[LLVMbugs] [Bug 21001] New: clang++ doesn't export operator delete with -flto

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21001

            Bug ID: 21001
           Summary: clang++ doesn't export operator delete with -flto
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: tavianator at tavianator.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

When using -flto, clang doesn't export a replacement operator delete, causing
shared libraries to call a different implementation than the main program. 
Example:

$ cat main.cpp
#include <cstdlib>
#include <new>
#include <iostream>

void* operator new(std::size_t size) {
  void* result = std::malloc(size);
  if (result == nullptr) {
    operator delete(result);
    throw std::bad_alloc();
  }
  return result;
}

void operator delete(void* ptr) noexcept {
  std::cout << "Deleting!" << std::endl;
  std::free(ptr);
}

void deleteIt(int* ptr);

int main() {
  deleteIt(new int);
  return 0;
}
$ cat shared.cpp
void deleteIt(int* ptr) {
  delete ptr;
}
$ clang++ -std=c++11 -g -O3 -flto -fuse-ld=gold -fPIC -shared shared.cpp -o
libshared.so
$ clang++ -std=c++11 -g -O3 -flto -fuse-ld=gold main.cpp -L. -lshared -o main
$ LD_LIBRARY_PATH=. ./main
$

(Note the missing "Deleting!" output.)  objdump shows that the symbol isn't
exported:

$ objdump -T main | c++filt | grep operator
0000000000400e40 g    DF .text  000000000000003a  Base        operator
new(unsigned long)
0000000000000000      DF *UND*  0000000000000000  Base        operator
delete(void*)

The bug happens with C++98 mode too (with appropriate code changes), but the
C++14 operator delete(void*, std::size_t) works.

A workaround is to add __attribute__((used)) to operator delete.  See
http://stackoverflow.com/q/25922895/502399.

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