* [PATCH] c++: Fix tinst_level::to_list [PR112968]
@ 2023-12-13 9:49 Jakub Jelinek
2023-12-13 17:23 ` Jason Merrill
0 siblings, 1 reply; 2+ messages in thread
From: Jakub Jelinek @ 2023-12-13 9:49 UTC (permalink / raw)
To: Jason Merrill; +Cc: gcc-patches
Hi!
With valgrind checking, there are various errors reported on some C++26
libstdc++ tests, like:
==2009913== Conditional jump or move depends on uninitialised value(s)
==2009913== at 0x914C59: gt_ggc_mx_lang_tree_node(void*) (gt-cp-tree.h:107)
==2009913== by 0x8AB7A5: gt_ggc_mx_tinst_level(void*) (gt-cp-pt.h:32)
==2009913== by 0xB89B25: ggc_mark_root_tab(ggc_root_tab const*) (ggc-common.cc:75)
==2009913== by 0xB89DF4: ggc_mark_roots() (ggc-common.cc:104)
==2009913== by 0x9D6311: ggc_collect(ggc_collect) (ggc-page.cc:2227)
==2009913== by 0xDB70F6: execute_one_pass(opt_pass*) (passes.cc:2738)
==2009913== by 0xDB721F: execute_pass_list_1(opt_pass*) (passes.cc:2755)
==2009913== by 0xDB7258: execute_pass_list(function*, opt_pass*) (passes.cc:2766)
==2009913== by 0xA55525: cgraph_node::analyze() (cgraphunit.cc:695)
==2009913== by 0xA57CC7: analyze_functions(bool) (cgraphunit.cc:1248)
==2009913== by 0xA5890D: symbol_table::finalize_compilation_unit() (cgraphunit.cc:2555)
==2009913== by 0xEB02A1: compile_file() (toplev.cc:473)
I think the problem is in the tinst_level::to_list optimization from 2018.
That function returns a TREE_LIST with TREE_PURPOSE/TREE_VALUE filled in.
Either it freshly allocates using build_tree_list (NULL, NULL); + stores
TREE_PURPOSE/TREE_VALUE, that case is fine (the whole tree_list object
is zeros, except for TREE_CODE set to TREE_LIST and TREE_PURPOSE/TREE_VALUE
modified later; the above also means in particular TREE_TYPE of it is NULL
and TREE_CHAIN is NULL and both are accessible/initialized even in valgrind
annotations.
Or it grabs a TREE_LIST node from a freelist.
If defined(ENABLE_GC_CHECKING), the object is still all zeros except
for TREE_CODE/TREE_PURPOSE/TREE_VALUE like in the fresh allocation case
(but unlike the build_tree_list case in the valgrind annotations
TREE_TYPE and TREE_CHAIN are marked as uninitialized).
If !defined(ENABLE_GC_CHECKING), I believe the actual memory content
is that everything but TREE_CODE/TREE_PURPOSE/TREE_VALUE/TREE_CHAIN is
zeros and TREE_CHAIN is something random (whatever next entry is in the
freelist, nothing overwrote it) and from valgrind POV again,
TREE_TYPE and TREE_CHAIN are marked as uninitialized.
When using the other freelist instantiations (pending_template and
tinst_level) I believe everything is correct, from valgrind POV it marks
the whole pending_template or tinst_level as uninitialized, but the
caller initializes it all).
One way to fix this would be let tinst_level::to_list not store just
TREE_PURPOSE (ret) = tldcl;
TREE_VALUE (ret) = targs;
but also
TREE_TYPE (ret) = NULL_TREE;
TREE_CHAIN (ret) = NULL_TREE;
Though, that seems like wasted effort in the build_tree_list case to me.
So, the following patch instead does that TREE_CHAIN = NULL_TREE store only
in the case where it isn't already done and marks both TREE_CHAIN and
TREE_TYPE as initialized (the latter is at that spot, the former is because
we never really touch TREE_TYPE of a TREE_LIST anywhere and so the NULL
gets stored into the freelist and restored from there (except for
ENABLE_GC_CHECKING where it is poisoned and then cleared again).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2023-12-13 Jakub Jelinek <jakub@redhat.com>
PR c++/112968
* pt.cc (freelist<tree_node>::reinit): Make whole obj->common
defined for valgrind annotations rather than just obj->base,
and do it even for ENABLE_GC_CHECKING. If not ENABLE_GC_CHECKING,
clear TREE_CHAIN (obj).
--- gcc/cp/pt.cc.jj 2023-12-11 23:52:03.592513063 +0100
+++ gcc/cp/pt.cc 2023-12-12 16:40:09.259903877 +0100
@@ -9525,7 +9525,7 @@ template <>
inline void
freelist<tree_node>::reinit (tree obj ATTRIBUTE_UNUSED)
{
- tree_base *b ATTRIBUTE_UNUSED = &obj->base;
+ tree_common *c ATTRIBUTE_UNUSED = &obj->common;
#ifdef ENABLE_GC_CHECKING
gcc_checking_assert (TREE_CODE (obj) == TREE_LIST);
@@ -9540,8 +9540,9 @@ freelist<tree_node>::reinit (tree obj AT
#ifdef ENABLE_GC_CHECKING
TREE_SET_CODE (obj, TREE_LIST);
#else
- VALGRIND_DISCARD (VALGRIND_MAKE_MEM_DEFINED (b, sizeof (*b)));
+ TREE_CHAIN (obj) = NULL_TREE;
#endif
+ VALGRIND_DISCARD (VALGRIND_MAKE_MEM_DEFINED (c, sizeof (*c)));
}
/* Point to the first object in the TREE_LIST freelist. */
Jakub
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] c++: Fix tinst_level::to_list [PR112968]
2023-12-13 9:49 [PATCH] c++: Fix tinst_level::to_list [PR112968] Jakub Jelinek
@ 2023-12-13 17:23 ` Jason Merrill
0 siblings, 0 replies; 2+ messages in thread
From: Jason Merrill @ 2023-12-13 17:23 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: gcc-patches
On 12/13/23 04:49, Jakub Jelinek wrote:
> Hi!
>
> With valgrind checking, there are various errors reported on some C++26
> libstdc++ tests, like:
> ==2009913== Conditional jump or move depends on uninitialised value(s)
> ==2009913== at 0x914C59: gt_ggc_mx_lang_tree_node(void*) (gt-cp-tree.h:107)
> ==2009913== by 0x8AB7A5: gt_ggc_mx_tinst_level(void*) (gt-cp-pt.h:32)
> ==2009913== by 0xB89B25: ggc_mark_root_tab(ggc_root_tab const*) (ggc-common.cc:75)
> ==2009913== by 0xB89DF4: ggc_mark_roots() (ggc-common.cc:104)
> ==2009913== by 0x9D6311: ggc_collect(ggc_collect) (ggc-page.cc:2227)
> ==2009913== by 0xDB70F6: execute_one_pass(opt_pass*) (passes.cc:2738)
> ==2009913== by 0xDB721F: execute_pass_list_1(opt_pass*) (passes.cc:2755)
> ==2009913== by 0xDB7258: execute_pass_list(function*, opt_pass*) (passes.cc:2766)
> ==2009913== by 0xA55525: cgraph_node::analyze() (cgraphunit.cc:695)
> ==2009913== by 0xA57CC7: analyze_functions(bool) (cgraphunit.cc:1248)
> ==2009913== by 0xA5890D: symbol_table::finalize_compilation_unit() (cgraphunit.cc:2555)
> ==2009913== by 0xEB02A1: compile_file() (toplev.cc:473)
>
> I think the problem is in the tinst_level::to_list optimization from 2018.
> That function returns a TREE_LIST with TREE_PURPOSE/TREE_VALUE filled in.
> Either it freshly allocates using build_tree_list (NULL, NULL); + stores
> TREE_PURPOSE/TREE_VALUE, that case is fine (the whole tree_list object
> is zeros, except for TREE_CODE set to TREE_LIST and TREE_PURPOSE/TREE_VALUE
> modified later; the above also means in particular TREE_TYPE of it is NULL
> and TREE_CHAIN is NULL and both are accessible/initialized even in valgrind
> annotations.
> Or it grabs a TREE_LIST node from a freelist.
> If defined(ENABLE_GC_CHECKING), the object is still all zeros except
> for TREE_CODE/TREE_PURPOSE/TREE_VALUE like in the fresh allocation case
> (but unlike the build_tree_list case in the valgrind annotations
> TREE_TYPE and TREE_CHAIN are marked as uninitialized).
> If !defined(ENABLE_GC_CHECKING), I believe the actual memory content
> is that everything but TREE_CODE/TREE_PURPOSE/TREE_VALUE/TREE_CHAIN is
> zeros and TREE_CHAIN is something random (whatever next entry is in the
> freelist, nothing overwrote it) and from valgrind POV again,
> TREE_TYPE and TREE_CHAIN are marked as uninitialized.
>
> When using the other freelist instantiations (pending_template and
> tinst_level) I believe everything is correct, from valgrind POV it marks
> the whole pending_template or tinst_level as uninitialized, but the
> caller initializes it all).
>
> One way to fix this would be let tinst_level::to_list not store just
> TREE_PURPOSE (ret) = tldcl;
> TREE_VALUE (ret) = targs;
> but also
> TREE_TYPE (ret) = NULL_TREE;
> TREE_CHAIN (ret) = NULL_TREE;
> Though, that seems like wasted effort in the build_tree_list case to me.
>
> So, the following patch instead does that TREE_CHAIN = NULL_TREE store only
> in the case where it isn't already done and marks both TREE_CHAIN and
> TREE_TYPE as initialized (the latter is at that spot, the former is because
> we never really touch TREE_TYPE of a TREE_LIST anywhere and so the NULL
> gets stored into the freelist and restored from there (except for
> ENABLE_GC_CHECKING where it is poisoned and then cleared again).
We sometimes do put things in the TREE_TYPE of a TREE_LIST, so I would
be more comfortable setting it here as well. OK with that change.
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2023-12-13 Jakub Jelinek <jakub@redhat.com>
>
> PR c++/112968
> * pt.cc (freelist<tree_node>::reinit): Make whole obj->common
> defined for valgrind annotations rather than just obj->base,
> and do it even for ENABLE_GC_CHECKING. If not ENABLE_GC_CHECKING,
> clear TREE_CHAIN (obj).
>
> --- gcc/cp/pt.cc.jj 2023-12-11 23:52:03.592513063 +0100
> +++ gcc/cp/pt.cc 2023-12-12 16:40:09.259903877 +0100
> @@ -9525,7 +9525,7 @@ template <>
> inline void
> freelist<tree_node>::reinit (tree obj ATTRIBUTE_UNUSED)
> {
> - tree_base *b ATTRIBUTE_UNUSED = &obj->base;
> + tree_common *c ATTRIBUTE_UNUSED = &obj->common;
>
> #ifdef ENABLE_GC_CHECKING
> gcc_checking_assert (TREE_CODE (obj) == TREE_LIST);
> @@ -9540,8 +9540,9 @@ freelist<tree_node>::reinit (tree obj AT
> #ifdef ENABLE_GC_CHECKING
> TREE_SET_CODE (obj, TREE_LIST);
> #else
> - VALGRIND_DISCARD (VALGRIND_MAKE_MEM_DEFINED (b, sizeof (*b)));
> + TREE_CHAIN (obj) = NULL_TREE;
> #endif
> + VALGRIND_DISCARD (VALGRIND_MAKE_MEM_DEFINED (c, sizeof (*c)));
> }
>
> /* Point to the first object in the TREE_LIST freelist. */
>
> Jakub
>
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