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binutils-gdb/gdb/f-typeprint.c
Pedro Alves 7022349d5c Stop assuming no-debug-info functions return int 
The fact that GDB defaults to assuming that functions return int, when
it has no debug info for the function has been a recurring source of
user confusion.  Recently this came up on the errno pretty printer
discussions.  Shortly after, it came up again on IRC, with someone
wondering why does getenv() in GDB return a negative int:

  (gdb) p getenv("PATH")
  $1 = -6185

This question (with s/getenv/random-other-C-runtime-function) is a FAQ
on IRC.

The reason for the above is:

 (gdb) p getenv
 $2 = {<text variable, no debug info>} 0x7ffff7751d80 <getenv>
 (gdb) ptype getenv
 type = int ()

... which means that GDB truncated the 64-bit pointer that is actually
returned from getent to 32-bit, and then sign-extended it:

 (gdb) p /x -6185
 $6 = 0xffffe7d7

The workaround is to cast the function to the right type, like:

 (gdb) p ((char *(*) (const char *)) getenv) ("PATH")
 $3 = 0x7fffffffe7d7 "/usr/local/bin:/"...

IMO, we should do better than this.

I see the "assume-int" issue the same way I see printing bogus values
for optimized-out variables instead of "<optimized out>" -- I'd much
rather that the debugger tells me "I don't know" and tells me how to
fix it than showing me bogus misleading results, making me go around
tilting at windmills.

If GDB prints a signed integer when you're expecting a pointer or
aggregate, you at least have some sense that something is off, but
consider the case of the function actually returning a 64-bit integer.
For example, compile this without debug info:

 unsigned long long
 function ()
 {
   return 0x7fffffffffffffff;
 }

Currently, with pristine GDB, you get:

 (gdb) p function ()
 $1 = -1                      # incorrect
 (gdb) p /x function ()
 $2 = 0xffffffff              # incorrect

maybe after spending a few hours debugging you suspect something is
wrong with that -1, and do:

 (gdb) ptype function
 type = int ()

and maybe, just maybe, you realize that the function actually returns
unsigned long long.  And you try to fix it with:

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

... which still produces the wrong result, because GDB simply applied
int to unsigned long long conversion.  Meaning, it sign-extended the
integer that it extracted from the return of the function, to 64-bits.

and then maybe, after asking around on IRC, you realize you have to
cast the function to a pointer of the right type, and call that.  It
won't be easy, but after a few missteps, you'll get to it:

.....  (gdb) p /x ((unsigned long long(*) ()) function) ()
 $666 = 0x7fffffffffffffff             # finally! :-)


So to improve on the user experience, this patch does the following
(interrelated) things:

 - makes no-debug-info functions no longer default to "int" as return
   type.  Instead, they're left with NULL/"<unknown return type>"
   return type.

    (gdb) ptype getenv
    type = <unknown return type> ()

 - makes calling a function with unknown return type an error.

    (gdb) p getenv ("PATH")
    'getenv' has unknown return type; cast the call to its declared return type

 - and then to make it easier to call the function, makes it possible
   to _only_ cast the return of the function to the right type,
   instead of having to cast the function to a function pointer:

    (gdb) p (char *) getenv ("PATH")                      # now Just Works
    $3 = 0x7fffffffe7d7 "/usr/local/bin:/"...

    (gdb) p ((char *(*) (const char *)) getenv) ("PATH")  # continues working
    $4 = 0x7fffffffe7d7 "/usr/local/bin:/"...

   I.e., it makes GDB default the function's return type to the type
   of the cast, and the function's parameters to the type of the
   arguments passed down.

After this patch, here's what you'll get for the "unsigned long long"
example above:

 (gdb) p function ()
 'function' has unknown return type; cast the call to its declared return type
 (gdb) p /x (unsigned long long) function ()
 $4 = 0x7fffffffffffffff     # correct!

Note that while with "print" GDB shows the name of the function that
has the problem:

  (gdb) p getenv ("PATH")
  'getenv' has unknown return type; cast the call to its declared return type

which can by handy in more complicated expressions, "ptype" does not:

  (gdb) ptype getenv ("PATH")
  function has unknown return type; cast the call to its declared return type

This will be fixed in the next patch.

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

	* ada-lang.c (ada_evaluate_subexp) <TYPE_CODE_FUNC>: Don't handle
	TYPE_GNU_IFUNC specially here.  Throw error if return type is
	unknown.
	* ada-typeprint.c (print_func_type): Handle functions with unknown
	return type.
	* c-typeprint.c (c_type_print_base): Handle functions and methods
	with unknown return type.
	* compile/compile-c-symbols.c (convert_symbol_bmsym)
	<mst_text_gnu_ifunc>: Use nodebug_text_gnu_ifunc_symbol.
	* compile/compile-c-types.c: Include "objfiles.h".
	(convert_func): For functions with unknown return type, warn and
	default to int.
	* compile/compile-object-run.c (compile_object_run): Adjust call
	to call_function_by_hand_dummy.
	* elfread.c (elf_gnu_ifunc_resolve_addr): Adjust call to
	call_function_by_hand.
	* eval.c (evaluate_subexp_standard): Adjust calls to
	call_function_by_hand.  Handle functions and methods with unknown
	return type.  Pass expect_type to call_function_by_hand.
	* f-typeprint.c (f_type_print_base): Handle functions with unknown
	return type.
	* gcore.c (call_target_sbrk): Adjust call to
	call_function_by_hand.
	* gdbtypes.c (objfile_type): Leave nodebug text symbol with NULL
	return type instead of int.  Make nodebug_text_gnu_ifunc_symbol be
	an integer address type instead of nodebug.
	* guile/scm-value.c (gdbscm_value_call): Adjust call to
	call_function_by_hand.
	* infcall.c (error_call_unknown_return_type): New function.
	(call_function_by_hand): New "default_return_type" parameter.
	Pass it down.
	(call_function_by_hand_dummy): New "default_return_type"
	parameter.  Use it instead of defaulting to int.  If there's no
	default and the return type is unknown, throw an error.  If
	there's a default return type, and the called function has no
	debug info, then assume the function is prototyped.
	* infcall.h (call_function_by_hand, call_function_by_hand_dummy):
	New "default_return_type" parameter.
	(error_call_unknown_return_type): New declaration.
	* linux-fork.c (call_lseek): Cast return type of lseek.
	(inferior_call_waitpid, checkpoint_command): Adjust calls to
	call_function_by_hand.
	* linux-tdep.c (linux_infcall_mmap, linux_infcall_munmap): Adjust
	calls to call_function_by_hand.
	* m2-typeprint.c (m2_procedure): Handle functions with unknown
	return type.
	* objc-lang.c (lookup_objc_class, lookup_child_selector)
	(value_nsstring, print_object_command): Adjust calls to
	call_function_by_hand.
	* p-typeprint.c (pascal_type_print_varspec_prefix): Handle
	functions with unknown return type.
	(pascal_type_print_func_varspec_suffix): New function.
	(pascal_type_print_varspec_suffix) <TYPE_CODE_FUNC,
	TYPE_CODE_METHOD>: Use it.
	* python/py-value.c (valpy_call): Adjust call to
	call_function_by_hand.
	* rust-lang.c (rust_evaluate_funcall): Adjust call to
	call_function_by_hand.
	* valarith.c (value_x_binop, value_x_unop): Adjust calls to
	call_function_by_hand.
	* valops.c (value_allocate_space_in_inferior): Adjust call to
	call_function_by_hand.
	* typeprint.c (type_print_unknown_return_type): New function.
	* typeprint.h (type_print_unknown_return_type): New declaration.

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

	* gdb.base/break-main-file-remove-fail.exp (test_remove_bp): Cast
	return type of munmap in infcall.
	* gdb.base/break-probes.exp: Cast return type of foo in infcall.
	* gdb.base/checkpoint.exp: Simplify using for loop.  Cast return
	type of ftell in infcall.
	* gdb.base/dprintf-detach.exp (dprintf_detach_test): Cast return
	type of getpid in infcall.
	* gdb.base/infcall-exec.exp: Cast return type of execlp in
	infcall.
	* gdb.base/info-os.exp: Cast return type of getpid in infcall.
	Bail on failure to extract the pid.
	* gdb.base/nodebug.c: #include <stdint.h>.
	(multf, multf_noproto, mult, mult_noproto, add8, add8_noproto):
	New functions.
	* gdb.base/nodebug.exp (test_call_promotion): New procedure.
	Change expected output of print/whatis/ptype with functions with
	no debug info.  Test all supported languages.  Call
	test_call_promotion.
	* gdb.compile/compile.exp: Adjust expected output to expect
	warning.
	* gdb.threads/siginfo-threads.exp: Likewise.
2017-09-04 20:21:13 +01:00

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/* Support for printing Fortran types for GDB, the GNU debugger.
Copyright (C) 1986-2017 Free Software Foundation, Inc.
Contributed by Motorola. Adapted from the C version by Farooq Butt
(fmbutt@engage.sps.mot.com).
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 "gdb_obstack.h"
#include "bfd.h"
#include "symtab.h"
#include "gdbtypes.h"
#include "expression.h"
#include "value.h"
#include "gdbcore.h"
#include "target.h"
#include "f-lang.h"
#include "typeprint.h"
#if 0 /* Currently unused. */
static void f_type_print_args (struct type *, struct ui_file *);
#endif
static void f_type_print_varspec_suffix (struct type *, struct ui_file *, int,
int, int, int);
void f_type_print_varspec_prefix (struct type *, struct ui_file *,
int, int);
void f_type_print_base (struct type *, struct ui_file *, int, int);
/* LEVEL is the depth to indent lines by. */
void
f_print_type (struct type *type, const char *varstring, struct ui_file *stream,
int show, int level, const struct type_print_options *flags)
{
enum type_code code;
if (type_not_associated (type))
{
val_print_not_associated (stream);
return;
}
if (type_not_allocated (type))
{
val_print_not_allocated (stream);
return;
}
f_type_print_base (type, stream, show, level);
code = TYPE_CODE (type);
if ((varstring != NULL && *varstring != '\0')
/* Need a space if going to print stars or brackets;
but not if we will print just a type name. */
|| ((show > 0 || TYPE_NAME (type) == 0)
&& (code == TYPE_CODE_PTR || code == TYPE_CODE_FUNC
|| code == TYPE_CODE_METHOD
|| code == TYPE_CODE_ARRAY
|| code == TYPE_CODE_REF)))
fputs_filtered (" ", stream);
f_type_print_varspec_prefix (type, stream, show, 0);
if (varstring != NULL)
{
int demangled_args;
fputs_filtered (varstring, stream);
/* For demangled function names, we have the arglist as part of the name,
so don't print an additional pair of ()'s. */
demangled_args = (*varstring != '\0'
&& varstring[strlen (varstring) - 1] == ')');
f_type_print_varspec_suffix (type, stream, show, 0, demangled_args, 0);
}
}
/* Print any asterisks or open-parentheses needed before the
variable name (to describe its type).
On outermost call, pass 0 for PASSED_A_PTR.
On outermost call, SHOW > 0 means should ignore
any typename for TYPE and show its details.
SHOW is always zero on recursive calls. */
void
f_type_print_varspec_prefix (struct type *type, struct ui_file *stream,
int show, int passed_a_ptr)
{
if (type == 0)
return;
if (TYPE_NAME (type) && show <= 0)
return;
QUIT;
switch (TYPE_CODE (type))
{
case TYPE_CODE_PTR:
f_type_print_varspec_prefix (TYPE_TARGET_TYPE (type), stream, 0, 1);
break;
case TYPE_CODE_FUNC:
f_type_print_varspec_prefix (TYPE_TARGET_TYPE (type), stream, 0, 0);
if (passed_a_ptr)
fprintf_filtered (stream, "(");
break;
case TYPE_CODE_ARRAY:
f_type_print_varspec_prefix (TYPE_TARGET_TYPE (type), stream, 0, 0);
break;
case TYPE_CODE_UNDEF:
case TYPE_CODE_STRUCT:
case TYPE_CODE_UNION:
case TYPE_CODE_ENUM:
case TYPE_CODE_INT:
case TYPE_CODE_FLT:
case TYPE_CODE_VOID:
case TYPE_CODE_ERROR:
case TYPE_CODE_CHAR:
case TYPE_CODE_BOOL:
case TYPE_CODE_SET:
case TYPE_CODE_RANGE:
case TYPE_CODE_STRING:
case TYPE_CODE_METHOD:
case TYPE_CODE_REF:
case TYPE_CODE_COMPLEX:
case TYPE_CODE_TYPEDEF:
/* These types need no prefix. They are listed here so that
gcc -Wall will reveal any types that haven't been handled. */
break;
}
}
/* Print any array sizes, function arguments or close parentheses
needed after the variable name (to describe its type).
Args work like c_type_print_varspec_prefix. */
static void
f_type_print_varspec_suffix (struct type *type, struct ui_file *stream,
int show, int passed_a_ptr, int demangled_args,
int arrayprint_recurse_level)
{
int upper_bound, lower_bound;
/* No static variables are permitted as an error call may occur during
execution of this function. */
if (type == 0)
return;
if (TYPE_NAME (type) && show <= 0)
return;
QUIT;
switch (TYPE_CODE (type))
{
case TYPE_CODE_ARRAY:
arrayprint_recurse_level++;
if (arrayprint_recurse_level == 1)
fprintf_filtered (stream, "(");
if (type_not_associated (type))
val_print_not_associated (stream);
else if (type_not_allocated (type))
val_print_not_allocated (stream);
else
{
if (TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_ARRAY)
f_type_print_varspec_suffix (TYPE_TARGET_TYPE (type), stream, 0,
0, 0, arrayprint_recurse_level);
lower_bound = f77_get_lowerbound (type);
if (lower_bound != 1) /* Not the default. */
fprintf_filtered (stream, "%d:", lower_bound);
/* Make sure that, if we have an assumed size array, we
print out a warning and print the upperbound as '*'. */
if (TYPE_ARRAY_UPPER_BOUND_IS_UNDEFINED (type))
fprintf_filtered (stream, "*");
else
{
upper_bound = f77_get_upperbound (type);
fprintf_filtered (stream, "%d", upper_bound);
}
if (TYPE_CODE (TYPE_TARGET_TYPE (type)) != TYPE_CODE_ARRAY)
f_type_print_varspec_suffix (TYPE_TARGET_TYPE (type), stream, 0,
0, 0, arrayprint_recurse_level);
}
if (arrayprint_recurse_level == 1)
fprintf_filtered (stream, ")");
else
fprintf_filtered (stream, ",");
arrayprint_recurse_level--;
break;
case TYPE_CODE_PTR:
case TYPE_CODE_REF:
f_type_print_varspec_suffix (TYPE_TARGET_TYPE (type), stream, 0, 1, 0,
arrayprint_recurse_level);
fprintf_filtered (stream, ")");
break;
case TYPE_CODE_FUNC:
f_type_print_varspec_suffix (TYPE_TARGET_TYPE (type), stream, 0,
passed_a_ptr, 0, arrayprint_recurse_level);
if (passed_a_ptr)
fprintf_filtered (stream, ")");
fprintf_filtered (stream, "()");
break;
case TYPE_CODE_UNDEF:
case TYPE_CODE_STRUCT:
case TYPE_CODE_UNION:
case TYPE_CODE_ENUM:
case TYPE_CODE_INT:
case TYPE_CODE_FLT:
case TYPE_CODE_VOID:
case TYPE_CODE_ERROR:
case TYPE_CODE_CHAR:
case TYPE_CODE_BOOL:
case TYPE_CODE_SET:
case TYPE_CODE_RANGE:
case TYPE_CODE_STRING:
case TYPE_CODE_METHOD:
case TYPE_CODE_COMPLEX:
case TYPE_CODE_TYPEDEF:
/* These types do not need a suffix. They are listed so that
gcc -Wall will report types that may not have been considered. */
break;
}
}
/* Print the name of the type (or the ultimate pointer target,
function value or array element), or the description of a
structure or union.
SHOW nonzero means don't print this type as just its name;
show its real definition even if it has a name.
SHOW zero means print just typename or struct tag if there is one
SHOW negative means abbreviate structure elements.
SHOW is decremented for printing of structure elements.
LEVEL is the depth to indent by.
We increase it for some recursive calls. */
void
f_type_print_base (struct type *type, struct ui_file *stream, int show,
int level)
{
int upper_bound;
int index;
QUIT;
wrap_here (" ");
if (type == NULL)
{
fputs_filtered ("<type unknown>", stream);
return;
}
/* When SHOW is zero or less, and there is a valid type name, then always
just print the type name directly from the type. */
if ((show <= 0) && (TYPE_NAME (type) != NULL))
{
fprintfi_filtered (level, stream, "%s", TYPE_NAME (type));
return;
}
if (TYPE_CODE (type) != TYPE_CODE_TYPEDEF)
type = check_typedef (type);
switch (TYPE_CODE (type))
{
case TYPE_CODE_TYPEDEF:
f_type_print_base (TYPE_TARGET_TYPE (type), stream, 0, level);
break;
case TYPE_CODE_ARRAY:
f_type_print_base (TYPE_TARGET_TYPE (type), stream, show, level);
break;
case TYPE_CODE_FUNC:
if (TYPE_TARGET_TYPE (type) == NULL)
type_print_unknown_return_type (stream);
else
f_type_print_base (TYPE_TARGET_TYPE (type), stream, show, level);
break;
case TYPE_CODE_PTR:
fprintf_filtered (stream, "PTR TO -> ( ");
f_type_print_base (TYPE_TARGET_TYPE (type), stream, show, level);
break;
case TYPE_CODE_REF:
fprintf_filtered (stream, "REF TO -> ( ");
f_type_print_base (TYPE_TARGET_TYPE (type), stream, show, level);
break;
case TYPE_CODE_VOID:
fprintfi_filtered (level, stream, "VOID");
break;
case TYPE_CODE_UNDEF:
fprintfi_filtered (level, stream, "struct <unknown>");
break;
case TYPE_CODE_ERROR:
fprintfi_filtered (level, stream, "%s", TYPE_ERROR_NAME (type));
break;
case TYPE_CODE_RANGE:
/* This should not occur. */
fprintfi_filtered (level, stream, "<range type>");
break;
case TYPE_CODE_CHAR:
case TYPE_CODE_INT:
/* There may be some character types that attempt to come
through as TYPE_CODE_INT since dbxstclass.h is so
C-oriented, we must change these to "character" from "char". */
if (strcmp (TYPE_NAME (type), "char") == 0)
fprintfi_filtered (level, stream, "character");
else
goto default_case;
break;
case TYPE_CODE_STRING:
/* Strings may have dynamic upperbounds (lengths) like arrays. */
if (TYPE_ARRAY_UPPER_BOUND_IS_UNDEFINED (type))
fprintfi_filtered (level, stream, "character*(*)");
else
{
upper_bound = f77_get_upperbound (type);
fprintf_filtered (stream, "character*%d", upper_bound);
}
break;
case TYPE_CODE_STRUCT:
case TYPE_CODE_UNION:
if (TYPE_CODE (type) == TYPE_CODE_UNION)
fprintfi_filtered (level, stream, "Type, C_Union :: ");
else
fprintfi_filtered (level, stream, "Type ");
fputs_filtered (TYPE_TAG_NAME (type), stream);
/* According to the definition,
we only print structure elements in case show > 0. */
if (show > 0)
{
fputs_filtered ("\n", stream);
for (index = 0; index < TYPE_NFIELDS (type); index++)
{
f_type_print_base (TYPE_FIELD_TYPE (type, index), stream,
show - 1, level + 4);
fputs_filtered (" :: ", stream);
fputs_filtered (TYPE_FIELD_NAME (type, index), stream);
f_type_print_varspec_suffix (TYPE_FIELD_TYPE (type, index),
stream, show - 1, 0, 0, 0);
fputs_filtered ("\n", stream);
}
fprintfi_filtered (level, stream, "End Type ");
fputs_filtered (TYPE_TAG_NAME (type), stream);
}
break;
case TYPE_CODE_MODULE:
fprintfi_filtered (level, stream, "module %s", TYPE_TAG_NAME (type));
break;
default_case:
default:
/* Handle types not explicitly handled by the other cases,
such as fundamental types. For these, just print whatever
the type name is, as recorded in the type itself. If there
is no type name, then complain. */
if (TYPE_NAME (type) != NULL)
fprintfi_filtered (level, stream, "%s", TYPE_NAME (type));
else
error (_("Invalid type code (%d) in symbol table."), TYPE_CODE (type));
break;
}
}
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