On 08/22/18 09:26, Richard Biener wrote:
> On Wed, 22 Aug 2018, Bernd Edlinger wrote:
>
>> On 08/21/18 10:59, Richard Biener wrote:
>>> On Tue, 21 Aug 2018, Bernd Edlinger wrote:
>>>
>>>> gcc -S -O2 -Wall -Wformat-overflow -ftrack-macro-expansion=0 -fshort-wchar
>>>> builtin-sprintf-warn-20.c
>>>> builtin-sprintf-warn-20.c: In function 'test':
>>>> builtin-sprintf-warn-20.c:19:39: warning: hex escape sequence out of range
>>>> 19 | ? (char*)L"\x4142\x4344" : (char*)L"\x41424344\x45464748";
>>>> | ^~~~~~~~~~~~~~~~~~~~~~~
>>>>
>>>> Hmm, this test might create some noise on short-wchar targets.
>>>>
>>>> I would prefer a warning here, about the wrong type of the parameter.
>>>> The buffer overflow is only a secondary thing.
>>>>
>>>> For constant objects like those, the GIMPLE type is still guaranteed to be
>>>> reliable,
>>>> right?
>>>
>>> TREE_TYPE of tcc_declaration and tcc_constant trees should more-or-less
>>> (minus qualifications not affecting semantics) be those set by
>>> frontends.
>>>
>>
>> and in this case:
>>
>> const union
>> { struct {
>> wchar_t x[4];
>> };
>> struct {
>> char z[8];
>> };
>> } u = {{L"123"}};
>>
>> int test()
>> {
>> return __builtin_strlen(u.z);
>> }
>>
>>
>> string_constant works out the initializer for u.x
>> which has a different type than u.z
>
> Yes. That's because it uses ctor-for-folding and friends. It's
> a question of the desired semantics of string_constant whether
> it should better return NULL_TREE in this case or whether the
> caller has to deal with type mismatches.
>
Yes, absolutely.
c_getstr needs to bail out if the string is not zero-terminated
within the limits given by the decl, or the string_cst-type or whatever
may help.
Furthermore I also consider it possible that the byteoffset
is not a multiple of eltsize. So fail in that case as well.
I am currently boot-strapping a patch for this (pr87053):
$ cat u.c
const union
{ struct {
char x[4];
char y[4];
};
struct {
char z[8];
};
} u = {{"1234", "567"}};
int test()
{
return __builtin_strlen(u.z);
}
gets folded to 4.
... but unfortunately it will depend on my pr86714 fix which fixes
the mem_size parameter returned from string_constant.
Frankly, in the moment I feel like I fell in a deep deep hole. :-O
Bernd.
