tree-optimization/105726 - adjust array bound heuristic
Commit Message
There's heuristic to detect ptr[1].a[...] out of bound accesses
reasoning that if ptr points to an array of aggregates a trailing
incomplete array has to have size zero. The following more
thoroughly constrains the cases this applies to avoid false
positive diagnostics.
Bootstrapped and tested on x86_64-unknown-linux-gnu.
OK?
Thanks,
Richard.
2022-05-25 Richard Biener <rguenther@suse.de>
PR tree-optimization/105726
* gimple-ssa-warn-restrict.cc (builtin_memref::set_base_and_offset):
Constrain array-of-flexarray case more.
* g++.dg/warn/Warray-bounds-27.C: New testcase.
---
gcc/gimple-ssa-warn-restrict.cc | 22 ++++++++++++--------
gcc/testsuite/g++.dg/warn/Warray-bounds-27.C | 16 ++++++++++++++
2 files changed, 29 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Warray-bounds-27.C
Comments
On 5/25/22 04:49, Richard Biener wrote:
> There's heuristic to detect ptr[1].a[...] out of bound accesses
> reasoning that if ptr points to an array of aggregates a trailing
> incomplete array has to have size zero. The following more
> thoroughly constrains the cases this applies to avoid false
> positive diagnostics.
The code in the area below does look like it's missing some logic
(like what you're adding). The whole -Wrestrict pass is messy and
could use some cleanup (sorry). The -Warray-bounds logic should
probably be removed (-Wstringop-overflow should now catch most of
the valid instances it issues, and if it doesn't(*) it should be
enhanced). The pass could even be moved into the access warning
pass and probably also simplified quite a bit.
For what it's worth, a simple C test case for the same bug is:
struct A
{
int i;
struct B { char a[1]; } b;
};
void f (char *d, struct A *p)
{
struct B *q = &p->b;
__builtin_strncpy (d, q->a, 1); // { dg-bogus "-Warray-bounds" }
}
Martin
[*] For example, no warning is issued for the following overread:
struct A a;
void g (char *d)
{
struct B *q = &a.b;
__builtin_strncpy (d, q->a, 123); // { dg-warning
"-Wstringop-overread" "pr???????" { xfail *-*-* } }
}
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> OK?
>
> Thanks,
> Richard.
>
> 2022-05-25 Richard Biener <rguenther@suse.de>
>
> PR tree-optimization/105726
> * gimple-ssa-warn-restrict.cc (builtin_memref::set_base_and_offset):
> Constrain array-of-flexarray case more.
>
> * g++.dg/warn/Warray-bounds-27.C: New testcase.
> ---
> gcc/gimple-ssa-warn-restrict.cc | 22 ++++++++++++--------
> gcc/testsuite/g++.dg/warn/Warray-bounds-27.C | 16 ++++++++++++++
> 2 files changed, 29 insertions(+), 9 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Warray-bounds-27.C
>
> diff --git a/gcc/gimple-ssa-warn-restrict.cc b/gcc/gimple-ssa-warn-restrict.cc
> index b678e806da3..734cdd7f5b4 100644
> --- a/gcc/gimple-ssa-warn-restrict.cc
> +++ b/gcc/gimple-ssa-warn-restrict.cc
> @@ -525,7 +525,6 @@ builtin_memref::set_base_and_offset (tree expr)
> {
> tree memrefoff = fold_convert (ptrdiff_type_node, TREE_OPERAND (base, 1));
> extend_offset_range (memrefoff);
> - base = TREE_OPERAND (base, 0);
>
> if (refoff != HOST_WIDE_INT_MIN
> && TREE_CODE (expr) == COMPONENT_REF)
> @@ -538,14 +537,19 @@ builtin_memref::set_base_and_offset (tree expr)
> REFOFF is set to s[1].b - (char*)s. */
> offset_int off = tree_to_shwi (memrefoff);
> refoff += off;
> - }
> -
> - if (!integer_zerop (memrefoff))
> - /* A non-zero offset into an array of struct with flexible array
> - members implies that the array is empty because there is no
> - way to initialize such a member when it belongs to an array.
> - This must be some sort of a bug. */
> - refsize = 0;
> +
> + if (!integer_zerop (memrefoff)
> + && !COMPLETE_TYPE_P (TREE_TYPE (expr))
> + && multiple_of_p (sizetype, memrefoff,
> + TYPE_SIZE_UNIT (TREE_TYPE (base)), true))
> + /* A non-zero offset into an array of struct with flexible array
> + members implies that the array is empty because there is no
> + way to initialize such a member when it belongs to an array.
> + This must be some sort of a bug. */
> + refsize = 0;
> + }
> +
> + base = TREE_OPERAND (base, 0);
> }
>
> if (TREE_CODE (ref) == COMPONENT_REF)
> diff --git a/gcc/testsuite/g++.dg/warn/Warray-bounds-27.C b/gcc/testsuite/g++.dg/warn/Warray-bounds-27.C
> new file mode 100644
> index 00000000000..06ce089c4b0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Warray-bounds-27.C
> @@ -0,0 +1,16 @@
> +// PR105726
> +// { dg-do compile }
> +// { dg-require-effective-target c++11 }
> +// { dg-options "-O2 -Warray-bounds" }
> +
> +#include <array>
> +#include <cstring>
> +
> +struct X {
> + char pad[4];
> + std::array<char, 1> mField;
> +};
> +
> +void encode(char* aBuffer, const X& aMessage) {
> + strncpy(aBuffer, aMessage.mField.data(), 1); // { dg-bogus "bounds" }
> +}
On 5/25/22 11:19, Martin Sebor wrote:
> On 5/25/22 04:49, Richard Biener wrote:
...
> [*] For example, no warning is issued for the following overread:
Scratch that, there is no overread with strncpy. When there is like
with memcpy, it is diagnosed as it should be.
>
> struct A a;
>
> void g (char *d)
> {
> struct B *q = &a.b;
> __builtin_strncpy (d, q->a, 123); // { dg-warning
> "-Wstringop-overread" "pr???????" { xfail *-*-* } }
> }
@@ -525,7 +525,6 @@ builtin_memref::set_base_and_offset (tree expr)
{
tree memrefoff = fold_convert (ptrdiff_type_node, TREE_OPERAND (base, 1));
extend_offset_range (memrefoff);
- base = TREE_OPERAND (base, 0);
if (refoff != HOST_WIDE_INT_MIN
&& TREE_CODE (expr) == COMPONENT_REF)
@@ -538,14 +537,19 @@ builtin_memref::set_base_and_offset (tree expr)
REFOFF is set to s[1].b - (char*)s. */
offset_int off = tree_to_shwi (memrefoff);
refoff += off;
- }
-
- if (!integer_zerop (memrefoff))
- /* A non-zero offset into an array of struct with flexible array
- members implies that the array is empty because there is no
- way to initialize such a member when it belongs to an array.
- This must be some sort of a bug. */
- refsize = 0;
+
+ if (!integer_zerop (memrefoff)
+ && !COMPLETE_TYPE_P (TREE_TYPE (expr))
+ && multiple_of_p (sizetype, memrefoff,
+ TYPE_SIZE_UNIT (TREE_TYPE (base)), true))
+ /* A non-zero offset into an array of struct with flexible array
+ members implies that the array is empty because there is no
+ way to initialize such a member when it belongs to an array.
+ This must be some sort of a bug. */
+ refsize = 0;
+ }
+
+ base = TREE_OPERAND (base, 0);
}
if (TREE_CODE (ref) == COMPONENT_REF)
new file mode 100644
@@ -0,0 +1,16 @@
+// PR105726
+// { dg-do compile }
+// { dg-require-effective-target c++11 }
+// { dg-options "-O2 -Warray-bounds" }
+
+#include <array>
+#include <cstring>
+
+struct X {
+ char pad[4];
+ std::array<char, 1> mField;
+};
+
+void encode(char* aBuffer, const X& aMessage) {
+ strncpy(aBuffer, aMessage.mField.data(), 1); // { dg-bogus "bounds" }
+}