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

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 2022-11-20 10:42, Jeff Law wrote:
> 
> 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...

We do all of that manually in gimplify_size_expressions, the only thing 
left to do is updating virtuals AFAICT.

Thanks,
Sid