From 7ff33c609a64319583223d6d39a89e971f993ecf Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Thu, 14 Dec 2023 07:57:34 +0100 Subject: c++: Fix tinst_level::to_list [PR112968] 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 likewise for TREE_TYPE just to be sure) 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). 2023-12-14 Jakub Jelinek PR c++/112968 * pt.cc (freelist::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) and TREE_TYPE (obj). --- gcc/cp/pt.cc | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'gcc') diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index b6a450c..810d33c 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -9525,7 +9525,7 @@ template <> inline void freelist::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 +9540,10 @@ freelist::reinit (tree obj ATTRIBUTE_UNUSED) #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; + TREE_TYPE (obj) = NULL_TREE; #endif + VALGRIND_DISCARD (VALGRIND_MAKE_MEM_DEFINED (c, sizeof (*c))); } /* Point to the first object in the TREE_LIST freelist. */ -- cgit v1.1