Re: [PATCH 5/5] extend -Warray-bounds to detect out-of-bounds accesses to array parameters

[Jeff Law <law@redhat.com>]

On Tue, 2020-07-28 at 19:24 -0600, Martin Sebor via Gcc-patches wrote:
> Patch 5 adds support for -Warray-bounds to detect out of bounds accesses
> in functions that take array/VLA arguments.  The changes also enable
> the warning for dynamically allocated memory and with it the detection
> of accesses that are only partially out of bounds (e.g., accessing
> a four byte int in the last two bytes of a buffer).  In hindsight this
> seems independent of the attribute access enhancement so I suppose it
> could have been split up into a separate change but I doubt it would
> reduce the size of the diff by more than 30 lines.

> [5/5] - Extend -Warray-bounds to detect out-of-bounds accesses to array parameters.
> 
> gcc/ChangeLog:
> 
> 	PR middle-end/82608
> 	PR middle-end/94195
> 	PR c/50584
> 	PR middle-end/84051
> 	* gimple-array-bounds.cc (get_base_decl): New function.
> 	(get_ref_size): New function.
> 	(trailing_array): New function.
> 	(array_bounds_checker::check_array_ref): Call them.  Handle arrays
> 	declared in function parameters.
> 	(array_bounds_checker::check_mem_ref):  Same.  Handle references to
> 	dynamically allocated arrays.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR middle-end/82608
> 	PR middle-end/94195
> 	PR c/50584
> 	PR middle-end/84051
> 	* gcc.dg/Warray-bounds-63.c: New test.
> 	* gcc.dg/Warray-bounds-64.c: New test.
> 	* gcc.dg/Warray-bounds-65.c: New test.
> 	* gcc.dg/Warray-bounds-66.c: New test.
> 
> diff --git a/gcc/gimple-array-bounds.cc b/gcc/gimple-array-bounds.cc
> index c2dd6663c3a..b93ef7a7b74 100644
> --- a/gcc/gimple-array-bounds.cc
> +++ b/gcc/gimple-array-bounds.cc
> @@ -36,6 +36,8 @@ along with GCC; see the file COPYING3.  If not see
>  #include "vr-values.h"
>  #include "domwalk.h"
>  #include "tree-cfg.h"
> +#include "attribs.h"
> +#include "builtins.h"
>  
>  // This purposely returns a value_range, not a value_range_equiv, to
>  // break the dependency on equivalences for this pass.
> @@ -46,19 +48,137 @@ array_bounds_checker::get_value_range (const_tree op)
>    return ranges->get_value_range (op);
>  }
>  
> +/* Try to determine the DECL that REF refers to.  Return the DECL or
> +   the expression closest to it.  Used in informational notes pointing
> +   to referenced objects or function parameters.  */
> +
> +static tree
> +get_base_decl (tree ref)
[ ... ]

> +
> +/* Return the constant byte size of the object or type referenced by
> +   the MEM_REF ARG.  On success, set *PREF to the DECL or expression
> +   ARG refers to.  Otherwise return null.  */
> +
> +static tree
> +get_ref_size (tree arg, tree *pref)
[ ... ]
I'm surprised we don't already have routines to do this.  
get_ref_base_and_extent perhaps?

Otherwise it seems reasonable to me.  
Jeff


>