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[PATCH] Fix uninitialized variable with ubsan on ARM (PR sanitizer/66977)
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jakub Jelinek <jakub at redhat dot com>, Jason Merrill <jason at redhat dot com>
- Date: Tue, 28 Jul 2015 15:13:41 +0200
- Subject: [PATCH] Fix uninitialized variable with ubsan on ARM (PR sanitizer/66977)
- Authentication-results: sourceware.org; auth=none
This fixes a problem where on ARM ubsan can introduce an uninitialized variable.
It's ARM only since the ARM C++ ABI says that when creating a pointer to member
function, the LSB of ptr discriminates between the address of a non-virtual member
function and the offset in the class's virtual table of the address of a virtual
function. That means the compiler will create a RSHIFT_EXPR, and with ubsan this
RSHIFT_EXPR is instrumented, i.e. the expression involves SAVE_EXPRs.
But this expr is used more times and that is the crux of the problem:
get_member_function_from_ptrfunc returns a tree that contains the expr, and here
4927 fn = get_member_function_from_ptrfunc (&object_addr, fn,
4928 complain);
4929 vec_safe_insert (*args, 0, object_addr);
4930 }
it also saves the expr into OBJECT_ADDR which is then pushed to args.
Long story short: can't use unshare_expr here, because that doesn't copy
SAVE_EXPRs. I could use copy_tree_r, as outlined in the PR. But I think
we can just not instrument the RSHIFT_EXPR -- we know that this one can't
overflow anyway.
I have tried on a cross that the problem indeed goes away.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2015-07-28 Marek Polacek <polacek@redhat.com>
PR sanitizer/66977
* typeck.c (get_member_function_from_ptrfunc): Don't sanitize
RSHIFT_EXPR.
* g++.dg/ubsan/pr66977.C: New test.
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 2ed43be..8530be5 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -3288,6 +3288,7 @@ get_member_function_from_ptrfunc (tree *instance_ptrptr, tree function,
idx = build1 (NOP_EXPR, vtable_index_type, e3);
switch (TARGET_PTRMEMFUNC_VBIT_LOCATION)
{
+ int flag_sanitize_save;
case ptrmemfunc_vbit_in_pfn:
e1 = cp_build_binary_op (input_location,
BIT_AND_EXPR, idx, integer_one_node,
@@ -3303,9 +3304,15 @@ get_member_function_from_ptrfunc (tree *instance_ptrptr, tree function,
e1 = cp_build_binary_op (input_location,
BIT_AND_EXPR, delta, integer_one_node,
complain);
+ /* Don't instrument the RSHIFT_EXPR we're about to create because
+ we're going to use DELTA number of times, and that wouldn't play
+ well with SAVE_EXPRs therein. */
+ flag_sanitize_save = flag_sanitize;
+ flag_sanitize = 0;
delta = cp_build_binary_op (input_location,
RSHIFT_EXPR, delta, integer_one_node,
complain);
+ flag_sanitize = flag_sanitize_save;
if (delta == error_mark_node)
return error_mark_node;
break;
diff --git gcc/testsuite/g++.dg/ubsan/pr66977.C gcc/testsuite/g++.dg/ubsan/pr66977.C
index e69de29..3ab8d90 100644
--- gcc/testsuite/g++.dg/ubsan/pr66977.C
+++ gcc/testsuite/g++.dg/ubsan/pr66977.C
@@ -0,0 +1,27 @@
+// PR sanitizer/66977
+// { dg-do compile }
+// { dg-options "-fsanitize=shift -Wmaybe-uninitialized -O" }
+
+class Foo {
+
+private:
+
+ int a_;
+
+public:
+
+ Foo (int a) : a_(a) {};
+
+ inline int get_a () { return a_; };
+};
+
+int bar (int (Foo::*get)()) {
+ Foo *A = new Foo(1);
+ int result = (A->*get)();
+ delete (A);
+ return result;
+}
+
+int main () {
+ return bar (&Foo::get_a);
+}
Marek