On Tue, 9 Sep 2025, H.J. Lu wrote:
> On Tue, Sep 9, 2025 at 9:04 AM Alexander Monakov <amona...@ispras.ru> wrote: > > > > > > On Tue, 9 Sep 2025, H.J. Lu wrote: > > > > > > > to restore assert if not compiling for shared library. When compiling > > > > > for shared library, the recomputed model may be weaker. > > > > > > > > I don't understand why (for shared libraries), can you explain? > > > > > > Another shared library or executable may override any global > > > symbols with the default visibility in a shared library. > > > > I know that symbols with default visibility can be interposed, but that > > doesn't > > answer the question. Do you have a testcase that demonstrates the issue? > > TLS tests were submitted at > > https://patchwork.sourceware.org/project/gcc/patch/20250908221002.3223418-1-hjl.to...@gmail.com/ > > The key point is that compiler doesn't know if PIC code will be in > shared library or executable. But this doesn't imply that recomputed model would be weaker. As I understand, the actual issue is that decl_default_tls_model does not iterate the attribute list, and so can return a weaker model than what the front-end assigned based on the attribute. But this doesn't seem to have any relation to -fpic and shared libraries: you'll be in the same situation with extern TLS: __attribute__((tls_model("local-exec"))) extern __thread int tls_undef; where decl_default_tls_model returns initial-exec instead. Is this situation covered by existing tests? I expect your gcc_checking_assert (flag_shlib || new_model >= model); to fail on this. > > > x/1 (x) > > > Type: variable definition analyzed > > > Visibility: externally_visible semantic_interposition public common > > > References: > > > Referring: f/3 (addr) > > > Availability: overwritable > > > Varpool flags: tls-local-exec > > > > Thanks. Unrelated to this particular patch, but this is questionable: we > > have > > local-exec for an interposable (Availability: overwritable) symbol. Perhaps > > Definition in executable isn't interposable. But it's not a strong definition, it's common symbol. Anyway, just take attribute-common instead of attribute-weak: weak symbols are interposable. Alexander
