Re: [PATCH v2] tree-object-size: Support strndup and strdup

[Jeff Law <jeffreyalaw@gmail.com>]

On 11/4/22 06:48, Siddhesh Poyarekar wrote:
> Use string length of input to strdup to determine the usable size of the
> resulting object.  Avoid doing the same for strndup since there's a
> chance that the input may be too large, resulting in an unnecessary
> overhead or worse, the input may not be NULL terminated, resulting in a
> crash where there would otherwise have been none.
>
> gcc/ChangeLog:
>
> 	* tree-object-size.cc (todo): New variable.
> 	(object_sizes_execute): Use it.
> 	(strdup_object_size): New function.
> 	(call_object_size): Use it.
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.dg/builtin-dynamic-object-size-0.c (test_strdup,
> 	test_strndup, test_strdup_min, test_strndup_min): New tests.
> 	(main): Call them.
> 	* gcc.dg/builtin-dynamic-object-size-1.c: Silence overread
> 	warnings.
> 	* gcc.dg/builtin-dynamic-object-size-2.c: Likewise.
> 	* gcc.dg/builtin-dynamic-object-size-3.c: Likewise.
> 	* gcc.dg/builtin-dynamic-object-size-4.c: Likewise.
> 	* gcc.dg/builtin-object-size-1.c: Silence overread warnings.
> 	Declare free, strdup and strndup.
> 	(test11): New test.
> 	(main): Call it.
> 	* gcc.dg/builtin-object-size-2.c: Silence overread warnings.
> 	Declare free, strdup and strndup.
> 	(test9): New test.
> 	(main): Call it.
> 	* gcc.dg/builtin-object-size-3.c: Silence overread warnings.
> 	Declare free, strdup and strndup.
> 	(test11): New test.
> 	(main): Call it.
> 	* gcc.dg/builtin-object-size-4.c: Silence overread warnings.
> 	Declare free, strdup and strndup.
> 	(test9): New test.
> 	(main): Call it.

I'm struggling to see how the SSA updating is correct.  Yes we need to 
update the virtuals due to the introduction of the call to strlen, 
particularly when SRC is not a string constant.  But do we need to do more?

Don't we end up gimplifying the 1 + strlenfn (src) expression? Can that 
possibly create new SSA_NAMEs?  Do those need to be put into SSA form?  
I feel like I'm missing something here...


jeff