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Change ptype/o to print bit offset
Consider this short C example:
struct inner
{
unsigned x;
unsigned y : 3;
unsigned z : 3;
};
struct outer
{
unsigned char o : 3;
struct inner i __attribute__ ((packed));
};
When I use "ptype/o" on this, I get:
(gdb) ptype/o struct outer
/* offset | size */ type = struct outer {
/* 0: 5 | 1 */ unsigned char o : 3;
/* XXX 5-bit hole */
/* 1 | 8 */ struct inner {
/* 1 | 4 */ unsigned int x;
/* 5:29 | 4 */ unsigned int y : 3;
/* 5:26 | 4 */ unsigned int z : 3;
/* XXX 2-bit padding */
/* XXX 3-byte padding */
/* total size (bytes): 8 */
} i;
/* total size (bytes): 9 */
}
In the location of "o" ("0: 5"), the "5" means "there are 5 bits left
relative to the size of the underlying type.
I find this very difficult to follow. On irc, Sergio said that this
choice came because it is what pahole does. However, I think it's not
very useful, and maybe is just an artifact of the way that
DW_AT_bit_offset was defined in DWARF 3.
This patch changes ptype/o to print the offset of a bitfield in a more
natural way, that is, using the bit number according to the platform's
bit numbering.
With this patch, the output is now:
(gdb) ptype/o struct outer
/* offset | size */ type = struct outer {
/* 0: 0 | 1 */ unsigned char o : 3;
/* XXX 5-bit hole */
/* 1 | 8 */ struct inner {
/* 1 | 4 */ unsigned int x;
/* 5: 0 | 4 */ unsigned int y : 3;
/* 5: 3 | 4 */ unsigned int z : 3;
/* XXX 2-bit padding */
/* XXX 3-byte padding */
/* total size (bytes): 8 */
} i;
/* total size (bytes): 9 */
}
This is better, IMO, because now the "offset" of a bitfield is
consistent with the offset of an ordinary member, referring to its
offset from the start of the structure.
gdb/ChangeLog
2019-05-08 Tom Tromey <tromey@adacore.com>
* typeprint.c (print_offset_data::update): Print the bit offset,
not the number of bits remaining.
gdb/doc/ChangeLog
2019-05-08 Tom Tromey <tromey@adacore.com>
* gdb.texinfo (Symbols): Document change to ptype/o.
gdb/testsuite/ChangeLog
2019-05-08 Tom Tromey <tromey@adacore.com>
* gdb.base/ptype-offsets.exp: Update tests.
This commit is contained in:
Tom Tromey
parent
844333e249
commit
9d3421afbb
@ -1,3 +1,8 @@
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2019-05-08 Tom Tromey <tromey@adacore.com>
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* typeprint.c (print_offset_data::update): Print the bit offset,
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not the number of bits remaining.
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2019-05-08 Tom Tromey <tromey@adacore.com>
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* typeprint.c (print_offset_data::maybe_print_hole): Add extra
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@ -1,3 +1,7 @@
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2019-05-08 Tom Tromey <tromey@adacore.com>
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* gdb.texinfo (Symbols): Document change to ptype/o.
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2019-05-03 Eli Zaretskii <eliz@gnu.org>
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* gdb.texinfo (Separate Debug Files): Document how the
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@ -17861,15 +17861,16 @@ bitfields:
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/* XXX 3-bit hole */
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/* XXX 4-byte hole */
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/* 8 | 8 */ int64_t a5;
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/* 16:27 | 4 */ int a6 : 5;
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/* 16:56 | 8 */ int64_t a7 : 3;
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/* 16: 0 | 4 */ int a6 : 5;
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/* 16: 5 | 8 */ int64_t a7 : 3;
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"/* XXX 7-byte padding */
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/* total size (bytes): 24 */
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@}
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@end smallexample
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Note how the offset information is now extended to also include how
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many bits are left to be used in each bitfield.
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Note how the offset information is now extended to also include the
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first bit of the bitfield.
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@end table
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@kindex ptype
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@ -1,3 +1,7 @@
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2019-05-08 Tom Tromey <tromey@adacore.com>
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* gdb.base/ptype-offsets.exp: Update tests.
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2019-05-08 Tom Tromey <tromey@adacore.com>
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* gdb.base/ptype-offsets.exp: Use string_to_regexp. Fix test
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@ -38,7 +38,7 @@ gdb_test "ptype /o struct abc" \
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"/* offset | size */ type = struct abc \{" \
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" public:" \
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"/* 8 | 8 */ void *field1;" \
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"/* 16:31 | 4 */ unsigned int field2 : 1;" \
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"/* 16: 0 | 4 */ unsigned int field2 : 1;" \
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"/* XXX 7-bit hole */" \
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"/* XXX 3-byte hole */" \
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"/* 20 | 4 */ int field3;" \
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@ -63,7 +63,7 @@ gdb_test "ptype /oTM struct abc" \
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"/* offset | size */ type = struct abc \{" \
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" public:" \
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"/* 8 | 8 */ void *field1;" \
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"/* 16:31 | 4 */ unsigned int field2 : 1;" \
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"/* 16: 0 | 4 */ unsigned int field2 : 1;" \
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"/* XXX 7-bit hole */" \
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"/* XXX 3-byte hole */" \
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"/* 20 | 4 */ int field3;" \
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@ -93,7 +93,7 @@ gdb_test "ptype /TMo struct abc" \
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"/* offset | size */ type = struct abc \{" \
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" public:" \
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"/* 8 | 8 */ void *field1;" \
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"/* 16:31 | 4 */ unsigned int field2 : 1;" \
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"/* 16: 0 | 4 */ unsigned int field2 : 1;" \
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"/* XXX 7-bit hole */" \
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"/* XXX 3-byte hole */" \
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"/* 20 | 4 */ int field3;" \
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@ -264,15 +264,15 @@ gdb_test "ptype /o struct poi" \
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gdb_test "ptype /o struct tyu" \
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[string_to_regexp [multi_line \
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"/* offset | size */ type = struct tyu \{" \
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"/* 0:31 | 4 */ int a1 : 1;" \
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"/* 0:28 | 4 */ int a2 : 3;" \
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"/* 0: 5 | 4 */ int a3 : 23;" \
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"/* 0: 0 | 4 */ int a1 : 1;" \
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"/* 0: 1 | 4 */ int a2 : 3;" \
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"/* 0: 4 | 4 */ int a3 : 23;" \
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"/* 3: 3 | 1 */ signed char a4 : 2;" \
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"/* XXX 3-bit hole */" \
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"/* XXX 4-byte hole */" \
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"/* 8 | 8 */ int64_t a5;" \
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"/* 16:27 | 4 */ int a6 : 5;" \
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"/* 16:56 | 8 */ int64_t a7 : 3;" \
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"/* 16: 0 | 4 */ int a6 : 5;" \
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"/* 16: 5 | 8 */ int64_t a7 : 3;" \
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"/* XXX 7-byte padding */" \
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"" \
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" /* total size (bytes): 24 */" \
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@ -293,8 +293,8 @@ gdb_test "ptype /o struct asd" \
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"" \
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" /* total size (bytes): 8 */" \
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" \} f3;" \
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"/* 24:27 | 4 */ int f4 : 5;" \
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"/* 24:26 | 4 */ unsigned int f5 : 1;" \
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"/* 24: 0 | 4 */ int f4 : 5;" \
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"/* 24: 5 | 4 */ unsigned int f5 : 1;" \
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"/* XXX 2-bit hole */" \
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"/* XXX 1-byte hole */" \
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"/* 26 | 2 */ short f6;" \
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@ -304,11 +304,11 @@ gdb_test "ptype /o struct asd" \
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" \} f7;" \
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"/* 32 | 8 */ unsigned long f8;" \
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"/* 40 | 8 */ signed char *f9;" \
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"/* 48:28 | 4 */ int f10 : 4;" \
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"/* 48:27 | 4 */ unsigned int f11 : 1;" \
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"/* 48:26 | 4 */ unsigned int f12 : 1;" \
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"/* 48:25 | 4 */ unsigned int f13 : 1;" \
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"/* 48:24 | 4 */ unsigned int f14 : 1;" \
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"/* 48: 0 | 4 */ int f10 : 4;" \
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"/* 48: 4 | 4 */ unsigned int f11 : 1;" \
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"/* 48: 5 | 4 */ unsigned int f12 : 1;" \
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"/* 48: 6 | 4 */ unsigned int f13 : 1;" \
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"/* 48: 7 | 4 */ unsigned int f14 : 1;" \
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"/* XXX 7-byte hole */" \
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"/* 56 | 8 */ void *f15;" \
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"/* 64 | 8 */ void *f16;" \
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@ -131,32 +131,16 @@ print_offset_data::update (struct type *type, unsigned int field_idx,
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maybe_print_hole (stream, bitpos, "hole");
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if (TYPE_FIELD_PACKED (type, field_idx))
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if (TYPE_FIELD_PACKED (type, field_idx)
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|| offset_bitpos % TARGET_CHAR_BIT != 0)
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{
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/* We're dealing with a bitfield. Print how many bits are left
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to be used. */
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unsigned int bitsize = TYPE_FIELD_BITSIZE (type, field_idx);
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/* The bitpos relative to the beginning of our container
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field. */
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unsigned int relative_bitpos;
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/* We're dealing with a bitfield. Print the bit offset. */
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fieldsize_bit = TYPE_FIELD_BITSIZE (type, field_idx);
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/* The following was copied from
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value.c:value_primitive_field. */
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if ((bitpos % fieldsize_bit) + bitsize <= fieldsize_bit)
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relative_bitpos = bitpos % fieldsize_bit;
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else
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relative_bitpos = bitpos % TARGET_CHAR_BIT;
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unsigned real_bitpos = bitpos + offset_bitpos;
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/* This is the exact offset (in bits) of this bitfield. */
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unsigned int bit_offset
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= (bitpos - relative_bitpos) + offset_bitpos;
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/* The position of the field, relative to the beginning of the
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struct, and how many bits are left to be used in this
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container. */
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fprintf_filtered (stream, "/* %4u:%2u", bit_offset / TARGET_CHAR_BIT,
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fieldsize_bit - (relative_bitpos + bitsize));
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fieldsize_bit = bitsize;
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fprintf_filtered (stream, "/* %4u:%2u", real_bitpos / TARGET_CHAR_BIT,
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real_bitpos % TARGET_CHAR_BIT);
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}
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else
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{
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