Re: [RFC PATCH 0/3] Pretty-printing for errno

[Pedro Alves <palves at redhat dot com>]

On 06/29/2017 04:48 PM, Phil Muldoon wrote:
> 
> (gdb) p (test_i) i
> $2 = ('typename: ', 'int')
> 
> Which is most puzzling.

Indeed.  No need for printers to see this, actually.

With this code:

 typedef int zzz;
 zzz z;

gdb:

 (gdb) whatis z
 type = zzz
 (gdb) whatis (zzz) z
 type = int

Eh.

I suspect this is the result of a bogus implementation of
only stripping one level of typedef if the argument to
whatis is a type name.  From the manual:

 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 comes from 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 is reachable in both:

#1 - (gdb) whatis (zzz)0
#2 - (gdb) whatis zzz

While only case #2 should strip the typedef.  Removing that "find immediate
target" code above help with fixing #1.  We then run into the fact that
value_cast also drops typedefs.  Fixing that (see patch below) makes
whatis (zzz)0 work as expected:

 (gdb) whatis (zzz)0
 type = zzz

however, we'd need to still make "whatis" strip one level of
typedefs when the argument is a type, somehow, because we now
get this:

 (gdb) whatis zzz
 type = zzz
>From 21f3a88611fad22f73aff2217c93d99971dd076f Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Thu, 29 Jun 2017 17:18:32 +0100
Subject: [PATCH] whatis

---
 gdb/eval.c   |  2 ++
 gdb/valops.c | 28 +++++++++++++++-------------
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/gdb/eval.c b/gdb/eval.c
index 2a39774..6aa2499 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -2735,8 +2735,10 @@ evaluate_subexp_standard (struct type *expect_type,
 	     result because we do not want to dig past all
 	     typedefs.  */
 	  check_typedef (type);
+#if 0
 	  if (TYPE_CODE (type) == TYPE_CODE_TYPEDEF)
 	    type = TYPE_TARGET_TYPE (type);
+#endif
 	  return allocate_value (type);
 	}
       else
diff --git a/gdb/valops.c b/gdb/valops.c
index 8675e6c..058fe1e 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -378,6 +378,8 @@ value_cast (struct type *type, struct value *arg2)
     /* We deref the value and then do the cast.  */
     return value_cast (type, coerce_ref (arg2)); 
 
+  struct type *org_type = type;
+
   type = check_typedef (type);
   code1 = TYPE_CODE (type);
   arg2 = coerce_ref (arg2);
@@ -452,14 +454,14 @@ value_cast (struct type *type, struct value *arg2)
       && (code2 == TYPE_CODE_STRUCT || code2 == TYPE_CODE_UNION)
       && TYPE_NAME (type) != 0)
     {
-      struct value *v = value_cast_structs (type, arg2);
+      struct value *v = value_cast_structs (org_type, arg2);
 
       if (v)
 	return v;
     }
 
   if (code1 == TYPE_CODE_FLT && scalar)
-    return value_from_double (type, value_as_double (arg2));
+    return value_from_double (org_type, value_as_double (arg2));
   else if (code1 == TYPE_CODE_DECFLOAT && scalar)
     {
       enum bfd_endian byte_order = gdbarch_byte_order (get_type_arch (type));
@@ -475,7 +477,7 @@ value_cast (struct type *type, struct value *arg2)
 	/* The only option left is an integral type.  */
 	decimal_from_integral (arg2, dec, dec_len, byte_order);
 
-      return value_from_decfloat (type, dec);
+      return value_from_decfloat (org_type, dec);
     }
   else if ((code1 == TYPE_CODE_INT || code1 == TYPE_CODE_ENUM
 	    || code1 == TYPE_CODE_RANGE)
@@ -496,7 +498,7 @@ value_cast (struct type *type, struct value *arg2)
 		     gdbarch_byte_order (get_type_arch (type2)));
       else
         longest = value_as_long (arg2);
-      return value_from_longest (type, convert_to_boolean ?
+      return value_from_longest (org_type, convert_to_boolean ?
 				 (LONGEST) (longest ? 1 : 0) : longest);
     }
   else if (code1 == TYPE_CODE_PTR && (code2 == TYPE_CODE_INT  
@@ -522,14 +524,14 @@ value_cast (struct type *type, struct value *arg2)
 	      || longest <= -((LONGEST) 1 << addr_bit))
 	    warning (_("value truncated"));
 	}
-      return value_from_longest (type, longest);
+      return value_from_longest (org_type, longest);
     }
   else if (code1 == TYPE_CODE_METHODPTR && code2 == TYPE_CODE_INT
 	   && value_as_long (arg2) == 0)
     {
-      struct value *result = allocate_value (type);
+      struct value *result = allocate_value (org_type);
 
-      cplus_make_method_ptr (type, value_contents_writeable (result), 0, 0);
+      cplus_make_method_ptr (org_type, value_contents_writeable (result), 0, 0);
       return result;
     }
   else if (code1 == TYPE_CODE_MEMBERPTR && code2 == TYPE_CODE_INT
@@ -537,7 +539,7 @@ value_cast (struct type *type, struct value *arg2)
     {
       /* The Itanium C++ ABI represents NULL pointers to members as
 	 minus one, instead of biasing the normal case.  */
-      return value_from_longest (type, -1);
+      return value_from_longest (org_type, -1);
     }
   else if (code1 == TYPE_CODE_ARRAY && TYPE_VECTOR (type)
 	   && code2 == TYPE_CODE_ARRAY && TYPE_VECTOR (type2)
@@ -548,21 +550,21 @@ value_cast (struct type *type, struct value *arg2)
     error (_("can only cast scalar to vector of same size"));
   else if (code1 == TYPE_CODE_VOID)
     {
-      return value_zero (type, not_lval);
+      return value_zero (org_type, not_lval);
     }
   else if (TYPE_LENGTH (type) == TYPE_LENGTH (type2))
     {
       if (code1 == TYPE_CODE_PTR && code2 == TYPE_CODE_PTR)
-	return value_cast_pointers (type, arg2, 0);
+	return value_cast_pointers (org_type, arg2, 0);
 
       arg2 = value_copy (arg2);
-      deprecated_set_value_type (arg2, type);
-      set_value_enclosing_type (arg2, type);
+      deprecated_set_value_type (arg2, org_type);
+      set_value_enclosing_type (arg2, org_type);
       set_value_pointed_to_offset (arg2, 0);	/* pai: chk_val */
       return arg2;
     }
   else if (VALUE_LVAL (arg2) == lval_memory)
-    return value_at_lazy (type, value_address (arg2));
+    return value_at_lazy (org_type, value_address (arg2));
   else
     {
       error (_("Invalid cast."));
-- 
2.5.5