Re: [PATCH] track dynamic allocation in strlen (PR 91582)

[Martin Sebor <msebor@gmail.com>]

Ping: https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00812.html

On 11/11/19 6:27 PM, Martin Sebor wrote:
> The attached patch extends the strlen pass to detect out-of-bounds
> accesses to memory allocated by calls to other allocation functions
> besides calloc and malloc, as well as VLAs, and user-defined
> functions declared with attribute alloc_size.  There is some
> overlap with the _FORTIFY_SOURCE detection but thanks to
> the extensive use of ranges, this enhancement detects many more
> cases of overflow.
> 
> The solution primarily improves warnings but some of the changes
> also improve codegen in some cases as a side-effect.  I hope to
> take better advantage of the optimization opportunities the dynamic
> memory tracking opens up (and also better buffer overflow and array
> out-of-bounds detection) in GCC 11.
> 
> Although the strlen pass already tracks some dynamic memory calls
> (calloc and malloc) rather than extending the same infrastructure
> (strinfo::stmt) to others I took the approach of adding a separate
> data member for the other calls (strinfo::alloc) and tracking those
> independently.  I did this to keep the changes only minimally
> intrusive.  In the future (post GCC 10) it might be worth
> considering merging both.
> 
> Besides introducing the new member and making use of it, the rest
> of the changes were prompted by weaknesses exposed by test cases
> involving dynamically allocated objects.
> 
> The patch is intended to apply on top of the two related patches
> posted last week ([1] and [2]).  For all tests to pass also expects
> the fix for PR 92412 posted earlier today ([3]).
> 
> Martin
> 
> [1] https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00429.html
> [2] https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00652.html
> [3] https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00800.html