diff options
| author | Tom Tromey <tromey@adacore.com> | 2019-04-29 09:55:56 -0600 |
|---|---|---|
| committer | Tom Tromey <tromey@adacore.com> | 2019-05-08 10:15:51 -0600 |
| commit | 9d3421afbb9f3cfc8e67366ba75ea12ed8f732a3 (patch) | |
| tree | 66eb6aba210e07f4f76b979c07687598d477dcea /gdb/doc/gdb.texinfo | |
| parent | 844333e24966817fe4d622494a75c8ae0acdb91f (diff) | |
| download | gdb-9d3421afbb9f3cfc8e67366ba75ea12ed8f732a3.zip gdb-9d3421afbb9f3cfc8e67366ba75ea12ed8f732a3.tar.gz gdb-9d3421afbb9f3cfc8e67366ba75ea12ed8f732a3.tar.bz2 | |
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.
Diffstat (limited to 'gdb/doc/gdb.texinfo')
| -rw-r--r-- | gdb/doc/gdb.texinfo | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index dd8ae91..b7f3b27 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -17861,15 +17861,16 @@ bitfields: /* 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; +/* 16: 0 | 4 */ int a6 : 5; +/* 16: 5 | 8 */ int64_t a7 : 3; +"/* XXX 7-byte padding */ /* 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. +Note how the offset information is now extended to also include the +first bit of the bitfield. @end table @kindex ptype |