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Show padding in ptype/o output

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I was recently using ptype/o to look at the layout of some objects in
gdb.  I noticed that trailing padding was not shown -- but I wanted to
be able to look at that, too.

This patch changes ptype/o to also print trailing holes.

Tested on x86-64 Fedora 26.

gdb/ChangeLog
2018-05-18  Tom Tromey  <tom@tromey.com>

	* c-typeprint.c (maybe_print_hole): New function.
	(c_print_type_struct_field_offset): Update.
	(c_type_print_base_struct_union): Call maybe_print_hole.

gdb/testsuite/ChangeLog
2018-05-18  Tom Tromey  <tom@tromey.com>

	* gdb.base/ptype-offsets.exp: Update.
This commit is contained in:
Tom Tromey
2018-05-12 17:04:50 -06:00
parent 7b4ae82428
commit ce1e8424c6
4 changed files with 62 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

62
gdb/c-typeprint.c
View File

@ -937,6 +937,42 @@ c_print_type_union_field_offset (struct type *type, unsigned int field_idx,
fprintf_filtered (stream, "/* %4u */", TYPE_LENGTH (ftype));
}
/* Helper function for ptype/o implementation that prints information
about a hole, if necessary. STREAM is where to print. BITPOS is
the bitpos of the current field. PODATA is the offset-printing
state. FOR_WHAT is a string describing the purpose of the
hole. */
static void
maybe_print_hole (struct ui_file *stream, unsigned int bitpos,
struct print_offset_data *podata, const char *for_what)
{
/* We check for PODATA->END_BITPOS > 0 because there is a specific
scenario when PODATA->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 PODATA->END_BITPOS > 0 here, GDB will report
a hole before the first field, which is not accurate. */
if (podata->end_bitpos > 0 && podata->end_bitpos < bitpos)
{
/* If PODATA->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 - podata->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 %s */\n", hole_bit,
for_what);
if (hole_byte > 0)
fprintf_filtered (stream, "/* XXX %2u-byte %s */\n", hole_byte,
for_what);
}
}
/* Print information about field at index FIELD_IDX of the struct type
TYPE.
@ -963,28 +999,7 @@ c_print_type_struct_field_offset (struct type *type, unsigned int field_idx,
unsigned int fieldsize_byte = TYPE_LENGTH (ftype);
unsigned int fieldsize_bit = fieldsize_byte * TARGET_CHAR_BIT;
/* We check for PODATA->END_BITPOS > 0 because there is a specific
scenario when PODATA->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 PODATA->END_BITPOS > 0 here, GDB will report
a hole before the first field, which is not accurate. */
if (podata->end_bitpos > 0 && podata->end_bitpos < bitpos)
{
/* If PODATA->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 - podata->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);
}
maybe_print_hole (stream, bitpos, podata, "hole");
if (TYPE_FIELD_PACKED (type, field_idx))
{
@ -1508,6 +1523,9 @@ c_type_print_base_struct_union (struct type *type, struct ui_file *stream,
{
if (show > 0)
{
unsigned int bitpos = TYPE_LENGTH (type) * TARGET_CHAR_BIT;
maybe_print_hole (stream, bitpos, podata, "padding");
fputs_filtered ("\n", stream);
print_spaces_filtered_with_print_options (level + 4,
stream,