[PATCH] D46326: ThinLTO+CFI: short-circuit direct calls to jump table entries

[Peter Collingbourne via Phabricator via llvm-commits]

pcc added a comment.

You don't need cross-DSO CFI to reproduce this, the issue has to do with regular ELF interposition.

Here is a standalone reproducer:

  $ cat main.c
  void baz();
  void foo() {
    puts("main");
  }
  
  int main() {
    direct();
    indirect();
  }
  $ cat dso.c
  void foo() {
    puts("dso");
  }
  typedef void (*fp)();
  
  fp bar() { return foo; }
  void indirect() {
    bar()();
  }
  void direct() {
    foo();
  }
  $ ~/src2/llvm-project4/ra/bin/clang -fsanitize=cfi-icall -shared -o dso.so dso.c -flto -fPIC
  $ ~/src2/llvm-project4/ra/bin/clang -fsanitize=cfi-icall  -o main main.c -flto dso.so
  $ LD_LIBRARY_PATH=. ./main
  dso
  main

If I rebuild dso.so without cfi-icall I see the correct result:

  $ ~/src2/llvm-project4/ra/bin/clang  -shared -o dso.so dso.c -flto -fPIC
  $ LD_LIBRARY_PATH=. ./main
  main
  main


Repository:
  rL LLVM

https://reviews.llvm.org/D46326