On Wed, Sep 16, 2020 at 9:53 AM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
> Consider a TU with file scoped "static const object utf8_sb_map". A
> routine within the TU will stuff &utf8_sb_map into an object, something
> like:
>
> fu (...)
>
> {
>
> if (cond)
>
> dfa->sb_char = utf8_sb_map;
>
> else
>
> dfa->sb_char = malloc (...);
>
> }
>
>
> There is another routine in the TU which looks like
>
> bar (...)
>
> {
>
> if (dfa->sb_char != utf8_sb_map)
>
> free (dfa->sb_char);
>
> }
>
>
> Now imagine that the TU is compiled (with LTO) into a static library,
> libgl.a and there's a DSO (libdso.so) which gets linked against libgl.a
> and references the first routine (fu). We get a copy of fu in the DSO
> along with a copy of utf8_sb_map.
>
>
> Then imagine there's a main executable that dynamicly links against
> libdso.so, then links statically against libgl.a. Assume the main
> executable does not directly reference fu(), but does call a routine in
> libdso.so which eventually calls fu(). Also assume the main executable
> directly calls bar(). Again, remember we're compiling with LTO, so we
> don't suck in the entire TU, just the routines/data we need.
>
>
> In this scenario, both libdso.so and the main executable are going to a
> copy of utf8_sb_map and they'll be at different addresses. So when the
> main executable calls into libdso.so which in turn calls libdso's copy
> of fu() which stuffs the address of utf8_sb_map from the DSO into
> dfa->sb_char. Later the main executable calls bar() that's in the main
> executable. It does the comparison to see if dfa->sb_char is equal to
> utf8_sb_map -- but it's using the main executable's copy of utf8_sb_map
> and naturally free() blows us because it was passed a static object, not
> a malloc'd object.
>
>
> ISTM this is a lot like the problem we have where we inline functions
> with static data. To fix those we use STB_GNU_UNIQUE. But I don't see
> any code in the C front-end which would utilize STB_GNU_UNIQUE. It's
> support seems limited to C++.
>
>
> How is this supposed to work for C?
>
>
> Jeff
>
>
Can you group utf8_sb_map, fu and bar together so that they are defined
together?
--
H.J.
