>> > The change to have all STRING_CSTs NUL terminated (but that NUL >> > termination not necessarily inclided in STRING_LENGTH) is a good >> > one. >> > >> > I'm not sure how we can reliably verify NUL termination after the >> > fact though and build_string already makes sure to NUL terminate >> > STRING_CSTs. So if GO strings are not NUL terminated then >> > the STRING_CSTs still are. >> >> The advantage is that there are less variations how string literals look >> like in the middle end. We will have a simple way to determine if >> a string literal is NUL terminated or not. And checking that property >> in varasm.c is exactly the right thing to do. >> >> String literals always have an array_type which may be shorter >> than TREE_STRING_LENGTH, but that chops off only exactly >> one wide character nul. Otherwise if the array_type is equal or larger, >> we know for sure the value is nul terminated. In the middle-end >> we can easily determine if a string is not NUL terminated by: >> >> compare_tree_int (TYPE_SIZE_UNIT (TREE_TYPE (init)), >> TREE_STRING_LENGTH (init)) < 0 >> >> I did use that already in my patch for pr86711. > > Hmm. How does that tell you whether the string is NUL terminated? > TREE_STRING_LENGTH includes the NUL termination and if it is > a significant char then TYPE_SIZE_UNIT should as well.
I debugged that code a lot recently. static const char x[2] = "ab" gives a TREE_STRING_LENGTH of 3, the TREE_TYPE of that beast is an array type for char[2]. and TYPE_SIZE_UNIT = 2. An ordinary C string "ab" has TYPE_SIZE_UNIT(TREE_TYPE(x)) = 3. Of course with wide caracher strings the TREE_STING_LENGTH and TYPE_SIZE_UNIT of the ARRAY_TYPE are multiple of the used wide character type. So I would like to be able to assume that the STRING_CST objects are internally always generated properly by the front end. And that the ARRAY_TYPE of the string literal either has the same length than the TREE_STRING_LENGTH or if it is shorter, this is always exactly one (wide) character size less than TREE_STRING_LENGTH The idea is to use this property of string literals where needed, and check rigorously in varasm.c. Does that make sense? > > Isn't a proper test to look at TREE_STRING_POINTER[TREE_STRING_LENGTH - 1] > (for HOST_CHAR_BITS strings)? > There are also wide character strings, and all those test are broken everywhere for wide characters right now. Therefore checking the string constants at varasm.c revealed a lot of intersting things. I will post several patches in the afternoon. > Relying on the type here looks somewhat fragile to me. > > Abstracting a string_cst_nul_terminated_p () helper would be a good > idea I guess. Yes. indeed. > I realize using strlen(TREE_STRING_POINTER) doesn't work because > of embedded NULs. > >> Additionally not having oversize string constants produced >> by the front ends, where the extra characters are good for nothing, >> also helps to improve correctness. >>
