Re: [PATCH v3] c++/modules: Fix dangling pointer with imported_temploid_friends
On 5/6/24 18:53, Patrick Palka wrote: On Mon, 6 May 2024, Jason Merrill wrote: On 5/3/24 07:17, Nathaniel Shead wrote: On Thu, May 02, 2024 at 02:05:38PM -0400, Jason Merrill wrote: 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 --- 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 *imported_temploid_friends; +static GTY(()) hash_map *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, and then we tsubst_friend_function 'foo' from DEF, 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? Doing that for tsubst_friend_class seems to work OK with my current test cases, but for tsubst_friend_function doing so causes ICEs in 'module_may_redeclare' within duplicate_decls because the function is already marked as attached but the originating module information hasn't been setup yet. It's unfortunate that we need to add a hash table entry in order to make it through duplicate_decls, at which point it becomes dead. Ah, well. I suppose with tsubst_friend_class it works though because we can't ever take the pushdecl branch if an existing type exists that we would call duplicate_decls on. 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 when the key is always a decl. Ah thanks, didn't know about decl_tree_map. I feel that I prefer using DECL_UIDs explicitly here though; it's also consistent with the existing usage in entity_map_t, and it looks like decl_tree_map is still perhaps vulnerable to the original issue here (since DECL_UID is only used for hashing and not for equality, it looks like?). Though that said, 'decl_constraints' in constraints.cc seems to be using it fine (well
Re: [PATCH v3] c++/modules: Fix dangling pointer with imported_temploid_friends
On Mon, 6 May 2024, Jason Merrill wrote: > On 5/3/24 07:17, Nathaniel Shead wrote: > > On Thu, May 02, 2024 at 02:05:38PM -0400, Jason Merrill wrote: > > > 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 > > > > > > > --- > > > > > > >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 *imported_temploid_friends; > > > > > > > +static GTY(()) hash_map *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, and then we tsubst_friend_function 'foo' from > > > > > > DEF, > > > > > > 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? > > > > Doing that for tsubst_friend_class seems to work OK with my current test > > cases, but for tsubst_friend_function doing so causes ICE
Re: [PATCH v3] c++/modules: Fix dangling pointer with imported_temploid_friends
On 5/3/24 07:17, Nathaniel Shead wrote: On Thu, May 02, 2024 at 02:05:38PM -0400, Jason Merrill wrote: 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 --- 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 *imported_temploid_friends; +static GTY(()) hash_map *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, and then we tsubst_friend_function 'foo' from DEF, 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? Doing that for tsubst_friend_class seems to work OK with my current test cases, but for tsubst_friend_function doing so causes ICEs in 'module_may_redeclare' within duplicate_decls because the function is already marked as attached but the originating module information hasn't been setup yet. It's unfortunate that we need to add a hash table entry in order to make it through duplicate_decls, at which point it becomes dead. Ah, well. I suppose with tsubst_friend_class it works though because we can't ever take the pushdecl branch if an existing type exists that we would call duplicate_decls on. 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 when the key is always a decl. Ah thanks, didn't know about decl_tree_map. I feel that I prefer using DECL_UIDs explicitly here though; it's also consistent with the existing usage in entity_map_t, and it looks like decl_tree_map is still perhaps vulnerable to the original issue here (since DECL_UID is only used for hashing and not for equality, it looks like?). Though that said, 'decl_constraints' in constraints.cc seems to be using it fine (well, with a GTY marking) by using 'remove_constraints' within duplicate_decls to clear this
[PATCH v3] c++/modules: Fix dangling pointer with imported_temploid_friends
On Thu, May 02, 2024 at 02:05:38PM -0400, Jason Merrill wrote: > 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 > > > > > --- > > > > > 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 *imported_temploid_friends; > > > > > +static GTY(()) hash_map *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, and then we tsubst_friend_function 'foo' from > > > > DEF, > > > > 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? > Doing that for tsubst_friend_class seems to work OK with my current test cases, but for tsubst_friend_function doing so causes ICEs in 'module_may_redeclare' within duplicate_decls because the function is already marked as attached but the originating module information hasn't been setup yet. I suppose with tsubst_friend_class it works though because we can't ever take the pushdecl branch if an existing type exists that we would call duplicate_decls on. > > > > 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 breaka
