[PATCH] D101873: [clang] Support clang -fpic -fno-semantic-interposition for AArch64

Tue Jun 8 00:21:21 PDT 2021

MaskRay added a comment.

In D101873#2804669 <https://reviews.llvm.org/D101873#2804669>, @lanza wrote:

> Hey Fangrui, is there any reason this couldn't extend to armv7?

@lanza Always happy when more folks are interested in such kind of stuff:)
This needs backend work. See D101872 <https://reviews.llvm.org/D101872>. I don't have bandwidth working on 32-bit arm :)

Now that we don't optimize variables, the value of -fno-semantic-interposition is small.
-fno-semantic-interposition can save a PLT entry (and associated `R_*_JUMP_SLOT` dynamic relocation) if a default visibility STB_GLOBAL function is only called in its defining TU, not by other TUs linked into the shared object.
Its benefit is subsumed by ld -Bsymbolic-non-weak-functions (seems that binutils isn't enthusiastic https://sourceware.org/pipermail/binutils/2021-May/116753.html)

I asked whether GCC could provide a configure option defaulting -fno-semantic-interposition https://gcc.gnu.org/PR100937 and I even sent a patch. 
Oops it was immediately closed as a wontfix.
It is so unfortunate that so few people pay attention on performance.
If I still want to try something, my angle has to be ***security hardening** :  https://gcc.gnu.org/pipermail/gcc-patches/2021-June/572103.html

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D101873/new/

https://reviews.llvm.org/D101873