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* [gcc r12-6712] Handle failure to determine pointer provenance conservatively [PR104069].
@ 2022-01-19 1:04 Martin Sebor
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From: Martin Sebor @ 2022-01-19 1:04 UTC (permalink / raw)
To: gcc-cvs
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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