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binutils-gdb/gdb/compile/compile-c-types.c
Pedro Alves 46a4882b3c Stop assuming no-debug-info variables have type int 
An earlier commit made GDB no longer assume no-debug-info functions
return int.  This commit gives the same treatment to variables.

Currently, you can end misled by GDB over output like this:

  (gdb) p var
  $1 = -1
  (gdb) p /x var
  $2 = 0xffffffff

until you realize that GDB is assuming that the variable is an "int",
because:

  (gdb) ptype var
  type = <data variable, no debug info>

You may try to fix it by casting, but that doesn't really help:

  (gdb) p /x (unsigned long long) var
  $3 = 0xffffffffffffffff            # incorrect
         ^^

That's incorrect output, because the variable was defined like this:

  uint64_t var = 0x7fffffffffffffff;
                   ^^

What happened is that with the cast, GDB did an int -> 'unsigned long
long' conversion instead of reinterpreting the variable as the cast-to
type.  To get at the variable properly you have to reinterpret the
variable's address manually instead, with either:

  (gdb) p /x *(unsigned long long *) &var
  $4 = 0x7fffffffffffffff
  (gdb) p /x {unsigned long long} &var
  $5 = 0x7fffffffffffffff

After this commit GDB does it for you.  This is what you'll get
instead:

  (gdb) p var
  'var' has unknown type; cast it to its declared type
  (gdb) p /x (unsigned long long) var
  $1 = 0x7fffffffffffffff

As in the functions patch, the "compile" machinery doesn't currently
have the cast-to type handy, so it continues assuming no-debug
variables have int type, though now at least it warns.

The change to gdb.cp/m-static.exp deserves an explanation:

 - gdb_test "print 'gnu_obj_1::method()::sintvar'" "\\$\[0-9\]+ = 4" \
 + gdb_test "print (int) 'gnu_obj_1::method()::sintvar'" "\\$\[0-9\]+ = 4" \

That's printing the "sintvar" function local static of the
"gnu_obj_1::method()" method.

The problem with that test is that that "'S::method()::static_var'"
syntax doesn't really work in C++ as you'd expect.  The way to make it
work correctly currently is to quote the method part, not the whole
expression, like:

  (gdb) print 'gnu_obj_1::method()'::sintvar

If you wrap the whole expression in quotes, like in m-static.exp, what
really happens is that the parser considers the whole string as a
symbol name, but there's no debug symbol with that name.  However,
local statics have linkage and are given a mangled name that demangles
to the same string as the full expression, so that's what GDB prints.
After this commit, and without the cast, the print in m-static.exp
would error out saying that the variable has unknown type:

  (gdb) p 'gnu_obj_1::method()::sintvar'
  'gnu_obj_1::method()::sintvar' has unknown type; cast it to its declared type

TBC, if currently (even before this series) you try to print any
function local static variable of type other than int, you'll get
bogus results.  You can see that with m-static.cc as is, even.
Printing the "svar" local, which is a boolean (1 byte) still prints as
"int" (4 bytes):

  (gdb) p 'gnu_obj_1::method()::svar'
  $1 = 1
  (gdb) ptype 'gnu_obj_1::method()::svar'
  type = <data variable, no debug info>

This probably prints some random bogus value on big endian machines.

If 'svar' was of some aggregate type (etc.) we'd still print it as
int, so the problem would have been more obvious...  After this
commit, you'll get instead:

  (gdb) p 'gnu_obj_1::method()::svar'
  'gnu_obj_1::method()::svar' has unknown type; cast it to its declared type

... so at least GDB is no longer misleading.  Making GDB find the real
local static debug symbol is the subject of the following patches.  In
the end, it'll all "Just Work".

gdb/ChangeLog:
2017-09-04  Pedro Alves  <palves@redhat.com>

	* ax-gdb.c: Include "typeprint.h".
	(gen_expr_for_cast): New function.
	(gen_expr) <OP_CAST, OP_CAST_TYPE>: Use it.
	<OP_VAR_VALUE, OP_MSYM_VAR_VALUE>: Error out if the variable's
	type is unknown.
	* dwarf2read.c (new_symbol_full): Fallback to int instead of
	nodebug_data_symbol.
	* eval.c: Include "typeprint.h".
	(evaluate_subexp_standard) <OP_VAR_VALUE, OP_VAR_MSYM_VALUE>:
	Error out if symbol has unknown type.
	<UNOP_CAST, UNOP_CAST_TYPE>: Common bits factored out to
	evaluate_subexp_for_cast.
	(evaluate_subexp_for_address, evaluate_subexp_for_sizeof): Handle
	OP_VAR_MSYM_VALUE.
	(evaluate_subexp_for_cast): New function.
	* gdbtypes.c (init_nodebug_var_type): New function.
	(objfile_type): Use it to initialize types of variables with no
	debug info.
	* typeprint.c (error_unknown_type): New.
	* typeprint.h (error_unknown_type): New declaration.
	* compile/compile-c-types.c (convert_type_basic): Handle
	TYPE_CODE_ERROR; warn and fallback to int for variables with
	unknown type.

gdb/testsuite/ChangeLog:
2017-09-04  Pedro Alves  <palves@redhat.com>

	* gdb.asm/asm-source.exp: Add casts to int.
	* gdb.base/nodebug.c (dataglobal8, dataglobal32_1, dataglobal32_2)
	(dataglobal64_1, dataglobal64_2): New globals.
	* gdb.base/nodebug.exp: Test different expressions involving the
	new globals, with print, whatis and ptype.  Add casts to int.
	* gdb.base/solib-display.exp: Add casts to int.
	* gdb.compile/compile-ifunc.exp: Expect warning.  Add cast to int.
	* gdb.cp/m-static.exp: Add cast to int.
	* gdb.dwarf2/dw2-skip-prologue.exp: Add cast to int.
	* gdb.threads/tls-nodebug.exp: Check that gdb errors out printing
	tls variable with no debug info without a cast.  Test with a cast
	to int too.
	* gdb.trace/entry-values.exp: Add casts.
2017-09-04 20:21:15 +01:00

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/* Convert types from GDB to GCC
Copyright (C) 2014-2017 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
#include "gdbtypes.h"
#include "compile-internal.h"
#include "objfiles.h"
/* An object that maps a gdb type to a gcc type. */
struct type_map_instance
{
/* The gdb type. */
struct type *type;
/* The corresponding gcc type handle. */
gcc_type gcc_type_handle;
};
/* Hash a type_map_instance. */
static hashval_t
hash_type_map_instance (const void *p)
{
const struct type_map_instance *inst = (const struct type_map_instance *) p;
return htab_hash_pointer (inst->type);
}
/* Check two type_map_instance objects for equality. */
static int
eq_type_map_instance (const void *a, const void *b)
{
const struct type_map_instance *insta = (const struct type_map_instance *) a;
const struct type_map_instance *instb = (const struct type_map_instance *) b;
return insta->type == instb->type;
}
/* Insert an entry into the type map associated with CONTEXT that maps
from the gdb type TYPE to the gcc type GCC_TYPE. It is ok for a
given type to be inserted more than once, provided that the exact
same association is made each time. This simplifies how type
caching works elsewhere in this file -- see how struct type caching
is handled. */
static void
insert_type (struct compile_c_instance *context, struct type *type,
gcc_type gcc_type)
{
struct type_map_instance inst, *add;
void **slot;
inst.type = type;
inst.gcc_type_handle = gcc_type;
slot = htab_find_slot (context->type_map, &inst, INSERT);
add = (struct type_map_instance *) *slot;
/* The type might have already been inserted in order to handle
recursive types. */
if (add != NULL && add->gcc_type_handle != gcc_type)
error (_("Unexpected type id from GCC, check you use recent enough GCC."));
if (add == NULL)
{
add = XNEW (struct type_map_instance);
*add = inst;
*slot = add;
}
}
/* Convert a pointer type to its gcc representation. */
static gcc_type
convert_pointer (struct compile_c_instance *context, struct type *type)
{
gcc_type target = convert_type (context, TYPE_TARGET_TYPE (type));
return C_CTX (context)->c_ops->build_pointer_type (C_CTX (context),
target);
}
/* Convert an array type to its gcc representation. */
static gcc_type
convert_array (struct compile_c_instance *context, struct type *type)
{
gcc_type element_type;
struct type *range = TYPE_INDEX_TYPE (type);
element_type = convert_type (context, TYPE_TARGET_TYPE (type));
if (TYPE_LOW_BOUND_KIND (range) != PROP_CONST)
return C_CTX (context)->c_ops->error (C_CTX (context),
_("array type with non-constant"
" lower bound is not supported"));
if (TYPE_LOW_BOUND (range) != 0)
return C_CTX (context)->c_ops->error (C_CTX (context),
_("cannot convert array type with "
"non-zero lower bound to C"));
if (TYPE_HIGH_BOUND_KIND (range) == PROP_LOCEXPR
|| TYPE_HIGH_BOUND_KIND (range) == PROP_LOCLIST)
{
gcc_type result;
if (TYPE_VECTOR (type))
return C_CTX (context)->c_ops->error (C_CTX (context),
_("variably-sized vector type"
" is not supported"));
std::string upper_bound
= c_get_range_decl_name (&TYPE_RANGE_DATA (range)->high);
result = C_CTX (context)->c_ops->build_vla_array_type (C_CTX (context),
element_type,
upper_bound.c_str ());
return result;
}
else
{
LONGEST low_bound, high_bound, count;
if (get_array_bounds (type, &low_bound, &high_bound) == 0)
count = -1;
else
{
gdb_assert (low_bound == 0); /* Ensured above. */
count = high_bound + 1;
}
if (TYPE_VECTOR (type))
return C_CTX (context)->c_ops->build_vector_type (C_CTX (context),
element_type,
count);
return C_CTX (context)->c_ops->build_array_type (C_CTX (context),
element_type, count);
}
}
/* Convert a struct or union type to its gcc representation. */
static gcc_type
convert_struct_or_union (struct compile_c_instance *context, struct type *type)
{
int i;
gcc_type result;
/* First we create the resulting type and enter it into our hash
table. This lets recursive types work. */
if (TYPE_CODE (type) == TYPE_CODE_STRUCT)
result = C_CTX (context)->c_ops->build_record_type (C_CTX (context));
else
{
gdb_assert (TYPE_CODE (type) == TYPE_CODE_UNION);
result = C_CTX (context)->c_ops->build_union_type (C_CTX (context));
}
insert_type (context, type, result);
for (i = 0; i < TYPE_NFIELDS (type); ++i)
{
gcc_type field_type;
unsigned long bitsize = TYPE_FIELD_BITSIZE (type, i);
field_type = convert_type (context, TYPE_FIELD_TYPE (type, i));
if (bitsize == 0)
bitsize = 8 * TYPE_LENGTH (TYPE_FIELD_TYPE (type, i));
C_CTX (context)->c_ops->build_add_field (C_CTX (context), result,
TYPE_FIELD_NAME (type, i),
field_type,
bitsize,
TYPE_FIELD_BITPOS (type, i));
}
C_CTX (context)->c_ops->finish_record_or_union (C_CTX (context), result,
TYPE_LENGTH (type));
return result;
}
/* Convert an enum type to its gcc representation. */
static gcc_type
convert_enum (struct compile_c_instance *context, struct type *type)
{
gcc_type int_type, result;
int i;
struct gcc_c_context *ctx = C_CTX (context);
int_type = ctx->c_ops->int_type (ctx,
TYPE_UNSIGNED (type),
TYPE_LENGTH (type));
result = ctx->c_ops->build_enum_type (ctx, int_type);
for (i = 0; i < TYPE_NFIELDS (type); ++i)
{
ctx->c_ops->build_add_enum_constant (ctx,
result,
TYPE_FIELD_NAME (type, i),
TYPE_FIELD_ENUMVAL (type, i));
}
ctx->c_ops->finish_enum_type (ctx, result);
return result;
}
/* Convert a function type to its gcc representation. */
static gcc_type
convert_func (struct compile_c_instance *context, struct type *type)
{
int i;
gcc_type result, return_type;
struct gcc_type_array array;
int is_varargs = TYPE_VARARGS (type) || !TYPE_PROTOTYPED (type);
struct type *target_type = TYPE_TARGET_TYPE (type);
/* Functions with no debug info have no return type. Ideally we'd
want to fallback to the type of the cast just before the
function, like GDB's built-in expression parser, but we don't
have access to that type here. For now, fallback to int, like
GDB's parser used to do. */
if (target_type == NULL)
{
if (TYPE_OBJFILE_OWNED (type))
target_type = objfile_type (TYPE_OWNER (type).objfile)->builtin_int;
else
target_type = builtin_type (TYPE_OWNER (type).gdbarch)->builtin_int;
warning (_("function has unknown return type; assuming int"));
}
/* This approach means we can't make self-referential function
types. Those are impossible in C, though. */
return_type = convert_type (context, target_type);
array.n_elements = TYPE_NFIELDS (type);
array.elements = XNEWVEC (gcc_type, TYPE_NFIELDS (type));
for (i = 0; i < TYPE_NFIELDS (type); ++i)
array.elements[i] = convert_type (context, TYPE_FIELD_TYPE (type, i));
result = C_CTX (context)->c_ops->build_function_type (C_CTX (context),
return_type,
&array, is_varargs);
xfree (array.elements);
return result;
}
/* Convert an integer type to its gcc representation. */
static gcc_type
convert_int (struct compile_c_instance *context, struct type *type)
{
return C_CTX (context)->c_ops->int_type (C_CTX (context),
TYPE_UNSIGNED (type),
TYPE_LENGTH (type));
}
/* Convert a floating-point type to its gcc representation. */
static gcc_type
convert_float (struct compile_c_instance *context, struct type *type)
{
return C_CTX (context)->c_ops->float_type (C_CTX (context),
TYPE_LENGTH (type));
}
/* Convert the 'void' type to its gcc representation. */
static gcc_type
convert_void (struct compile_c_instance *context, struct type *type)
{
return C_CTX (context)->c_ops->void_type (C_CTX (context));
}
/* Convert a boolean type to its gcc representation. */
static gcc_type
convert_bool (struct compile_c_instance *context, struct type *type)
{
return C_CTX (context)->c_ops->bool_type (C_CTX (context));
}
/* Convert a qualified type to its gcc representation. */
static gcc_type
convert_qualified (struct compile_c_instance *context, struct type *type)
{
struct type *unqual = make_unqualified_type (type);
gcc_type unqual_converted;
gcc_qualifiers_flags quals = 0;
unqual_converted = convert_type (context, unqual);
if (TYPE_CONST (type))
quals |= GCC_QUALIFIER_CONST;
if (TYPE_VOLATILE (type))
quals |= GCC_QUALIFIER_VOLATILE;
if (TYPE_RESTRICT (type))
quals |= GCC_QUALIFIER_RESTRICT;
return C_CTX (context)->c_ops->build_qualified_type (C_CTX (context),
unqual_converted,
quals);
}
/* Convert a complex type to its gcc representation. */
static gcc_type
convert_complex (struct compile_c_instance *context, struct type *type)
{
gcc_type base = convert_type (context, TYPE_TARGET_TYPE (type));
return C_CTX (context)->c_ops->build_complex_type (C_CTX (context), base);
}
/* A helper function which knows how to convert most types from their
gdb representation to the corresponding gcc form. This examines
the TYPE and dispatches to the appropriate conversion function. It
returns the gcc type. */
static gcc_type
convert_type_basic (struct compile_c_instance *context, struct type *type)
{
/* If we are converting a qualified type, first convert the
unqualified type and then apply the qualifiers. */
if ((TYPE_INSTANCE_FLAGS (type) & (TYPE_INSTANCE_FLAG_CONST
| TYPE_INSTANCE_FLAG_VOLATILE
| TYPE_INSTANCE_FLAG_RESTRICT)) != 0)
return convert_qualified (context, type);
switch (TYPE_CODE (type))
{
case TYPE_CODE_PTR:
return convert_pointer (context, type);
case TYPE_CODE_ARRAY:
return convert_array (context, type);
case TYPE_CODE_STRUCT:
case TYPE_CODE_UNION:
return convert_struct_or_union (context, type);
case TYPE_CODE_ENUM:
return convert_enum (context, type);
case TYPE_CODE_FUNC:
return convert_func (context, type);
case TYPE_CODE_INT:
return convert_int (context, type);
case TYPE_CODE_FLT:
return convert_float (context, type);
case TYPE_CODE_VOID:
return convert_void (context, type);
case TYPE_CODE_BOOL:
return convert_bool (context, type);
case TYPE_CODE_COMPLEX:
return convert_complex (context, type);
case TYPE_CODE_ERROR:
{
/* Ideally, if we get here due to a cast expression, we'd use
the cast-to type as the variable's type, like GDB's
built-in parser does. For now, assume "int" like GDB's
built-in parser used to do, but at least warn. */
struct type *fallback;
if (TYPE_OBJFILE_OWNED (type))
fallback = objfile_type (TYPE_OWNER (type).objfile)->builtin_int;
else
fallback = builtin_type (TYPE_OWNER (type).gdbarch)->builtin_int;
warning (_("variable has unknown type; assuming int"));
return convert_int (context, fallback);
}
}
return C_CTX (context)->c_ops->error (C_CTX (context),
_("cannot convert gdb type "
"to gcc type"));
}
/* See compile-internal.h. */
gcc_type
convert_type (struct compile_c_instance *context, struct type *type)
{
struct type_map_instance inst, *found;
gcc_type result;
/* We don't ever have to deal with typedefs in this code, because
those are only needed as symbols by the C compiler. */
type = check_typedef (type);
inst.type = type;
found = (struct type_map_instance *) htab_find (context->type_map, &inst);
if (found != NULL)
return found->gcc_type_handle;
result = convert_type_basic (context, type);
insert_type (context, type, result);
return result;
}
/* Delete the compiler instance C. */
static void
delete_instance (struct compile_instance *c)
{
struct compile_c_instance *context = (struct compile_c_instance *) c;
context->base.fe->ops->destroy (context->base.fe);
htab_delete (context->type_map);
if (context->symbol_err_map != NULL)
htab_delete (context->symbol_err_map);
xfree (context);
}
/* See compile-internal.h. */
struct compile_instance *
new_compile_instance (struct gcc_c_context *fe)
{
struct compile_c_instance *result = XCNEW (struct compile_c_instance);
result->base.fe = &fe->base;
result->base.destroy = delete_instance;
result->base.gcc_target_options = ("-std=gnu11"
/* Otherwise the .o file may need
"_Unwind_Resume" and
"__gcc_personality_v0". */
" -fno-exceptions");
result->type_map = htab_create_alloc (10, hash_type_map_instance,
eq_type_map_instance,
xfree, xcalloc, xfree);
fe->c_ops->set_callbacks (fe, gcc_convert_symbol,
gcc_symbol_address, result);
return &result->base;
}
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