Re: PING [PATCH] warn for strlen of arrays with missing nul (PR 86552, 86711, 86714) )

[Bernd Edlinger <bernd dot edlinger at hotmail dot de>]

On 08/02/18 15:26, Bernd Edlinger wrote:
>>
>>    /* If the length can be computed at compile-time, return it.  */
>> -  len = c_strlen (src, 0);
>> +  tree array;
>> +  tree len = c_strlen (src, 0, &array);
> 
> You know the c_strlen tries to compute wide character sizes,
> but strlen does not do that, strlen (L"abc") should give 1
> (or 0 on a BE machine)
> I wonder if that is correct.
> 
[snip]
>>
>>  static tree
>> -fold_builtin_strlen (location_t loc, tree type, tree arg)
>> +fold_builtin_strlen (location_t loc, tree fndecl, tree type, tree arg)
>>  {
>>    if (!validate_arg (arg, POINTER_TYPE))
>>      return NULL_TREE;
>>    else
>>      {
>> -      tree len = c_strlen (arg, 0);
>> -
>> +      tree arr = NULL_TREE;
>> +      tree len = c_strlen (arg, 0, &arr);
> 
> Is it possible to write a test case where strlen(L"test") reaches this point?
> what will c_strlen return then?
> 

Yes, of course it is:

$ cat y.c
int f(char *x)
{
   return __builtin_strlen(x);
}

int main ()
{
   return f((char*)&L"abcdef"[0]);
}
$ gcc -O3 -S y.c
$ cat y.s
main:
.LFB1:
	.cfi_startproc
	movl	$6, %eax
	ret
	.cfi_endproc

The reason is that c_strlen tries to fold wide chars at all.
I do not know when that was introduced, was that already before your last patches?
Is it possible to revert the last few patches cleanly?


Bernd.