The gdb.base/whatis-ptype-typedefs.exp testcase has several tests that
fail on 32-bit architectures. E.g., on 'x86-64 -m32', I see:
...
FAIL: gdb.base/whatis-ptype-typedefs.exp: lang=c: cast: whatis (float_typedef) v_uchar_array_t_struct_typedef (invalid)
FAIL: gdb.base/whatis-ptype-typedefs.exp: lang=c: cast: ptype (float_typedef) v_uchar_array_t_struct_typedef (invalid)
...
gdb.log:
(gdb) whatis (float_typedef) v_uchar_array_t_struct_typedef
type = float_typedef
(gdb) FAIL: gdb.base/whatis-ptype-typedefs.exp: lang=c: cast: whatis (float_typedef) v_uchar_array_t_struct_typedef (invalid)
As Simon explained [1], the issue boils down to the fact that on
64-bit, this is an invalid cast:
(gdb) p (float_typedef) v_uchar_array_t_struct_typedef
Invalid cast.
while on 32 bits it is valid:
(gdb) p (float_typedef) v_uchar_array_t_struct_typedef
$1 = 1.16251721e-41
The expression basically tries to cast an array (which decays to a
pointer) to a float. The cast works on 32 bits because a float and a
pointer are of the same size, and value_cast works in that case:
~~~
More general than a C cast: accepts any two types of the same length,
and if ARG2 is an lvalue it can be cast into anything at all. */
~~~
On 64 bits, they are not the same size, so it ends throwing the
"Invalid cast" error.
The testcase is expecting the invalid cast behavior, thus the FAILs.
A point of these tests was to cover as many code paths in value_cast
as possible, as a sort of documentation of the current behavior:
# The main idea here is testing all the different paths in the
# value casting code in GDB (value_cast), making sure typedefs are
# preserved.
...
# We try all combinations, even those that don't parse, or are
# invalid, to catch the case of a regression making them
# inadvertently valid. For example, these convertions are
# invalid:
...
In that spirit, this commit makes the testcase adjust itself depending
on size of floats and pointers, and also test floats of different
sizes.
Passes cleanly on x86-64 GNU/Linux both -m64/-m32.
[1] - https://sourceware.org/ml/gdb-patches/2017-11/msg00382.html
gdb/ChangeLog:
2017-11-20 Pedro Alves <palves@redhat.com>
* gdb.base/whatis-ptype-typedefs.c (double_typedef)
(long_double_typedef): New typedefs.
Use DEF on double and long double.
* gdb.base/whatis-ptype-typedefs.exp: Add double and long double
cases.
(run_tests): New 'float_ptr_same_size', 'double_ptr_same_size',
and 'long_double_ptr_same_size' locals. Use them to decide
whether cast from array/function to float is valid/invalid.
(Ref: https://sourceware.org/ml/gdb/2017-06/msg00020.html)
Assuming int_t is a typedef to int:
typedef int int_t;
gdb currently loses this expression's typedef:
(gdb) p (int_t) 0
$1 = 0
(gdb) whatis $1
type = int
or:
(gdb) whatis (int_t) 0
type = int
or, to get "whatis" out of the way:
(gdb) maint print type (int_t) 0
...
name 'int'
code 0x8 (TYPE_CODE_INT)
...
This prevents a type printer for "int_t" kicking in, with e.g.:
(gdb) p (int_t) 0
From the manual, we can see that that "whatis (int_t) 0" command
invocation should have printed "type = int_t":
If @var{arg} is a variable or an expression, @code{whatis} prints its
literal type as it is used in the source code. If the type was
defined using a @code{typedef}, @code{whatis} will @emph{not} print
the data type underlying the @code{typedef}.
(...)
If @var{arg} is a type name that was defined using @code{typedef},
@code{whatis} @dfn{unrolls} only one level of that @code{typedef}.
That one-level stripping is currently done here, in
gdb/eval.c:evaluate_subexp_standard, handling OP_TYPE:
...
else if (noside == EVAL_AVOID_SIDE_EFFECTS)
{
struct type *type = exp->elts[pc + 1].type;
/* If this is a typedef, then find its immediate target. We
use check_typedef to resolve stubs, but we ignore its
result because we do not want to dig past all
typedefs. */
check_typedef (type);
if (TYPE_CODE (type) == TYPE_CODE_TYPEDEF)
type = TYPE_TARGET_TYPE (type);
return allocate_value (type);
}
However, this stripping is reachable in both:
#1 - (gdb) whatis (int_t)0 # ARG is an expression with a cast to
# typedef type.
#2 - (gdb) whatis int_t # ARG is a type name.
while only case #2 should strip the typedef. Removing that code from
evaluate_subexp_standard is part of the fix. Instead, we make the
"whatis" command implementation itself strip one level of typedefs
when the command argument is a type name.
We then run into another problem, also fixed by this commit:
value_cast always drops any typedefs of the destination type.
With all that fixed, "whatis (int_t) 0" now works as expected:
(gdb) whatis int_t
type = int
(gdb) whatis (int_t)0
type = int_t
value_cast has many different exit/convertion paths, for handling many
different kinds of casts/conversions, and most of them had to be
tweaked to construct the value of the right "to" type. The new tests
try to exercise most of it, by trying castin of many different
combinations of types. With:
$ make check TESTS="*/whatis-ptype*.exp */gnu_vector.exp */dfp-test.exp"
... due to combinatorial explosion, the testsuite results for the
tests above alone grow like:
- # of expected passes 246
+ # of expected passes 3811
You'll note that the tests exposed one GCC buglet, filed here:
Missing DW_AT_type in DW_TAG_typedef of "typedef of typedef of void"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81267
gdb/ChangeLog:
2017-08-21 Pedro Alves <palves@redhat.com>
* eval.c (evaluate_subexp_standard) <OP_TYPE>: Don't dig past
typedefs.
* typeprint.c (whatis_exp): If handling "whatis", and expression
is OP_TYPE, strip one typedef level. Otherwise don't strip
typedefs here.
* valops.c (value_cast): Save "to" type before resolving
stubs/typedefs. Use that type as resulting value's type.
gdb/testsuite/ChangeLog:
2017-08-21 Pedro Alves <palves@redhat.com>
* gdb.base/dfp-test.c
(d32_t, d64_t, d128_t, d32_t2, d64_t2, d128_t2, v_d32_t, v_d64_t)
(v_d128_t, v_d32_t2, v_d64_t2, v_d128_t2): New.
* gdb.base/dfp-test.exp: Add whatis/ptype/cast tests.
* gdb.base/gnu_vector.exp: Add whatis/ptype/cast tests.
* gdb.base/whatis-ptype-typedefs.c: New.
* gdb.base/whatis-ptype-typedefs.exp: New.
* gdb.python/py-prettyprint.c (int_type, int_type2): New typedefs.
(an_int, an_int_type, an_int_type2): New globals.
* gdb.python/py-prettyprint.exp (run_lang_tests): Add tests
involving typedefs and cast expressions.
* gdb.python/py-prettyprint.py (class pp_int_typedef): New.
(lookup_typedefs_function): New.
(typedefs_pretty_printers_dict): New.
(top level): Register lookup_typedefs_function in
gdb.pretty_printers.
Pedro Alves