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[PR gdb/19893] Fix handling of synthetic C++ references

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https://sourceware.org/bugzilla/show_bug.cgi?id=19893

I've traced the main source of the problem to pieced_value_funcs.coerce_ref not being
implemented. Since gdb always assumes references are implemented as pointers, this
causes it to think that it's dealing with a NULL pointer, thus breaking any operations
involving synthetic references.

What I did here was implementing pieced_value_funcs.coerce_ref using some of the synthetic
pointer handling code from indirect_pieced_value, as Pedro suggested. I also made a few
adjustments to the reference printing code so that it correctly shows either the address
of the referenced value or (if it's non-addressable) the "<synthetic pointer>" string.

I also wrote some unit tests based on Dwarf::assemble; these took a while to make
because in most cases I needed a synthetic reference to a physical variable. Additionally,
I started working on a unit test for classes that have a vtable, but ran into a few issues
so that'll probably go in a future patch. One thing that should definitely be fixed is that
proc function_range (called for MACRO_AT_func) will always try to compile/link using gcc
with the default options instead of g++, thus breaking C++ compilations that require e.g. libstdc++.

gdb/ChangeLog:

	* dwarf2loc.c (coerce_pieced_ref, indirect_synthetic_pointer,
	fetch_const_value_from_synthetic_pointer): New functions.
	(indirect_pieced_value): Move lower half to indirect_synthetic_pointer.
	(pieced_value_funcs): Implement coerce_ref.
	* valops.c (value_addr): Call coerce_ref for synthetic references.
	* valprint.c (valprint_check_validity): Return true for synthetic
	references.  Also, don't show "<synthetic pointer>" if they reference
	addressable values.
	(generic_val_print_ref): Handle synthetic references.  Also move some
	code to print_ref_address.
	(print_ref_address, get_value_addr_contents): New functions.

gdb/testsuite/ChangeLog:

	* gdb.dwarf2/implref.exp: Rename to...
	* gdb.dwarf2/implref-const.exp: ...this.  Also add more test statements.
	* gdb.dwarf2/implref-array.c: New file.
	* gdb.dwarf2/implref-array.exp: Likewise.
	* gdb.dwarf2/implref-global.c: Likewise.
	* gdb.dwarf2/implref-global.exp: Likewise.
	* gdb.dwarf2/implref-struct.c: Likewise.
	* gdb.dwarf2/implref-struct.exp: Likewise.
This commit is contained in:
Martin Galvan
2016-05-31 15:54:01 -03:00
parent f7433f011e
commit 3326303bf5
12 changed files with 848 additions and 90 deletions
Download Patch File Download Diff File Expand all files Collapse all files

121
gdb/valprint.c
View File

@@ -335,8 +335,22 @@ valprint_check_validity (struct ui_file *stream,
if (value_bits_synthetic_pointer (val, TARGET_CHAR_BIT * embedded_offset,
TARGET_CHAR_BIT * TYPE_LENGTH (type)))
{
fputs_filtered (_("<synthetic pointer>"), stream);
return 0;
const int is_ref = TYPE_CODE (type) == TYPE_CODE_REF;
int ref_is_addressable = 0;
if (is_ref)
{
const struct value *deref_val = coerce_ref_if_computed (val);
if (deref_val != NULL)
ref_is_addressable = value_lval_const (deref_val) == lval_memory;
}
if (!is_ref || !ref_is_addressable)
fputs_filtered (_("<synthetic pointer>"), stream);
/* C++ references should be valid even if they're synthetic. */
return is_ref;
}
if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
@@ -484,6 +498,42 @@ generic_val_print_memberptr (struct type *type, const gdb_byte *valaddr,
original_value, options, 0, stream);
}
/* Print '@' followed by the address contained in ADDRESS_BUFFER. */
static void
print_ref_address (struct type *type, const gdb_byte *address_buffer,
int embedded_offset, struct ui_file *stream)
{
struct gdbarch *gdbarch = get_type_arch (type);
if (address_buffer != NULL)
{
CORE_ADDR address
= extract_typed_address (address_buffer + embedded_offset, type);
fprintf_filtered (stream, "@");
fputs_filtered (paddress (gdbarch, address), stream);
}
/* Else: we have a non-addressable value, such as a DW_AT_const_value. */
}
/* If VAL is addressable, return the value contents buffer of a value that
represents a pointer to VAL. Otherwise return NULL. */
static const gdb_byte *
get_value_addr_contents (struct value *deref_val)
{
gdb_assert (deref_val != NULL);
if (value_lval_const (deref_val) == lval_memory)
return value_contents_for_printing_const (value_addr (deref_val));
else
{
/* We have a non-addressable value, such as a DW_AT_const_value. */
return NULL;
}
}
/* generic_val_print helper for TYPE_CODE_REF. */
static void
@@ -492,41 +542,58 @@ generic_val_print_ref (struct type *type, const gdb_byte *valaddr,
const struct value *original_value,
const struct value_print_options *options)
{
struct gdbarch *gdbarch = get_type_arch (type);
struct type *elttype = check_typedef (TYPE_TARGET_TYPE (type));
struct value *deref_val = NULL;
const int value_is_synthetic
= value_bits_synthetic_pointer (original_value,
TARGET_CHAR_BIT * embedded_offset,
TARGET_CHAR_BIT * TYPE_LENGTH (type));
const int must_coerce_ref = ((options->addressprint && value_is_synthetic)
|| options->deref_ref);
const int type_is_defined = TYPE_CODE (elttype) != TYPE_CODE_UNDEF;
if (must_coerce_ref && type_is_defined)
{
deref_val = coerce_ref_if_computed (original_value);
if (deref_val != NULL)
{
/* More complicated computed references are not supported. */
gdb_assert (embedded_offset == 0);
}
else
deref_val = value_at (TYPE_TARGET_TYPE (type),
unpack_pointer (type, valaddr + embedded_offset));
}
/* Else, original_value isn't a synthetic reference or we don't have to print
the reference's contents.
Notice that for references to TYPE_CODE_STRUCT, 'set print object on' will
cause original_value to be a not_lval instead of an lval_computed,
which will make value_bits_synthetic_pointer return false.
This happens because if options->objectprint is true, c_value_print will
overwrite original_value's contents with the result of coercing
the reference through value_addr, and then set its type back to
TYPE_CODE_REF. In that case we don't have to coerce the reference again;
we can simply treat it as non-synthetic and move on. */
if (options->addressprint)
{
CORE_ADDR addr
= extract_typed_address (valaddr + embedded_offset, type);
const gdb_byte *address = (value_is_synthetic && type_is_defined
? get_value_addr_contents (deref_val)
: valaddr);
print_ref_address (type, address, embedded_offset, stream);
fprintf_filtered (stream, "@");
fputs_filtered (paddress (gdbarch, addr), stream);
if (options->deref_ref)
fputs_filtered (": ", stream);
}
/* De-reference the reference. */
if (options->deref_ref)
{
if (TYPE_CODE (elttype) != TYPE_CODE_UNDEF)
{
struct value *deref_val;
deref_val = coerce_ref_if_computed (original_value);
if (deref_val != NULL)
{
/* More complicated computed references are not supported. */
gdb_assert (embedded_offset == 0);
}
else
deref_val = value_at (TYPE_TARGET_TYPE (type),
unpack_pointer (type,
(valaddr
+ embedded_offset)));
common_val_print (deref_val, stream, recurse, options,
current_language);
}
if (type_is_defined)
common_val_print (deref_val, stream, recurse, options,
current_language);
else
fputs_filtered ("???", stream);
}