On 01/03/2014 10:43 PM, Florian Weimer wrote:
Lastly, I wonder if gimple_call_return_slot_opt_p is really what you are
after, why does NRV matter here?
The C code we generate does not construct the returned value in place
(presumably because the partial write would be visible with threads,
longjmp etc.), unlike the C++ code.
That's why I'm interested in instrumenting NRV-able calls only. But
gimple_call_return_slot_opt_p doesn't actually give me that. The GIMPLE
from the C test case looks like this (before and after applying your
proposal):
I thought about this some more and I think it makes sense to add the
instrumentation each time the return slot is used, both for C and C++.
We don't if the called function is implemented in C or C++, so
language-specific instrumentation is not entirely accurate.
I'm attaching a second version of the patch, splitting out the decl and
bb analysis and using is_gimple_call. Bootstrapped and
regression-tested on x86_64-redhat-linux-gnu.
--
Florian Weimer / Red Hat Product Security Team
gcc/
2014-01-07 Florian Weimer <fwei...@redhat.com>
* cfgexpand.c (stack_protect_decl_p): New function, extracted from
expand_used_vars.
(stack_protect_return_slot_p): New function.
(expand_used_vars): Call stack_protect_decl_p and
stack_protect_return_slot_p for -fstack-protector-strong.
gcc/testsuite/
2014-01-07 Florian Weimer <fwei...@redhat.com>
* gcc.dg/fstack-protector-strong.c: Add coverage for return slots.
* g++.dg/fstack-protector-strong.C: Likewise.
Index: gcc/cfgexpand.c
===================================================================
--- gcc/cfgexpand.c (revision 206311)
+++ gcc/cfgexpand.c (working copy)
@@ -1599,6 +1599,47 @@
return 0;
}
+/* Check if the current function has local referenced variables that
+ have their addresses taken, contain an array, or are arrays. */
+
+static bool
+stack_protect_decl_p ()
+{
+ unsigned i;
+ tree var;
+
+ FOR_EACH_LOCAL_DECL (cfun, i, var)
+ if (!is_global_var (var))
+ {
+ tree var_type = TREE_TYPE (var);
+ if (TREE_CODE (var) == VAR_DECL
+ && (TREE_CODE (var_type) == ARRAY_TYPE
+ || TREE_ADDRESSABLE (var)
+ || (RECORD_OR_UNION_TYPE_P (var_type)
+ && record_or_union_type_has_array_p (var_type))))
+ return true;
+ }
+ return false;
+}
+
+/* Check if the current function has calls that use a return slot. */
+
+static bool
+stack_protect_return_slot_p ()
+{
+ basic_block bb;
+
+ FOR_ALL_BB_FN (bb, cfun)
+ for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
+ !gsi_end_p (gsi); gsi_next (&gsi))
+ {
+ gimple stmt = gsi_stmt (gsi);
+ if (is_gimple_call (stmt) && gimple_call_return_slot_opt_p (stmt))
+ return true;
+ }
+ return false;
+}
+
/* Expand all variables used in the function. */
static rtx
@@ -1669,22 +1710,8 @@
pointer_map_destroy (ssa_name_decls);
if (flag_stack_protect == SPCT_FLAG_STRONG)
- FOR_EACH_LOCAL_DECL (cfun, i, var)
- if (!is_global_var (var))
- {
- tree var_type = TREE_TYPE (var);
- /* Examine local referenced variables that have their addresses taken,
- contain an array, or are arrays. */
- if (TREE_CODE (var) == VAR_DECL
- && (TREE_CODE (var_type) == ARRAY_TYPE
- || TREE_ADDRESSABLE (var)
- || (RECORD_OR_UNION_TYPE_P (var_type)
- && record_or_union_type_has_array_p (var_type))))
- {
- gen_stack_protect_signal = true;
- break;
- }
- }
+ gen_stack_protect_signal
+ = stack_protect_decl_p () || stack_protect_return_slot_p ();
/* At this point all variables on the local_decls with TREE_USED
set are not associated with any block scope. Lay them out. */
Index: gcc/testsuite/g++.dg/fstack-protector-strong.C
===================================================================
--- gcc/testsuite/g++.dg/fstack-protector-strong.C (revision 206311)
+++ gcc/testsuite/g++.dg/fstack-protector-strong.C (working copy)
@@ -32,4 +32,39 @@
return global_func (a);
}
-/* { dg-final { scan-assembler-times "stack_chk_fail" 2 } } */
+/* Frame addressed exposed through return slot. */
+
+struct B
+{
+ /* Discourage passing this struct in registers. */
+ int a1, a2, a3, a4, a5, a6, a7, a8, a9, a10;
+};
+
+B global_func ();
+void noop ();
+
+int foo3 ()
+{
+ return global_func ().a1;
+}
+
+int foo4 ()
+{
+ try {
+ noop ();
+ return 0;
+ } catch (...) {
+ return global_func ().a1;
+ }
+}
+
+int foo5 ()
+{
+ try {
+ return global_func ().a1;
+ } catch (...) {
+ return 0;
+ }
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 5 } } */
Index: gcc/testsuite/gcc.dg/fstack-protector-strong.c
===================================================================
--- gcc/testsuite/gcc.dg/fstack-protector-strong.c (revision 206311)
+++ gcc/testsuite/gcc.dg/fstack-protector-strong.c (working copy)
@@ -131,4 +131,17 @@
return bb.three;
}
-/* { dg-final { scan-assembler-times "stack_chk_fail" 10 } } */
+struct B
+{
+ /* Discourage passing this struct in registers. */
+ int a1, a2, a3, a4, a5, a6, a7, a8, a9, a10;
+};
+
+struct B global3 (void);
+
+int foo11 ()
+{
+ return global3 ().a1;
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 11 } } */
