[PATCH] implement -Wrestrict for sprintf (PR 83688)

[Martin Sebor]

Ping: https://gcc.gnu.org/ml/gcc-patches/2019-10/msg00570.html

On 10/8/19 5:51 PM, Martin Sebor wrote:
> Attached is a resubmission of the -Wrestrict implementation for
> the sprintf family of functions.  The original patch was posted
> in 2017 but never approved.  This revision makes only a few minor
> changes to the original code, mostly necessitated by rebasing on
> the top of trunk.
> 
> The description from the original posting still applies today:
> 
>  Â  The enhancement works by first determining the base object (or
>  Â  pointer) from the destination of the sprintf call, the constant
>  Â  offset into the object (and subobject for struct members), and
>    its size.  For each %s argument, it then computes the same data.
>  Â  If it determines that overlap between the two is possible it
>  Â  stores the data for the directive argument (including the size
>    of the argument) for later processing.  After the whole call and
>  Â  format string have been processed, the code then iterates over
>  Â  the stored directives and their arguments and compares the size
>  Â  and length of the argument against the function's overall output.
>  Â  If they overlap it issues a warning.
> 
> The solution is pretty simple.  The only details that might be
> worth calling out are the addition of a few utility functions some
> of which at first glance look like they could be replaced by calls
> to existing utilities:
> 
>  Â *Â  array_elt_at_offset
>  Â *Â  field_at_offset
>  Â *Â  get_origin_and_offset
>  Â *Â  alias_offset
> 
> Specifically, get_origin_and_offset looks like a dead ringer for
> get_addr_base_and_unit_offset, except since the former is only
> used for warnings it is less conservative.  It also works with
> SSA_NAMEs.  This is also the function I expect to need to make
> changes to (and fix bugs in).  The rest of the functions are
> general utilities that could perhaps be moved to tree.c at some
> point when there is a use for them elsewhere (I have some work
> in progress that might need at least one of them).
> 
> Another likely question worth addressing is why the sprintf
> overlap detection isn't handled in gimple-ssa-warn-restrict.c.
> There is an opportunity for code sharing between the two "passes"
> but it will require some fairly intrusive changes to the latter.
> Those feel out of scope for the initial solution.
> 
> Finally, because of new dependencies between existing classes in
> the file, some code had to be moved around within it a bit.  That
> contributed to the size of the patch making the changes seem more
> extensive than they really are.
> 
> Tested on x86_64-linux with Binutils/GDB and Glibc.
> 
> Martin
> 
> The original submission:
> https://gcc.gnu.org/ml/gcc-patches/2017-07/msg00036.html