[PATCH 8/9] Respect piece offset for DW_OP_bit_piece

Andreas Arnez
2017-04-07T17:44:34Z

So far GDB ignores the piece offset of all kinds of DWARF bit
pieces (DW_OP_bit_piece) and treats such pieces as if the offset was zero.

This is fixed, and an appropriate test is added.

gdb/ChangeLog:

* dwarf2loc.c (read_pieced_value): Respect the piece offset, as
given by DW_OP_bit_piece.
(write_pieced_value): Likewise.

Andreas Arnez <arnez@linux.vnet.ibm.com>

* gdb.dwarf2/var-access.exp: Add test for composite location with
nonzero piece offsets.
---
gdb/dwarf2loc.c | 22 ++++++++++++++------
gdb/testsuite/gdb.dwarf2/var-access.exp | 37 +++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+), 6 deletions(-)

diff --git a/gdb/dwarf2loc.c b/gdb/dwarf2loc.c
index 67df598..045c2d3 100644
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -1824,11 +1824,13 @@ read_pieced_value (struct value *v)
int optim, unavail;

if (gdbarch_byte_order (arch) == BFD_ENDIAN_BIG
- && p->size < reg_bits)
+ && p->offset + p->size < reg_bits)
{
/* Big-endian, and we want less than full size. */
- source_offset_bits += reg_bits - p->size;
+ source_offset_bits += reg_bits - (p->offset + p->size);
}
+ else
+ source_offset_bits += p->offset;
this_size = bits_to_bytes (source_offset_bits, this_size_bits);
buffer.reserve (this_size);

@@ -1850,6 +1852,7 @@ read_pieced_value (struct value *v)
break;

case DWARF_VALUE_MEMORY:
+ source_offset_bits += p->offset;
this_size = bits_to_bytes (source_offset_bits, this_size_bits);
buffer.reserve (this_size);

@@ -1869,12 +1872,14 @@ read_pieced_value (struct value *v)
ULONGEST obj_size = 8 * TYPE_LENGTH (value_type (p->v.value));

/* Use zeroes if piece reaches beyond stack value. */
- if (p->size > obj_size)
+ if (p->offset + p->size > obj_size)
break;

/* Piece is anchored at least significant bit end. */
if (gdbarch_byte_order (objfile_gdbarch) == BFD_ENDIAN_BIG)
- source_offset_bits += obj_size - p->size;
+ source_offset_bits += obj_size - (p->offset + p->size);
+ else
+ source_offset_bits += p->offset;
copy_bitwise (contents, dest_offset_bits,
value_contents_all (p->v.value),
source_offset_bits,
@@ -1888,6 +1893,7 @@ read_pieced_value (struct value *v)
size_t n = this_size_bits;

/* Cut off at the end of the implicit value. */
+ source_offset_bits += p->offset;
if (source_offset_bits >= obj_size)
break;
if (n > obj_size - source_offset_bits)
@@ -1978,11 +1984,13 @@ write_pieced_value (struct value *to, struct value *from)
ULONGEST reg_bits = 8 * register_size (arch, gdb_regnum);

if (gdbarch_byte_order (arch) == BFD_ENDIAN_BIG
- && p->size <= reg_bits)
+ && p->offset + p->size < reg_bits)
{
/* Big-endian, and we want less than full size. */
- dest_offset_bits += reg_bits - p->size;
+ dest_offset_bits += reg_bits - (p->offset + p->size);
}
+ else
+ dest_offset_bits += p->offset;
this_size = bits_to_bytes (dest_offset_bits, this_size_bits);
buffer.reserve (this_size);

@@ -2019,6 +2027,8 @@ write_pieced_value (struct value *to, struct value *from)
break;
case DWARF_VALUE_MEMORY:
{
+ dest_offset_bits += p->offset;
+
CORE_ADDR start_addr = p->v.mem.addr + dest_offset_bits / 8;

if (dest_offset_bits % 8 == 0 && this_size_bits % 8 == 0
diff --git a/gdb/testsuite/gdb.dwarf2/var-access.exp b/gdb/testsuite/gdb.dwarf2/var-access.exp
index 4787dfb..29d61f8 100644
--- a/gdb/testsuite/gdb.dwarf2/var-access.exp
+++ b/gdb/testsuite/gdb.dwarf2/var-access.exp
@@ -204,6 +204,22 @@ Dwarf::assemble $asm_file {
piece 1
} SPECIAL_expr}
}
+ # One piece per bitfield. Use piece offsets.
+ DW_TAG_variable {
+ {name "t3"}
+ {type :$struct_t_label}
+ {location {
+ implicit_value 0x12 0x34 0x56 0x78 0x9a
+ bit_piece 32 4
+ const2s -280
+ stack_value
+ bit_piece 9 2
+ regx [lindex $dwarf_regnum 0]
+ bit_piece 13 14
+ addr $buf_var
+ bit_piece 10 42
+ } SPECIAL_expr}
+ }
}
}
}
@@ -276,3 +292,24 @@ gdb_test_no_output "set var t2.y = 2641"
gdb_test_no_output "set var t2.z = -400"
gdb_test_no_output "set var t2.x = 200"
gdb_test "print t2.x + t2.y + t2.z" " = 2441"
+
+# Bitfield access through pieces with nonzero piece offsets.
+gdb_test_no_output "set var \$[lindex $regname 0] = 0xa8000" \
+ "init reg for t3.y"
+gdb_test_no_output "set var *(char \[2\] *) (a + 5) = { 70, 82 }" \
+ "init mem for t3.z"
+switch $endian {
+ little {set val "u = -1484430527, x = -70, y = 42, z = 145"}
+ big {set val "u = 591751049, x = -70, y = 42, z = 101"}
+}
+gdb_test "print t3" " = \\{$val\\}" \
+ "initialized t3 from reg and mem"
+gdb_test_no_output "set var t3.y = -1" \
+ "overwrite t3.y"
+gdb_test "print/x \$[lindex $regname 0]" " = 0x7ffc000" \
+ "verify t3.y through reg"
+gdb_test_no_output "set var t3.z = -614" \
+ "overwrite t3.z"
+switch $endian {big {set val "0x59, 0xa2"} little {set val "0x6a, 0x56"}}
+gdb_test "print/x *(char \[2\] *) (a + 5)" " = \\{$val\\}" \
+ "verify t3.z through mem"
--
2.3.0