Re: [PATCH] improve handling of aggregates in sprintf [PR 102238, 102919]

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/24/2021 5:43 PM, Martin Sebor via Gcc-patches wrote:
> The detection of overlapping sprintf calls has a limitation
> that leads to both false positives (PR 102919) and negatives
> (PR 102238) in corner cases involving members of aggregates.
> The false positives result from the overlap logic not using
> the size of the member used as an argument to %s to constrain
> the length of the directive output.  The false negatives are
> due to the logic failing to determine the identity of a member
> from the address or reference to the enclosing object and
> an offset.
>
> The attached patch improves the detection logic to handle both
> sets of cases.  In addition, it moves the utility functions used
> to implement the logic from the sprintf pass into pointer-query
> where they can be used for other purposes in the future (my
> work in progress).
>
> Tested on x86_64-linux and by building Glibc and verifying
> it doesn't cause any new warnings,
>
> Martin
>
> gcc-102238.diff
>
> PR tree-optimization/102238 - alias_offset in gimple-ssa-sprintf.c is broken
> PR tree-optimization/102919 - spurious -Wrestrict warning for sprintf into the same member array as argument plus offset
>
> gcc/ChangeLog:
>
> 	PR tree-optimization/102238
> 	PR tree-optimization/102919
> 	* gimple-ssa-sprintf.c (get_string_length): Ad an argument.
> 	(array_elt_at_offset): Move to pointer-query.
> 	(set_aggregate_size_and_offset): New function.
> 	(field_at_offset):  Move to pointer-query.
> 	(get_origin_and_offset): Rename...
> 	(get_origin_and_offset_r): this.  Add an argument.  Make aggregate
> 	handling more robust.
> 	(get_origin_and_offset): New.
> 	(alias_offset): Add an argument.
> 	(format_string): Use subobject size determined by get_origin_and_offset.
> 	* pointer-query.cc (field_at_offset): Move from gimple-ssa-sprintf.c.
> 	Improve/correct handling of aggregates.
> 	(array_elt_at_offset): Same.
> 	* pointer-query.h (field_at_offset): Declare.
> 	(array_elt_at_offset): Declare.
>
> gcc/testsuite/ChangeLog:
>
> 	PR tree-optimization/102238
> 	PR tree-optimization/102919
> 	* gcc.dg/tree-ssa/builtin-sprintf-warn-23.c: Remove warnings.
> 	* gcc.dg/Wrestrict-23.c: New test.
Given you know this code better than anyone.  OK.
jeff