From 9d3421afbb9f3cfc8e67366ba75ea12ed8f732a3 Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Mon, 29 Apr 2019 09:55:56 -0600 Subject: [PATCH] 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 * typeprint.c (print_offset_data::update): Print the bit offset, not the number of bits remaining. gdb/doc/ChangeLog 2019-05-08 Tom Tromey * gdb.texinfo (Symbols): Document change to ptype/o. gdb/testsuite/ChangeLog 2019-05-08 Tom Tromey * gdb.base/ptype-offsets.exp: Update tests. --- gdb/ChangeLog | 5 ++++ gdb/doc/ChangeLog | 4 ++++ gdb/doc/gdb.texinfo | 9 +++---- gdb/testsuite/ChangeLog | 4 ++++ gdb/testsuite/gdb.base/ptype-offsets.exp | 30 ++++++++++++------------ gdb/typeprint.c | 30 ++++++------------------ 6 files changed, 40 insertions(+), 42 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index c62998fa67..93641a06de 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2019-05-08 Tom Tromey + + * typeprint.c (print_offset_data::update): Print the bit offset, + not the number of bits remaining. + 2019-05-08 Tom Tromey * typeprint.c (print_offset_data::maybe_print_hole): Add extra diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog index a26e20c823..14c44620a6 100644 --- a/gdb/doc/ChangeLog +++ b/gdb/doc/ChangeLog @@ -1,3 +1,7 @@ +2019-05-08 Tom Tromey + + * gdb.texinfo (Symbols): Document change to ptype/o. + 2019-05-03 Eli Zaretskii * gdb.texinfo (Separate Debug Files): Document how the diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index dd8ae91b93..b7f3b271d1 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 diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index eb1110e1e0..6b51db8016 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2019-05-08 Tom Tromey + + * gdb.base/ptype-offsets.exp: Update tests. + 2019-05-08 Tom Tromey * gdb.base/ptype-offsets.exp: Use string_to_regexp. Fix test diff --git a/gdb/testsuite/gdb.base/ptype-offsets.exp b/gdb/testsuite/gdb.base/ptype-offsets.exp index 12b3a74600..6116520bbd 100644 --- a/gdb/testsuite/gdb.base/ptype-offsets.exp +++ b/gdb/testsuite/gdb.base/ptype-offsets.exp @@ -38,7 +38,7 @@ gdb_test "ptype /o struct abc" \ "/* offset | size */ type = struct abc \{" \ " public:" \ "/* 8 | 8 */ void *field1;" \ -"/* 16:31 | 4 */ unsigned int field2 : 1;" \ +"/* 16: 0 | 4 */ unsigned int field2 : 1;" \ "/* XXX 7-bit hole */" \ "/* XXX 3-byte hole */" \ "/* 20 | 4 */ int field3;" \ @@ -63,7 +63,7 @@ gdb_test "ptype /oTM struct abc" \ "/* offset | size */ type = struct abc \{" \ " public:" \ "/* 8 | 8 */ void *field1;" \ -"/* 16:31 | 4 */ unsigned int field2 : 1;" \ +"/* 16: 0 | 4 */ unsigned int field2 : 1;" \ "/* XXX 7-bit hole */" \ "/* XXX 3-byte hole */" \ "/* 20 | 4 */ int field3;" \ @@ -93,7 +93,7 @@ gdb_test "ptype /TMo struct abc" \ "/* offset | size */ type = struct abc \{" \ " public:" \ "/* 8 | 8 */ void *field1;" \ -"/* 16:31 | 4 */ unsigned int field2 : 1;" \ +"/* 16: 0 | 4 */ unsigned int field2 : 1;" \ "/* XXX 7-bit hole */" \ "/* XXX 3-byte hole */" \ "/* 20 | 4 */ int field3;" \ @@ -264,15 +264,15 @@ gdb_test "ptype /o struct poi" \ gdb_test "ptype /o struct tyu" \ [string_to_regexp [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;" \ +"/* 0: 0 | 4 */ int a1 : 1;" \ +"/* 0: 1 | 4 */ int a2 : 3;" \ +"/* 0: 4 | 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;" \ +"/* 16: 0 | 4 */ int a6 : 5;" \ +"/* 16: 5 | 8 */ int64_t a7 : 3;" \ "/* XXX 7-byte padding */" \ "" \ " /* total size (bytes): 24 */" \ @@ -293,8 +293,8 @@ gdb_test "ptype /o struct asd" \ "" \ " /* total size (bytes): 8 */" \ " \} f3;" \ -"/* 24:27 | 4 */ int f4 : 5;" \ -"/* 24:26 | 4 */ unsigned int f5 : 1;" \ +"/* 24: 0 | 4 */ int f4 : 5;" \ +"/* 24: 5 | 4 */ unsigned int f5 : 1;" \ "/* XXX 2-bit hole */" \ "/* XXX 1-byte hole */" \ "/* 26 | 2 */ short f6;" \ @@ -304,11 +304,11 @@ gdb_test "ptype /o struct asd" \ " \} 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;" \ +"/* 48: 0 | 4 */ int f10 : 4;" \ +"/* 48: 4 | 4 */ unsigned int f11 : 1;" \ +"/* 48: 5 | 4 */ unsigned int f12 : 1;" \ +"/* 48: 6 | 4 */ unsigned int f13 : 1;" \ +"/* 48: 7 | 4 */ unsigned int f14 : 1;" \ "/* XXX 7-byte hole */" \ "/* 56 | 8 */ void *f15;" \ "/* 64 | 8 */ void *f16;" \ diff --git a/gdb/typeprint.c b/gdb/typeprint.c index d1cdfe11cc..7a44dbdb31 100644 --- a/gdb/typeprint.c +++ b/gdb/typeprint.c @@ -131,32 +131,16 @@ print_offset_data::update (struct type *type, unsigned int field_idx, maybe_print_hole (stream, bitpos, "hole"); - if (TYPE_FIELD_PACKED (type, field_idx)) + if (TYPE_FIELD_PACKED (type, field_idx) + || offset_bitpos % TARGET_CHAR_BIT != 0) { - /* 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; + /* We're dealing with a bitfield. Print the bit offset. */ + fieldsize_bit = TYPE_FIELD_BITSIZE (type, field_idx); - /* This is the exact offset (in bits) of this bitfield. */ - unsigned int bit_offset - = (bitpos - relative_bitpos) + offset_bitpos; + unsigned real_bitpos = bitpos + 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; + fprintf_filtered (stream, "/* %4u:%2u", real_bitpos / TARGET_CHAR_BIT, + real_bitpos % TARGET_CHAR_BIT); } else { -- 2.34.1