Re: Regression for i686 gdb.dwarf2/pieces-optimized-out.exp [Re: [PATCH v2] Handle partially optimized out values similarly to unavailable values]

Pedro Alves
2014-08-22T16:20:45Z

On 08/21/2014 08:57 PM, Jan Kratochvil wrote:
> On Wed, 20 Aug 2014 01:36:35 +0200, Pedro Alves wrote:
>> Great, I pushed this in then.
>
> -PASS: gdb.dwarf2/pieces-optimized-out.exp: print s
> +FAIL: gdb.dwarf2/pieces-optimized-out.exp: print s
>
> for i686 and x86_64-m32 configurations on all known platforms:
>
> 9a0dc9e3699018b15980bb6a39eb33dea8fefa34 is the first bad commit
> commit 9a0dc9e3699018b15980bb6a39eb33dea8fefa34
> Author: Pedro Alves <palves@redhat.com>
> Date: Wed Aug 20 00:07:40 2014 +0100
>
> Handle partially optimized out values similarly to unavailable values
>

Thanks Jan.

So it didn't take that long to get back to handling partially
optimized out bitfields after all... I think I found an easy way.
We don't currently print partially optimized out scalars, though
we could print the valid/invalid bits with p/t, for example,
and I think the code ends up clearer anyway.

----------
Subject: [PATCH] Regression for i686 gdb.dwarf2/pieces-optimized-out.exp

Git 9a0dc9e3 regressed gdb.dwarf2/pieces-optimized-out.exp, visible on
i686 (the test doesn't run on x86_64):

(gdb) p s
-$1 = {a = 5, b = <optimized out>, c = <optimized out>, d = <optimized out>}
+$1 = {a = 5, b = <optimized out>, c = 0, d = 0}
-(gdb) PASS: gdb.dwarf2/pieces-optimized-out.exp: print s
+(gdb) FAIL: gdb.dwarf2/pieces-optimized-out.exp: print s

The regression was caused by this removal in cp-valprint.c:

@@ -293,12 +293,6 @@ cp_print_value_fields (struct type *type, struct type *real_type,
{
fputs_filtered (_("<synthetic pointer>"), stream);
}
- else if (!value_bits_valid (val,
- TYPE_FIELD_BITPOS (type, i),
- TYPE_FIELD_BITSIZE (type, i)))
- {
- val_print_optimized_out (val, stream);
- }
else
{
struct value_print_options opts = *options;

The idea was that we'd just fallback to calling value_field_bitfield,
which handles unavailable values (in unpack_value_bits_as_long_1) so
should be able to handle optimized out values too. Alas, it doesn't.
This is currently a bit too messy. Instead of teaching
unpack_value_bits_as_long_1 about optimized out bits, let's bite the
bullet and teach the value code to handle partially optimized out
bitfield, by having it unpack a bitfield and then propagate the range
metadata. Turns out the resulting code looks simpler and clearer.

Tested on x86_64 Fedora 20, -m64/-m32.

gdb/ChangeLog:
2014-08-22 Pedro Alves <palves@redhat.com>

* value.c (value_ranges_copy_adjusted): New function, factored out
from ...
(value_contents_copy_raw): ... here.
(unpack_value_bits_as_long_1): Rename back to ...
(unpack_bits_as_long): ... this. Remove 'original_value' and
'result' parameters. Change return type to LONGEST.
(unpack_value_bits_as_long): Delete.
(unpack_value_field_as_long_1): Delete.
(unpack_value_field_as_long, unpack_field_as_long): Reimplement.
(unpack_value_bitfield): New function.
(value_field_bitfield): Reimplement using unpack_value_bitfield.
(value_fetch_lazy): Use unpack_value_bitfield.
* value.h (unpack_value_bits_as_long): Delete declaration.
---
gdb/value.c | 227 +++++++++++++++++++++++++++++-------------------------------
gdb/value.h | 7 --
2 files changed, 109 insertions(+), 125 deletions(-)

diff --git a/gdb/value.c b/gdb/value.c
index 077d234..6620f96 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1219,6 +1219,22 @@ ranges_copy_adjusted (VEC (range_s) **dst_range, int dst_bit_offset,
}
}

+/* Copy the ranges metadata in SRC that overlaps [SRC_BIT_OFFSET,
+ SRC_BIT_OFFSET+BIT_LENGTH) into DST, adjusted. */
+
+static void
+value_ranges_copy_adjusted (struct value *dst, int dst_bit_offset,
+ const struct value *src, int src_bit_offset,
+ int bit_length)
+{
+ ranges_copy_adjusted (&dst->unavailable, dst_bit_offset,
+ src->unavailable, src_bit_offset,
+ bit_length);
+ ranges_copy_adjusted (&dst->optimized_out, dst_bit_offset,
+ src->optimized_out, src_bit_offset,
+ bit_length);
+}
+
/* Copy LENGTH bytes of SRC value's (all) contents
(value_contents_all) starting at SRC_OFFSET, into DST value's (all)
contents, starting at DST_OFFSET. If unavailable contents are
@@ -1261,13 +1277,9 @@ value_contents_copy_raw (struct value *dst, int dst_offset,
dst_bit_offset = dst_offset * TARGET_CHAR_BIT;
bit_length = length * TARGET_CHAR_BIT;

- ranges_copy_adjusted (&dst->unavailable, dst_bit_offset,
- src->unavailable, src_bit_offset,
- bit_length);
-
- ranges_copy_adjusted (&dst->optimized_out, dst_bit_offset,
- src->optimized_out, src_bit_offset,
- bit_length);
+ value_ranges_copy_adjusted (dst, dst_bit_offset,
+ src, src_bit_offset,
+ bit_length);
}

/* Copy LENGTH bytes of SRC value's (all) contents
@@ -3105,16 +3117,24 @@ value_fn_field (struct value **arg1p, struct fn_field *f,

\f

-/* Helper function for both unpack_value_bits_as_long and
- unpack_bits_as_long. See those functions for more details on the
- interface; the only difference is that this function accepts either
- a NULL or a non-NULL ORIGINAL_VALUE. */
+/* Unpack a bitfield of the specified FIELD_TYPE, from the object at
+ VALADDR, and store the result in *RESULT.
+ The bitfield starts at BITPOS bits and contains BITSIZE bits.

-static int
-unpack_value_bits_as_long_1 (struct type *field_type, const gdb_byte *valaddr,
- int embedded_offset, int bitpos, int bitsize,
- const struct value *original_value,
- LONGEST *result)
+ Extracting bits depends on endianness of the machine. Compute the
+ number of least significant bits to discard. For big endian machines,
+ we compute the total number of bits in the anonymous object, subtract
+ off the bit count from the MSB of the object to the MSB of the
+ bitfield, then the size of the bitfield, which leaves the LSB discard
+ count. For little endian machines, the discard count is simply the
+ number of bits from the LSB of the anonymous object to the LSB of the
+ bitfield.
+
+ If the field is signed, we also do sign extension. */
+
+static LONGEST
+unpack_bits_as_long (struct type *field_type, const gdb_byte *valaddr,
+ int bitpos, int bitsize)
{
enum bfd_endian byte_order = gdbarch_byte_order (get_type_arch (field_type));
ULONGEST val;
@@ -3133,12 +3153,7 @@ unpack_value_bits_as_long_1 (struct type *field_type, const gdb_byte *valaddr,

read_offset = bitpos / 8;

- if (original_value != NULL
- && !value_bits_available (original_value, embedded_offset + bitpos,
- bitsize))
- return 0;
-
- val = extract_unsigned_integer (valaddr + embedded_offset + read_offset,
+ val = extract_unsigned_integer (valaddr + read_offset,
bytes_read, byte_order);

/* Extract bits. See comment above. */
@@ -3165,60 +3180,7 @@ unpack_value_bits_as_long_1 (struct type *field_type, const gdb_byte *valaddr,
}
}

- *result = val;
- return 1;
-}
-
-/* Unpack a bitfield of the specified FIELD_TYPE, from the object at
- VALADDR + EMBEDDED_OFFSET, and store the result in *RESULT.
- VALADDR points to the contents of ORIGINAL_VALUE, which must not be
- NULL. The bitfield starts at BITPOS bits and contains BITSIZE
- bits.
-
- Returns false if the value contents are unavailable, otherwise
- returns true, indicating a valid value has been stored in *RESULT.
-
- Extracting bits depends on endianness of the machine. Compute the
- number of least significant bits to discard. For big endian machines,
- we compute the total number of bits in the anonymous object, subtract
- off the bit count from the MSB of the object to the MSB of the
- bitfield, then the size of the bitfield, which leaves the LSB discard
- count. For little endian machines, the discard count is simply the
- number of bits from the LSB of the anonymous object to the LSB of the
- bitfield.
-
- If the field is signed, we also do sign extension. */
-
-int
-unpack_value_bits_as_long (struct type *field_type, const gdb_byte *valaddr,
- int embedded_offset, int bitpos, int bitsize,
- const struct value *original_value,
- LONGEST *result)
-{
- gdb_assert (original_value != NULL);
-
- return unpack_value_bits_as_long_1 (field_type, valaddr, embedded_offset,
- bitpos, bitsize, original_value, result);
-
-}
-
-/* Unpack a field FIELDNO of the specified TYPE, from the object at
- VALADDR + EMBEDDED_OFFSET. VALADDR points to the contents of
- ORIGINAL_VALUE. See unpack_value_bits_as_long for more
- details. */
-
-static int
-unpack_value_field_as_long_1 (struct type *type, const gdb_byte *valaddr,
- int embedded_offset, int fieldno,
- const struct value *val, LONGEST *result)
-{
- int bitpos = TYPE_FIELD_BITPOS (type, fieldno);
- int bitsize = TYPE_FIELD_BITSIZE (type, fieldno);
- struct type *field_type = TYPE_FIELD_TYPE (type, fieldno);
-
- return unpack_value_bits_as_long_1 (field_type, valaddr, embedded_offset,
- bitpos, bitsize, val,
- result);
+ return val;
}

/* Unpack a field FIELDNO of the specified TYPE, from the object at
@@ -3231,51 +3193,95 @@ unpack_value_field_as_long (struct type *type, const gdb_byte *valaddr,
int embedded_offset, int fieldno,
const struct value *val, LONGEST *result)
{
+ int bitpos = TYPE_FIELD_BITPOS (type, fieldno);
+ int bitsize = TYPE_FIELD_BITSIZE (type, fieldno);
+ struct type *field_type = TYPE_FIELD_TYPE (type, fieldno);
+ int bit_offset;
+
gdb_assert (val != NULL);

- return unpack_value_field_as_long_1 (type, valaddr, embedded_offset,
- fieldno, val, result);
+ bit_offset = embedded_offset * TARGET_CHAR_BIT + bitpos;
+ if (value_bits_any_optimized_out (val, bit_offset, bitsize)
+ || !value_bits_available (val, bit_offset, bitsize))
+ return 0;
+
+ *result = unpack_bits_as_long (field_type, valaddr + embedded_offset,
+ bitpos, bitsize);
+ return 1;
}

/* Unpack a field FIELDNO of the specified TYPE, from the anonymous
- object at VALADDR. See unpack_value_bits_as_long for more details.
- This function differs from unpack_value_field_as_long in that it
- operates without a struct value object. */
+ object at VALADDR. See unpack_bits_as_long for more details. */

LONGEST
unpack_field_as_long (struct type *type, const gdb_byte *valaddr, int fieldno)
{
- LONGEST result;
+ int bitpos = TYPE_FIELD_BITPOS (type, fieldno);
+ int bitsize = TYPE_FIELD_BITSIZE (type, fieldno);
+ struct type *field_type = TYPE_FIELD_TYPE (type, fieldno);

- unpack_value_field_as_long_1 (type, valaddr, 0, fieldno, NULL, &result);
- return result;
+ return unpack_bits_as_long (field_type, valaddr, bitpos, bitsize);
+}
+
+/* Unpack a bitfield of BITSIZE bits found at BITPOS in the object at
+ VALADDR + EMBEDDEDOFFSET that has the type of DEST_VAL and store
+ the contents in DEST_VAL, zero or sign extending if the type of
+ DEST_VAL is wider than BITSIZE. VALADDR points to the contents of
+ VAL. If the VAL's contents required to extract the bitfield from
+ are unavailable/optimized out, DEST_VAL is correspondingly
+ marked unavailable/optimized out. */
+
+static void
+unpack_value_bitfield (struct value *dest_val,
+ int bitpos, int bitsize,
+ const gdb_byte *valaddr, int embedded_offset,
+ const struct value *val)
+{
+ enum bfd_endian byte_order;
+ int src_bit_offset;
+ int dst_bit_offset;
+ LONGEST num;
+ struct type *field_type = value_type (dest_val);
+
+ /* First, unpack and sign extend the bitfield as if it was wholly
+ available. Invalid/unavailable bits are read as zero, but that's
+ OK, as they'll end up marked below. */
+ byte_order = gdbarch_byte_order (get_type_arch (field_type));
+ num = unpack_bits_as_long (field_type, valaddr + embedded_offset,
+ bitpos, bitsize);
+ store_signed_integer (value_contents_raw (dest_val),
+ TYPE_LENGTH (field_type), byte_order, num);
+
+ /* Now copy the optimized out / unavailability ranges to the right
+ bits. */
+ src_bit_offset = embedded_offset * TARGET_CHAR_BIT + bitpos;
+ if (byte_order == BFD_ENDIAN_BIG)
+ dst_bit_offset = TYPE_LENGTH (field_type) * TARGET_CHAR_BIT - bitsize;
+ else
+ dst_bit_offset = 0;
+ value_ranges_copy_adjusted (dest_val, dst_bit_offset,
+ val, src_bit_offset, bitsize);
}

/* Return a new value with type TYPE, which is FIELDNO field of the
object at VALADDR + EMBEDDEDOFFSET. VALADDR points to the contents
of VAL. If the VAL's contents required to extract the bitfield
- from are unavailable, the new value is correspondingly marked as
- unavailable. */
+ from are unavailable/optimized out, the new value is
+ correspondingly marked unavailable/optimized out. */

struct value *
value_field_bitfield (struct type *type, int fieldno,
const gdb_byte *valaddr,
int embedded_offset, const struct value *val)
{
- LONGEST l;
+ int bitpos = TYPE_FIELD_BITPOS (type, fieldno);
+ int bitsize = TYPE_FIELD_BITSIZE (type, fieldno);
+ struct value *res_val = allocate_value (TYPE_FIELD_TYPE (type, fieldno));

- if (!unpack_value_field_as_long (type, valaddr, embedded_offset, fieldno,
- val, &l))
- {
- struct type *field_type = TYPE_FIELD_TYPE (type, fieldno);
- struct value *retval = allocate_value (field_type);
- mark_value_bytes_unavailable (retval, 0, TYPE_LENGTH (field_type));
- return retval;
- }
- else
- {
- return value_from_longest (TYPE_FIELD_TYPE (type, fieldno), l);
- }
+ unpack_value_bitfield (res_val, bitpos, bitsize,
+ valaddr, embedded_offset, val);
+
+ return res_val;
}

/* Modify the value of a bitfield. ADDR points to a block of memory in
@@ -3757,30 +3763,15 @@ value_fetch_lazy (struct value *val)
word, but we have no way to record that just specific bits of a
value have been fetched. */
struct type *type = check_typedef (value_type (val));
- enum bfd_endian byte_order = gdbarch_byte_order (get_type_arch (type));
struct value *parent = value_parent (val);
- LONGEST offset = value_offset (val);
- LONGEST num;

if (value_lazy (parent))
value_fetch_lazy (parent);

- if (value_bits_any_optimized_out (parent,
- TARGET_CHAR_BIT * offset + value_bitpos (val),
- value_bitsize (val)))
- mark_value_bytes_optimized_out (val, value_embedded_offset (val),
- TYPE_LENGTH (type));
- else if (!unpack_value_bits_as_long (value_type (val),
- value_contents_for_printing (parent),
- offset,
- value_bitpos (val),
- value_bitsize (val), parent, &num))
- mark_value_bytes_unavailable (val,
- value_embedded_offset (val),
- TYPE_LENGTH (type));
- else
- store_signed_integer (value_contents_raw (val), TYPE_LENGTH (type),
- byte_order, num);
+ unpack_value_bitfield (val,
+ value_bitpos (val), value_bitsize (val),
+ value_contents_for_printing (parent),
+ value_offset (val), parent);
}
else if (VALUE_LVAL (val) == lval_memory)
{
diff --git a/gdb/value.h b/gdb/value.h
index 5d4949c..4cdbf21 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -606,13 +606,6 @@ extern DOUBLEST unpack_double (struct type *type, const gdb_byte *valaddr,
int *invp);
extern CORE_ADDR unpack_pointer (struct type *type, const gdb_byte *valaddr);

-extern int unpack_value_bits_as_long (struct type *field_type,
- const gdb_byte *valaddr,
- int embedded_offset, int bitpos,
- int bitsize,
- const struct value *original_value,
- LONGEST *result);
-
extern LONGEST unpack_field_as_long (struct type *type,
const gdb_byte *valaddr,
int fieldno);
--
1.9.3