diff mbox series

[v2] c++/modules: Fix dangling pointer with imported_temploid_friends

Message ID 6632edc2.170a0220.9abdd.00d3@mx.google.com
State New
Headers show
Series [v2] c++/modules: Fix dangling pointer with imported_temploid_friends | expand

Commit Message

Nathaniel Shead May 2, 2024, 1:34 a.m. UTC 
On Thu, May 02, 2024 at 12:15:44AM +1000, Nathaniel Shead wrote:
> On Wed, May 01, 2024 at 09:57:38AM -0400, Patrick Palka wrote:
> > 
> > On Wed, 1 May 2024, Nathaniel Shead wrote:
> > 
> > > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk (and
> > > later 14.2)?  I don't think making it a GTY root is necessary but I felt
> > > perhaps better to be safe than sorry.
> > > 
> > > Potentially another approach would be to use DECL_UID instead like how
> > > entity_map does; would that be preferable?
> > > 
> > > -- >8 --
> > > 
> > > I got notified by Linaro CI and by checking testresults that there seems
> > > to be some occasional failures in tpl-friend-4_b.C on some architectures
> > > and standards modes since r15-59-gb5f6a56940e708.  I haven't been able
> > > to reproduce but looking at the backtrace I suspect the issue is that
> > > we're adding to the 'imported_temploid_friend' map a decl that is
> > > ultimately discarded, which then has its address reused by a later decl
> > > causing a failure in the assert in 'set_originating_module'.
> > > 
> > > This patch attempts to fix the issue in two ways: by ensuring that we
> > > only store the decl if we know it's a new decl (and hence won't be
> > > discarded), and by making the imported_temploid_friends map a GTY root
> > > so that even if the decl does get discarded later the address isn't
> > > reused.
> > > 
> > > gcc/cp/ChangeLog:
> > > 
> > > 	* module.cc (imported_temploid_friends): Mark GTY, and...
> > > 	(init_modules): ...allocate from GGC.
> > > 	(trees_in::decl_value): Only write to imported_temploid_friends
> > > 	for new decls.
> > > 
> > > Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> > > ---
> > >  gcc/cp/module.cc | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> > > index 5b8ff5bc483..37d38bb9654 100644
> > > --- a/gcc/cp/module.cc
> > > +++ b/gcc/cp/module.cc
> > > @@ -2731,7 +2731,7 @@ static keyed_map_t *keyed_table;
> > >     need to be attached to the same module as the temploid.  This maps
> > >     these decls to the temploid they are instantiated them, as there is
> > >     no other easy way to get this information.  */
> > > -static hash_map<tree, tree> *imported_temploid_friends;
> > > +static GTY(()) hash_map<tree, tree> *imported_temploid_friends;
> > >  
> > >  /********************************************************************/
> > >  /* Tree streaming.   The tree streaming is very specific to the tree
> > > @@ -8327,7 +8327,8 @@ trees_in::decl_value ()
> > >    if (TREE_CODE (inner) == FUNCTION_DECL
> > >        || TREE_CODE (inner) == TYPE_DECL)
> > >      if (tree owner = tree_node ())
> > > -      imported_temploid_friends->put (decl, owner);
> > > +      if (is_new)
> > > +	imported_temploid_friends->put (decl, owner);
> > 
> > Hmm, I'm not seeing this code path getting reached for tpl-friend-4_b.C.
> > It seems we're instead adding to imported_temploid_friends from
> > propagate_defining_module, during tsubst_friend_function.
> > 
> > What seems to be happening is that we we first tsubst_friend_function
> > 'foo' from TPL<int>, and then we tsubst_friend_function 'foo' from DEF<int>,
> > which ends up calling duplicate_decls, which ggc_frees this 'foo'
> > redeclaration that is still present in the imported_temploid_friends map.
> > 
> > So I don't think marking imported_temploid_friends as a GC root would
> > help with this situation.  If we want to keep imported_temploid_friends
> > as a tree -> tree map, I think we just need to ensure that a decl
> > is removed from the map upon getting ggc_free'd from e.g.  duplicate_decls.
> > 
> > But it seems simpler to use DECL_UID as the key instead, since those
> > never get reused even after the decl gets ggc_free'd IIUC.
> > 
> 
> Ah right, thanks for digging into that further.  Yup OK, I think
> probably the DECL_UID route feels safer to me then in case there are
> other places where a decl might be explicitly freed.
> 
> Looking at tree.cc it looks like the relevant function is
> 'allocate_decl_uid' which shouldn't reuse UIDs until 2^32 decls have
> been created, so we should be safe on the reuse front.
> 
> I'll draft and test a patch for that tomorrow morning.
> 

Here's that patch. Bootstrapped and regtested on x86_64-pc-linux-gnu, OK
for trunk/14.2?

-- >8 --

I got notified by Linaro CI and by checking testresults that there seems
to be some occasional failures in tpl-friend-4_b.C on some architectures
and standards modes since r15-59-gb5f6a56940e708.  I haven't been able
to reproduce but looking at the backtrace I suspect the issue is that
we're adding to the 'imported_temploid_friend' map a decl that is
ultimately discarded, which then has its address reused by a later decl
causing a failure in the assert in 'set_originating_module'.

This patch fixes the problem by using DECL_UID as the map key instead of
the tree directly, much like with entity_map, since even if a
declaration gets deallocated the DECL_UID should not be reused by a
later declaration.

gcc/cp/ChangeLog:

	* module.cc (imported_temploid_friends): Map from DECL_UID
	instead of tree.
	(get_originating_module_decl): Likewise.
	(propagate_defining_module): Likewise.
	(trees_out::decl_value): Likewise.
	(trees_in::decl_value): Likewise. And only enter into the map
	for new declarations.
	(init_modules): Update type of imported_temploid_friends.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
---
 gcc/cp/module.cc | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

Comments

Patrick Palka May 2, 2024, 2:16 p.m. UTC | #1 
On Wed, May 1, 2024 at 9:35 PM Nathaniel Shead
<nathanieloshead@gmail.com> wrote:
>
> On Thu, May 02, 2024 at 12:15:44AM +1000, Nathaniel Shead wrote:
> > On Wed, May 01, 2024 at 09:57:38AM -0400, Patrick Palka wrote:
> > >
> > > On Wed, 1 May 2024, Nathaniel Shead wrote:
> > >
> > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk (and
> > > > later 14.2)?  I don't think making it a GTY root is necessary but I felt
> > > > perhaps better to be safe than sorry.
> > > >
> > > > Potentially another approach would be to use DECL_UID instead like how
> > > > entity_map does; would that be preferable?
> > > >
> > > > -- >8 --
> > > >
> > > > I got notified by Linaro CI and by checking testresults that there seems
> > > > to be some occasional failures in tpl-friend-4_b.C on some architectures
> > > > and standards modes since r15-59-gb5f6a56940e708.  I haven't been able
> > > > to reproduce but looking at the backtrace I suspect the issue is that
> > > > we're adding to the 'imported_temploid_friend' map a decl that is
> > > > ultimately discarded, which then has its address reused by a later decl
> > > > causing a failure in the assert in 'set_originating_module'.
> > > >
> > > > This patch attempts to fix the issue in two ways: by ensuring that we
> > > > only store the decl if we know it's a new decl (and hence won't be
> > > > discarded), and by making the imported_temploid_friends map a GTY root
> > > > so that even if the decl does get discarded later the address isn't
> > > > reused.
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > >   * module.cc (imported_temploid_friends): Mark GTY, and...
> > > >   (init_modules): ...allocate from GGC.
> > > >   (trees_in::decl_value): Only write to imported_temploid_friends
> > > >   for new decls.
> > > >
> > > > Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> > > > ---
> > > >  gcc/cp/module.cc | 7 ++++---
> > > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> > > > index 5b8ff5bc483..37d38bb9654 100644
> > > > --- a/gcc/cp/module.cc
> > > > +++ b/gcc/cp/module.cc
> > > > @@ -2731,7 +2731,7 @@ static keyed_map_t *keyed_table;
> > > >     need to be attached to the same module as the temploid.  This maps
> > > >     these decls to the temploid they are instantiated them, as there is
> > > >     no other easy way to get this information.  */
> > > > -static hash_map<tree, tree> *imported_temploid_friends;
> > > > +static GTY(()) hash_map<tree, tree> *imported_temploid_friends;
> > > >
> > > >  /********************************************************************/
> > > >  /* Tree streaming.   The tree streaming is very specific to the tree
> > > > @@ -8327,7 +8327,8 @@ trees_in::decl_value ()
> > > >    if (TREE_CODE (inner) == FUNCTION_DECL
> > > >        || TREE_CODE (inner) == TYPE_DECL)
> > > >      if (tree owner = tree_node ())
> > > > -      imported_temploid_friends->put (decl, owner);
> > > > +      if (is_new)
> > > > + imported_temploid_friends->put (decl, owner);
> > >
> > > Hmm, I'm not seeing this code path getting reached for tpl-friend-4_b.C.
> > > It seems we're instead adding to imported_temploid_friends from
> > > propagate_defining_module, during tsubst_friend_function.
> > >
> > > What seems to be happening is that we we first tsubst_friend_function
> > > 'foo' from TPL<int>, and then we tsubst_friend_function 'foo' from DEF<int>,
> > > which ends up calling duplicate_decls, which ggc_frees this 'foo'
> > > redeclaration that is still present in the imported_temploid_friends map.
> > >
> > > So I don't think marking imported_temploid_friends as a GC root would
> > > help with this situation.  If we want to keep imported_temploid_friends
> > > as a tree -> tree map, I think we just need to ensure that a decl
> > > is removed from the map upon getting ggc_free'd from e.g.  duplicate_decls.
> > >
> > > But it seems simpler to use DECL_UID as the key instead, since those
> > > never get reused even after the decl gets ggc_free'd IIUC.
> > >
> >
> > Ah right, thanks for digging into that further.  Yup OK, I think
> > probably the DECL_UID route feels safer to me then in case there are
> > other places where a decl might be explicitly freed.
> >
> > Looking at tree.cc it looks like the relevant function is
> > 'allocate_decl_uid' which shouldn't reuse UIDs until 2^32 decls have
> > been created, so we should be safe on the reuse front.
> >
> > I'll draft and test a patch for that tomorrow morning.
> >
>
> Here's that patch. Bootstrapped and regtested on x86_64-pc-linux-gnu, OK
> for trunk/14.2?

LGTM


>
> -- >8 --
>
> I got notified by Linaro CI and by checking testresults that there seems
> to be some occasional failures in tpl-friend-4_b.C on some architectures
> and standards modes since r15-59-gb5f6a56940e708.  I haven't been able
> to reproduce but looking at the backtrace I suspect the issue is that
> we're adding to the 'imported_temploid_friend' map a decl that is
> ultimately discarded, which then has its address reused by a later decl
> causing a failure in the assert in 'set_originating_module'.
>
> This patch fixes the problem by using DECL_UID as the map key instead of
> the tree directly, much like with entity_map, since even if a
> declaration gets deallocated the DECL_UID should not be reused by a
> later declaration.
>
> gcc/cp/ChangeLog:
>
>         * module.cc (imported_temploid_friends): Map from DECL_UID
>         instead of tree.
>         (get_originating_module_decl): Likewise.
>         (propagate_defining_module): Likewise.
>         (trees_out::decl_value): Likewise.
>         (trees_in::decl_value): Likewise. And only enter into the map
>         for new declarations.
>         (init_modules): Update type of imported_temploid_friends.
>
> Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> ---
>  gcc/cp/module.cc | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index fac0301d80e..ceb383ba509 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -2730,8 +2730,13 @@ static keyed_map_t *keyed_table;
>  /* Instantiations of temploid friends imported from another module
>     need to be attached to the same module as the temploid.  This maps
>     these decls to the temploid they are instantiated them, as there is
> -   no other easy way to get this information.  */
> -static hash_map<tree, tree> *imported_temploid_friends;
> +   no other easy way to get this information.  We map the DECL_UID
> +   instead of the tree directly to handle keys that get freed and
> +   reused.  */
> +typedef hash_map<unsigned, tree,
> +                simple_hashmap_traits<int_hash<unsigned, 0>, tree>
> +                > temploid_map_t;
> +static temploid_map_t *imported_temploid_friends;
>
>  /********************************************************************/
>  /* Tree streaming.   The tree streaming is very specific to the tree
> @@ -7829,7 +7834,7 @@ trees_out::decl_value (tree decl, depset *dep)
>               /* But don't consider imported temploid friends as attached,
>                  since importers will need to merge this decl even if it was
>                  attached to a different module.  */
> -             if (imported_temploid_friends->get (decl))
> +             if (imported_temploid_friends->get (DECL_UID (decl)))
>                 is_attached = false;
>
>               bits.b (is_attached);
> @@ -8014,7 +8019,7 @@ trees_out::decl_value (tree decl, depset *dep)
>      {
>        /* Write imported temploid friends so that importers can reconstruct
>          this information on stream-in.  */
> -      tree* slot = imported_temploid_friends->get (decl);
> +      tree* slot = imported_temploid_friends->get (DECL_UID (decl));
>        tree_node (slot ? *slot : NULL_TREE);
>      }
>
> @@ -8327,7 +8332,8 @@ trees_in::decl_value ()
>    if (TREE_CODE (inner) == FUNCTION_DECL
>        || TREE_CODE (inner) == TYPE_DECL)
>      if (tree owner = tree_node ())
> -      imported_temploid_friends->put (decl, owner);
> +      if (is_new)
> +       imported_temploid_friends->put (DECL_UID (decl), owner);
>
>    /* Regular typedefs will have a NULL TREE_TYPE at this point.  */
>    unsigned tdef_flags = 0;
> @@ -18976,7 +18982,7 @@ get_originating_module_decl (tree decl)
>        /* An imported temploid friend is attached to the same module the
>          befriending class was.  */
>        if (imported_temploid_friends)
> -       if (tree *slot = imported_temploid_friends->get (decl))
> +       if (tree *slot = imported_temploid_friends->get (DECL_UID (decl)))
>           decl = *slot;
>
>        int use;
> @@ -19306,7 +19312,7 @@ propagate_defining_module (tree decl, tree orig)
>
>    if (DECL_LANG_SPECIFIC (not_tmpl) && DECL_MODULE_IMPORT_P (not_tmpl))
>      {
> -      bool exists = imported_temploid_friends->put (decl, orig);
> +      bool exists = imported_temploid_friends->put (DECL_UID (decl), orig);
>
>        /* We should only be called if lookup for an existing decl
>          failed, in which case there shouldn't already be an entry
> @@ -20528,8 +20534,7 @@ init_modules (cpp_reader *reader)
>        pending_table = new pending_map_t (EXPERIMENT (1, 400));
>        entity_map = new entity_map_t (EXPERIMENT (1, 400));
>        vec_safe_reserve (entity_ary, EXPERIMENT (1, 400));
> -      imported_temploid_friends
> -       = new hash_map<tree,tree> (EXPERIMENT (1, 400));
> +      imported_temploid_friends = new temploid_map_t (EXPERIMENT (1, 400));
>      }
>
>  #if CHECKING_P
> --
> 2.43.2
>
Jason Merrill May 2, 2024, 6:05 p.m. UTC | #2 
On 5/1/24 21:34, Nathaniel Shead wrote:
> On Thu, May 02, 2024 at 12:15:44AM +1000, Nathaniel Shead wrote:
>> On Wed, May 01, 2024 at 09:57:38AM -0400, Patrick Palka wrote:
>>>
>>> On Wed, 1 May 2024, Nathaniel Shead wrote:
>>>
>>>> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk (and
>>>> later 14.2)?  I don't think making it a GTY root is necessary but I felt
>>>> perhaps better to be safe than sorry.
>>>>
>>>> Potentially another approach would be to use DECL_UID instead like how
>>>> entity_map does; would that be preferable?
>>>>
>>>> -- >8 --
>>>>
>>>> I got notified by Linaro CI and by checking testresults that there seems
>>>> to be some occasional failures in tpl-friend-4_b.C on some architectures
>>>> and standards modes since r15-59-gb5f6a56940e708.  I haven't been able
>>>> to reproduce but looking at the backtrace I suspect the issue is that
>>>> we're adding to the 'imported_temploid_friend' map a decl that is
>>>> ultimately discarded, which then has its address reused by a later decl
>>>> causing a failure in the assert in 'set_originating_module'.
>>>>
>>>> This patch attempts to fix the issue in two ways: by ensuring that we
>>>> only store the decl if we know it's a new decl (and hence won't be
>>>> discarded), and by making the imported_temploid_friends map a GTY root
>>>> so that even if the decl does get discarded later the address isn't
>>>> reused.
>>>>
>>>> gcc/cp/ChangeLog:
>>>>
>>>> 	* module.cc (imported_temploid_friends): Mark GTY, and...
>>>> 	(init_modules): ...allocate from GGC.
>>>> 	(trees_in::decl_value): Only write to imported_temploid_friends
>>>> 	for new decls.
>>>>
>>>> Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
>>>> ---
>>>>   gcc/cp/module.cc | 7 ++++---
>>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
>>>> index 5b8ff5bc483..37d38bb9654 100644
>>>> --- a/gcc/cp/module.cc
>>>> +++ b/gcc/cp/module.cc
>>>> @@ -2731,7 +2731,7 @@ static keyed_map_t *keyed_table;
>>>>      need to be attached to the same module as the temploid.  This maps
>>>>      these decls to the temploid they are instantiated them, as there is
>>>>      no other easy way to get this information.  */
>>>> -static hash_map<tree, tree> *imported_temploid_friends;
>>>> +static GTY(()) hash_map<tree, tree> *imported_temploid_friends;
>>>>   
>>>>   /********************************************************************/
>>>>   /* Tree streaming.   The tree streaming is very specific to the tree
>>>> @@ -8327,7 +8327,8 @@ trees_in::decl_value ()
>>>>     if (TREE_CODE (inner) == FUNCTION_DECL
>>>>         || TREE_CODE (inner) == TYPE_DECL)
>>>>       if (tree owner = tree_node ())
>>>> -      imported_temploid_friends->put (decl, owner);
>>>> +      if (is_new)
>>>> +	imported_temploid_friends->put (decl, owner);
>>>
>>> Hmm, I'm not seeing this code path getting reached for tpl-friend-4_b.C.
>>> It seems we're instead adding to imported_temploid_friends from
>>> propagate_defining_module, during tsubst_friend_function.
>>>
>>> What seems to be happening is that we we first tsubst_friend_function
>>> 'foo' from TPL<int>, and then we tsubst_friend_function 'foo' from DEF<int>,
>>> which ends up calling duplicate_decls, which ggc_frees this 'foo'
>>> redeclaration that is still present in the imported_temploid_friends map.
>>>
>>> So I don't think marking imported_temploid_friends as a GC root would
>>> help with this situation.  If we want to keep imported_temploid_friends
>>> as a tree -> tree map, I think we just need to ensure that a decl
>>> is removed from the map upon getting ggc_free'd from e.g.  duplicate_decls.

Could we instead move the call to propagate_defining_module down a few 
lines, after the pushdecl?

>>> But it seems simpler to use DECL_UID as the key instead, since those
>>> never get reused even after the decl gets ggc_free'd IIUC.

It still means garbage entries in the hash_map, which is undesirable 
even if it doesn't cause the same kind of breakage.

Incidentally, decl_tree_map is preferable to hash_map<tree,tree> when 
the key is always a decl.

Jason
diff mbox series

Patch

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index fac0301d80e..ceb383ba509 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -2730,8 +2730,13 @@  static keyed_map_t *keyed_table;
 /* Instantiations of temploid friends imported from another module
    need to be attached to the same module as the temploid.  This maps
    these decls to the temploid they are instantiated them, as there is
-   no other easy way to get this information.  */
-static hash_map<tree, tree> *imported_temploid_friends;
+   no other easy way to get this information.  We map the DECL_UID
+   instead of the tree directly to handle keys that get freed and
+   reused.  */
+typedef hash_map<unsigned, tree,
+		 simple_hashmap_traits<int_hash<unsigned, 0>, tree>
+		 > temploid_map_t;
+static temploid_map_t *imported_temploid_friends;
 
 /********************************************************************/
 /* Tree streaming.   The tree streaming is very specific to the tree
@@ -7829,7 +7834,7 @@  trees_out::decl_value (tree decl, depset *dep)
 	      /* But don't consider imported temploid friends as attached,
 		 since importers will need to merge this decl even if it was
 		 attached to a different module.  */
-	      if (imported_temploid_friends->get (decl))
+	      if (imported_temploid_friends->get (DECL_UID (decl)))
 		is_attached = false;
 
 	      bits.b (is_attached);
@@ -8014,7 +8019,7 @@  trees_out::decl_value (tree decl, depset *dep)
     {
       /* Write imported temploid friends so that importers can reconstruct
 	 this information on stream-in.  */
-      tree* slot = imported_temploid_friends->get (decl);
+      tree* slot = imported_temploid_friends->get (DECL_UID (decl));
       tree_node (slot ? *slot : NULL_TREE);
     }
 
@@ -8327,7 +8332,8 @@  trees_in::decl_value ()
   if (TREE_CODE (inner) == FUNCTION_DECL
       || TREE_CODE (inner) == TYPE_DECL)
     if (tree owner = tree_node ())
-      imported_temploid_friends->put (decl, owner);
+      if (is_new)
+	imported_temploid_friends->put (DECL_UID (decl), owner);
 
   /* Regular typedefs will have a NULL TREE_TYPE at this point.  */
   unsigned tdef_flags = 0;
@@ -18976,7 +18982,7 @@  get_originating_module_decl (tree decl)
       /* An imported temploid friend is attached to the same module the
 	 befriending class was.  */
       if (imported_temploid_friends)
-	if (tree *slot = imported_temploid_friends->get (decl))
+	if (tree *slot = imported_temploid_friends->get (DECL_UID (decl)))
 	  decl = *slot;
 
       int use;
@@ -19306,7 +19312,7 @@  propagate_defining_module (tree decl, tree orig)
 
   if (DECL_LANG_SPECIFIC (not_tmpl) && DECL_MODULE_IMPORT_P (not_tmpl))
     {
-      bool exists = imported_temploid_friends->put (decl, orig);
+      bool exists = imported_temploid_friends->put (DECL_UID (decl), orig);
 
       /* We should only be called if lookup for an existing decl
 	 failed, in which case there shouldn't already be an entry
@@ -20528,8 +20534,7 @@  init_modules (cpp_reader *reader)
       pending_table = new pending_map_t (EXPERIMENT (1, 400));
       entity_map = new entity_map_t (EXPERIMENT (1, 400));
       vec_safe_reserve (entity_ary, EXPERIMENT (1, 400));
-      imported_temploid_friends
-	= new hash_map<tree,tree> (EXPERIMENT (1, 400));
+      imported_temploid_friends = new temploid_map_t (EXPERIMENT (1, 400));
     }
 
 #if CHECKING_P