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From: Martin Sebor <msebor@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-6712] Handle failure to determine pointer provenance conservatively [PR104069]. Date: Wed, 19 Jan 2022 01:04:19 +0000 (GMT) [thread overview] Message-ID: <20220119010419.C865F385780D@sourceware.org> (raw) https://gcc.gnu.org/g:2f714642e574c64e1c0e093cad3de6f8accb6ec7 commit r12-6712-g2f714642e574c64e1c0e093cad3de6f8accb6ec7 Author: Martin Sebor <msebor@redhat.com> Date: Tue Jan 18 17:52:01 2022 -0700 Handle failure to determine pointer provenance conservatively [PR104069]. Partly resolves: PR middle-end/104069 - -Werror=use-after-free false positive on elfutils-0.186 gcc/ChangeLog: PR middle-end/104069 * gimple-ssa-warn-access.cc (pointers_related_p): Return false for an unknown result as documented. gcc/testsuite/ChangeLog: PR middle-end/104069 * gcc.dg/Wuse-after-free.c: New test. Diff: --- gcc/gimple-ssa-warn-access.cc | 4 +++- gcc/testsuite/gcc.dg/Wuse-after-free.c | 41 ++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+), 1 deletion(-) diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc index f639807a78a..f9508a1d211 100644 --- a/gcc/gimple-ssa-warn-access.cc +++ b/gcc/gimple-ssa-warn-access.cc @@ -4082,7 +4082,9 @@ pointers_related_p (gimple *stmt, tree p, tree q, pointer_query &qry) access_ref pref, qref; if (!qry.get_ref (p, stmt, &pref, 0) || !qry.get_ref (q, stmt, &qref, 0)) - return true; + /* GET_REF() only rarely fails. When it does, it's likely because + it involves a self-referential PHI. Return a conservative result. */ + return false; return pref.ref == qref.ref; } diff --git a/gcc/testsuite/gcc.dg/Wuse-after-free.c b/gcc/testsuite/gcc.dg/Wuse-after-free.c new file mode 100644 index 00000000000..9862de5c0a9 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wuse-after-free.c @@ -0,0 +1,41 @@ +/* PR middle-end/104069 - -Werror=use-after-free false positive on + elfutils-0.186 + { dg-do compile } + { dg-options "-Wall" } */ + +typedef __SIZE_TYPE__ size_t; + +extern void* realloc (void *, size_t); + +void* __libdw_unzstd (size_t todo) +{ + void *sb = 0; + + for ( ; ; ) + { + // Ran only once. + if (!sb) + { + char *b = realloc (sb, todo); + if (!b) + break; + + sb = b; + } + + todo -= 1; + if (todo == 0) + break; + } + + // Shrink buffer: leave only one byte for simplicity. + char *b = realloc (sb, 1); + if (b) + sb = b; + else + { + // Realloc failed mysteriously, leave 'sb' untouched. + } + + return sb; // { dg-bogus "-Wuse-after-free" } +}
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