[Bug ld/25940] New: ld.bfd, clang’s ubsan, shared libraries, and virtual tables do not work together

[dilyan.palauzov at aegee dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=25940

            Bug ID: 25940
           Summary: ld.bfd, clang’s ubsan, shared libraries, and virtual
                    tables do not work together
           Product: binutils
           Version: 2.35 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: dilyan.palauzov at aegee dot org
  Target Milestone: ---

I have ld.bfd 2.34.50.20200506, ld.gold 2.34.50.20200506, gcc/g++ 9.3.1
20200506, ld.lld 10.0.0, clang(++) 10.0.0, z.cpp:
  #include <stdio.h>
  #include <stdbool.h>
  #include <string>

  struct x {
    std::string x;
  };

  struct z: virtual x {
    z() {
      bool b = 99;
      printf("a %i\n", b);
    }
  };

  extern "C" {
    void y();
  }

  void y() {
    const x x1 = z();
  }

and a.c:
  void y();

  int main() {
    y();
  }

With --- CLANG ---

> clang++ -shared -fsanitize=address,undefined z.cpp -fpic -o libz.so
> nm -D libz.so|grep san
<                 U __asan_init
<                 U __asan_option_detect_stack_use_after_return
<                 U __asan_register_globals
<                 U __asan_report_load8
<                 U __asan_report_store8
<                 U __asan_stack_malloc_2
<                 U __asan_unregister_globals
<                 U __asan_version_mismatch_check_v8
<                 U __ubsan_handle_dynamic_type_cache_miss
<                 U __ubsan_handle_load_invalid_value
<                 U __ubsan_handle_type_mismatch_v1
<                 U __ubsan_vptr_type_cache
> clang -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=bfd
< /usr/local/bin/ld.bfd: ./libz.so: undefined reference to
`__ubsan_vptr_type_cache'
< /usr/local/bin/ld.bfd: ./libz.so: undefined reference to
`__ubsan_handle_dynamic_type_cache_miss'
<  clang-10: error: linker command failed with exit code 1 (use -v to see
invocation)

But if I remove the class conversions from z.cpp, then libz.so does not
contains __ubsan_vptr_type_cache as Undefined symbol, while it contains
__ubsan_handle_load_invalid_value, and then the linking clang+ld.bfd does work
> clang -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=bfd -lubsan
< (No error, no warning)  
> LD_LIBRARY_PATH=. ./b
< a 1
> clang -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=gold
< /usr/local/bin/ld.gold: warning: Cannot export local symbol
'__asan_extra_spill_area'
> LD_LIBRARY_PATH=. ./b
< ./b: symbol lookup error: ./libz.so: undefined symbol:
__ubsan_vptr_type_cache
> clang -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=gold -lubsan
< /usr/local/bin/ld.gold: warning: Cannot export local symbol
'__asan_extra_spill_area'
> LD_LIBRARY_PATH=. ./b
< a 1
> clang -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=lld
< (No error, no warning)
> LD_LIBRARY_PATH=. ./b
< ./b: symbol lookup error: ./libz.so: undefined symbol:
__ubsan_vptr_type_cache
> clang -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=lld -lubsan
< (No error, no warning)
> LD_LIBRARY_PATH=. ./b
< a 1

--- GCC ---
> g++ -shared -fsanitize=address,undefined z.cpp -fpic -o libz.so
> nm -D libz.so|grep san
<                 U __asan_handle_no_return
<                 U __asan_init
<                 U __asan_option_detect_stack_use_after_return
<                 U __asan_register_globals
<                 U __asan_report_load8
<                 U __asan_report_store8
<                 U __asan_stack_malloc_2
<                 U __asan_unregister_globals
<                 U __asan_version_mismatch_check_v8
<                 U __ubsan_handle_dynamic_type_cache_miss
<                 U __ubsan_handle_pointer_overflow
<                 U __ubsan_handle_type_mismatch_v1
<                 U __ubsan_vptr_type_cache
> gcc -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=bfd
< (No error, no warning)
> LD_LIBRARY_PATH=. ./b
< a 1
> gcc -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=gold
< (No error, no warning)
> LD_LIBRARY_PATH=. ./b
< a 1
> gcc -fsanitize=address,undefined -o b b.c -L. -lz -fuse-ld=lld
< (No error, no warning)
> LD_LIBRARY_PATH=. ./b
< a 1

• Why does clang+ld.bfd produce an error when using ubsan with class
conversions?
• Why do I have to add in clang+ld.bfd -lubsan to get rid of the warning?
• Why does clang+ld.bfd does not produce an error when ubsan does no class
conversions?
• Why does clang+ld.gold produce a warning?

Note that I have LLVMGold.so in /usr/local/lib, but not in
/usr/local/lib/bfd-plugins.  It is therefore not used by the linker (and this
LLVMGold.so is for LLVM 8, as I forgot te complice LLVM 10 with the linker
plugin).

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