MaskRay added a comment. In D92633#2433999 <https://reviews.llvm.org/D92633#2433999>, @tmsriram wrote:
> In D92633#2433979 <https://reviews.llvm.org/D92633#2433979>, @MaskRay wrote: > >> In D92633#2433108 <https://reviews.llvm.org/D92633#2433108>, @tmsriram wrote: >> >>> You said : "The name -mpie-copy-relocations is misleading [1] and does not >>> capture the idea that this option can actually apply to all of >>> -fno-pic,-fpie, ..." >>> >>> Could you please clarify why this option needs to apply to -fno-pic? Here >>> is what I tried with trunk clang: >> >> If the user wants to guarantee no copy relocations in -fno-pic code, they >> can theoretically apply -fno-direct-access-external-data to use a GOT >> indirection. >> This is not implemented, though. >> >>> extern int var; >>> int get() { return var; } >>> >>> $ clang -S foo.c -o - >>> .... >>> movl var, %eax >>> popq %rbp >>> ... >>> >>> With -fno-pic, this will never need to use -mpie-copy-relocations at all, >>> so this case is not relevant right? Did I miss anything? >> >> -fno-pic code can only be used with -no-pie links (position-dependent >> executables) If var is not defined in the linked executable, it will have a >> copy relocation. > > Thanks for explaining. I know that by default (i.e. no-pic and no-pie), copy > relocations will be used for external data accesses. So, you are saying that > you are adding a mechanism to disable copy relocations for the no-pic/no-pie > case too. Is there a need for this, purely a question. I know that copy > relocations are frowned upon so maybe there was a feature request. If so, > citing that would make it more clear. Thanks. I don't know of a feature request. > Is there a need for this, purely a question. A weak need: more to make the behavior more align with the option name and perhaps align with potential GCC behavior (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98112). It can also be argued that this can be used to remove a special case for ppc64 ELFv2, which essentially defaults to -fno-direct-access-external-data for -fno-pic (they prefer to not have copy relocations) Supporting -fno-direct-access-external-data for -fno-pic is not difficult: a one/two line change to `TargetMachine::shouldAssumeDSOLocal` refining `if (!(GV && GV->isThreadLocal()) && RM == Reloc::Static)`. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D92633/new/ https://reviews.llvm.org/D92633 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
