Re: [PATCH] libiberty: Initialize d_printing in all cplus_demangle_* functions.

[Pedro Alves <palves@redhat.com>]

On 03/13/2017 08:35 PM, Mark Wielaard wrote:
> Switching mailinglist from gcc to gdb.
> 
> On Mon, 2017-03-13 at 18:54 +0000, Pedro Alves wrote:
>> On 03/13/2017 06:29 PM, Mark Wielaard wrote:
>>
>> Should gdb be memsetting instead to avoid having to know about
>> libiberty's "internals"?
> 
> Maybe. But I went with the version I tested.

Thanks, this restores master to a working state quickly.

> Basically none of this would be needed if gdb only used the
> cplus_demangle_fill_* functions to initialize the data structures
> (although that is where there was a bug, but that is now fixed).
> 
> cp-name-parser.y however sometimes uses the cplus_demangle_fill
> functions, but other times fills in the data structures by hand (using
> its own partial fill function make_empty). I know too little of this
> code to know why. Maybe the set of cplus_demangle_fill functions isn't
> complete enough or maybe the way the parser works not all information
> needed is there yet to call cplus_demangle_fill or maybe doing it by
> hand just felt more efficient?

I don't know either.  I have never had to look much deeply into this file.
Git blame points at the commit that added the parser in the first
place (git fb4c6eba):

 https://sourceware.org/ml/gdb-patches/2005-03/msg00182.html

But that doesn't include any comment about this either.

Seems like all uses of GDB's make_empty are followed by referring to
the "s_binary" union member via these two macros:

 #define d_left(dc) (dc)->u.s_binary.left
 #define d_right(dc) (dc)->u.s_binary.right

"s_binary" is documented as being "for other types":

struct demangle_component
{
...
    /* For other types.  */
    struct
    {
      /* Left (or only) subtree.  */
      struct demangle_component *left;
      /* Right subtree.  */
      struct demangle_component *right;
    } s_binary;

And there's a cplus_demangle_fill_component function to fill
these in.  It's already used by cp-name-parser.y in other
cases, via the fill_comp wrapper function.

Using that seems to work, testing the patch below on x86_64 Fedora 23
shows no regressions.

From e55453c67bbe772ce001ea15b152f8dc44b8945e Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Mon, 13 Mar 2017 22:54:09 +0000
Subject: [PATCH] gdb/cp-name-parser.y: Eliminate make_empty, use
 cplus_demangle_fill_component

The demangler exports the cplus_demangle_fill_component function that
clients should use to initialize demangle_component components that
use the "s_binary" union member.  cp-name-parser.y uses it in some
places, via the fill_comp wrapper, but not all.  Several places
instead use a GDB-specific "make_empty" function.  Because this
function does not call any of the demangler "fill" functions, we had
to patch it recently to clear the allocated demangle_component's
"d_printing" field, which is supposedly a "private" demangler field.
To avoid such problems in the future, this commit switches those
places to use "fill_comp" instead, and eliminates the "make_empty"
function.

gdb/ChangeLog:
2017-03-13  Pedro Alves  <palves@redhat.com>

	* cp-name-parser.y (make_empty): Delete.
	(demangler_special, nested_name, ptr_operator, array_indicator)
	(direct_declarator, declarator_1): Use fill_comp instead of
	make_empty.
---
 gdb/cp-name-parser.y | 57 ++++++++++++----------------------------------------
 1 file changed, 13 insertions(+), 44 deletions(-)

diff --git a/gdb/cp-name-parser.y b/gdb/cp-name-parser.y
index 70790fc..5a9e51c 100644
--- a/gdb/cp-name-parser.y
+++ b/gdb/cp-name-parser.y
@@ -197,15 +197,6 @@ fill_comp (enum demangle_component_type d_type, struct demangle_component *lhs,
 }
 
 static struct demangle_component *
-make_empty (enum demangle_component_type d_type)
-{
-  struct demangle_component *ret = d_grab ();
-  ret->type = d_type;
-  ret->d_printing = 0;
-  return ret;
-}
-
-static struct demangle_component *
 make_operator (const char *name, int args)
 {
   struct demangle_component *ret = d_grab ();
@@ -433,9 +424,7 @@ function
 
 demangler_special
 		:	DEMANGLER_SPECIAL start
-			{ $$ = make_empty ((enum demangle_component_type) $1);
-			  d_left ($$) = $2;
-			  d_right ($$) = NULL; }
+			{ $$ = fill_comp ((enum demangle_component_type) $1, $2, NULL); }
 		|	CONSTRUCTION_VTABLE start CONSTRUCTION_IN start
 			{ $$ = fill_comp (DEMANGLE_COMPONENT_CONSTRUCTION_VTABLE, $2, $4); }
 		;
@@ -600,30 +589,22 @@ ext_only_name	:	nested_name unqualified_name
 		;
 
 nested_name	:	NAME COLONCOLON
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_QUAL_NAME);
-			  d_left ($$.comp) = $1;
-			  d_right ($$.comp) = NULL;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_QUAL_NAME, $1, NULL);
 			  $$.last = $$.comp;
 			}
 		|	nested_name NAME COLONCOLON
 			{ $$.comp = $1.comp;
-			  d_right ($1.last) = make_empty (DEMANGLE_COMPONENT_QUAL_NAME);
+			  d_right ($1.last) = fill_comp (DEMANGLE_COMPONENT_QUAL_NAME, $2, NULL);
 			  $$.last = d_right ($1.last);
-			  d_left ($$.last) = $2;
-			  d_right ($$.last) = NULL;
 			}
 		|	templ COLONCOLON
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_QUAL_NAME);
-			  d_left ($$.comp) = $1;
-			  d_right ($$.comp) = NULL;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_QUAL_NAME, $1, NULL);
 			  $$.last = $$.comp;
 			}
 		|	nested_name templ COLONCOLON
 			{ $$.comp = $1.comp;
-			  d_right ($1.last) = make_empty (DEMANGLE_COMPONENT_QUAL_NAME);
+			  d_right ($1.last) = fill_comp (DEMANGLE_COMPONENT_QUAL_NAME, $2, NULL);
 			  $$.last = d_right ($1.last);
-			  d_left ($$.last) = $2;
-			  d_right ($$.last) = NULL;
 			}
 		;
 
@@ -761,41 +742,31 @@ builtin_type	:	int_seq
 		;
 
 ptr_operator	:	'*' qualifiers_opt
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_POINTER);
-			  $$.comp->u.s_binary.left = $$.comp->u.s_binary.right = NULL;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_POINTER, NULL, NULL);
 			  $$.last = &d_left ($$.comp);
 			  $$.comp = d_qualify ($$.comp, $2, 0); }
 		/* g++ seems to allow qualifiers after the reference?  */
 		|	'&'
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_REFERENCE);
-			  $$.comp->u.s_binary.left = $$.comp->u.s_binary.right = NULL;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_REFERENCE, NULL, NULL);
 			  $$.last = &d_left ($$.comp); }
 		|	nested_name '*' qualifiers_opt
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_PTRMEM_TYPE);
-			  $$.comp->u.s_binary.left = $1.comp;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_PTRMEM_TYPE, $1.comp, NULL);
 			  /* Convert the innermost DEMANGLE_COMPONENT_QUAL_NAME to a DEMANGLE_COMPONENT_NAME.  */
 			  *$1.last = *d_left ($1.last);
-			  $$.comp->u.s_binary.right = NULL;
 			  $$.last = &d_right ($$.comp);
 			  $$.comp = d_qualify ($$.comp, $3, 0); }
 		|	COLONCOLON nested_name '*' qualifiers_opt
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_PTRMEM_TYPE);
-			  $$.comp->u.s_binary.left = $2.comp;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_PTRMEM_TYPE, $2.comp, NULL);
 			  /* Convert the innermost DEMANGLE_COMPONENT_QUAL_NAME to a DEMANGLE_COMPONENT_NAME.  */
 			  *$2.last = *d_left ($2.last);
-			  $$.comp->u.s_binary.right = NULL;
 			  $$.last = &d_right ($$.comp);
 			  $$.comp = d_qualify ($$.comp, $4, 0); }
 		;
 
 array_indicator	:	'[' ']'
-			{ $$ = make_empty (DEMANGLE_COMPONENT_ARRAY_TYPE);
-			  d_left ($$) = NULL;
-			}
+			{ $$ = fill_comp (DEMANGLE_COMPONENT_ARRAY_TYPE, NULL, NULL); }
 		|	'[' INT ']'
-			{ $$ = make_empty (DEMANGLE_COMPONENT_ARRAY_TYPE);
-			  d_left ($$) = $2;
-			}
+			{ $$ = fill_comp (DEMANGLE_COMPONENT_ARRAY_TYPE, $2, NULL); }
 		;
 
 /* Details of this approach inspired by the G++ < 3.4 parser.  */
@@ -948,8 +919,7 @@ direct_declarator
 			  $$.last = &d_right ($2);
 			}
 		|	colon_ext_name
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_TYPED_NAME);
-			  d_left ($$.comp) = $1;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_TYPED_NAME, $1, NULL);
 			  $$.last = &d_right ($$.comp);
 			}
 		;
@@ -965,8 +935,7 @@ declarator_1	:	ptr_operator declarator_1
 			  $$.last = $1.last;
 			  *$2.last = $1.comp; }
 		|	colon_ext_name
-			{ $$.comp = make_empty (DEMANGLE_COMPONENT_TYPED_NAME);
-			  d_left ($$.comp) = $1;
+			{ $$.comp = fill_comp (DEMANGLE_COMPONENT_TYPED_NAME, $1, NULL);
 			  $$.last = &d_right ($$.comp);
 			}
 		|	direct_declarator_1
-- 
2.5.5