_CODE_STRUCT
+	  || TYPE_CODE (type) == TYPE_CODE_UNION))
+    fprintf_filtered (gdb_stdout, "/* offset    |  size */  ");
+
   printf_filtered ("type = ");
 
   if (!flags.raw)
@@ -759,7 +779,8 @@  Available FLAGS are:\n\
   /m    do not print methods defined in a class\n\
   /M    print methods defined in a class\n\
   /t    do not print typedefs defined in a class\n\
-  /T    print typedefs defined in a class"));
+  /T    print typedefs defined in a class\n\
+  /o    print offsets and sizes of fields in a struct (like pahole)\n"));
   set_cmd_completer (c, expression_completer);
 
   c = add_com ("whatis", class_vars, whatis_command,
diff --git a/gdb/typeprint.h b/gdb/typeprint.h
index a2058b0120..2e19006f22 100644
--- a/gdb/typeprint.h
+++ b/gdb/typeprint.h
@@ -24,6 +24,20 @@  struct ui_file;
 struct typedef_hash_table;
 struct ext_lang_type_printers;
 
+struct print_offset_data
+{
+  /* The offset to be applied to bitpos when PRINT_OFFSETS is true.
+     This is needed for when we are printing nested structs and want
+     to make sure that the printed offset for each field carries over
+     the offset of the outter struct.  */
+  unsigned int offset_bitpos = 0;
+
+  /* END_BITPOS is the one-past-the-end bit position of the previous
+     field (where we expect the current field to be if there is no
+     hole).  */
+  unsigned int end_bitpos = 0;
+};
+
 struct type_print_options
 {
   /* True means that no special printing flags should apply.  */
@@ -35,6 +49,9 @@  struct type_print_options
   /* True means print typedefs in a class.  */
   unsigned int print_typedefs : 1;
 
+  /* True means to print offsets, a la 'pahole'.  */
+  unsigned int print_offsets : 1;
+
   /* The number of nested type definitions to print.  -1 == all.  */
   int print_nested_type_limit;