[Bug c/57120] New: Plain C link with libgcc_s_sjlj-1.dll which not needed

[dongsheng.song at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57120

             Bug #: 57120
           Summary: Plain C link with libgcc_s_sjlj-1.dll which not needed
    Classification: Unclassified
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: dongsheng.s...@gmail.com


Here is example:

$ cat t-w32.c
long long do_div(long long a, long long b)
{
  return a/b;
}

i686-w64-mingw32-gcc -shared -o t-w32.dll t-w32.c
i686-w64-mingw32-objdump -x t-w32.dll  | grep "DLL Name"

gcc 4.8:
        DLL Name: libgcc_s_sjlj-1.dll
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll

gcc 4.7:
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll

Then I investigate why the gcc 4.8 output dll use libgcc_s_sjlj-1.dll,
I found t-w32.dll use the following symbols in libgcc_s_sjlj-1.dll:

i686-w64-mingw32-objdump -x t-w32.dll  | less

        DLL Name: libgcc_s_sjlj-1.dll
        vma:  Hint/Ord Member-Name Bound-To
        c200       41  __divdi3
        c20c      119  __udivdi3
        c218      121  __umoddi3

I think this is a regress, isn't it ?


I found in gcc/config/i386/mingw32.h:

/* Include in the mingw32 libraries with libgcc */
#ifdef ENABLE_SHARED_LIBGCC
#define SHARED_LIBGCC_SPEC " \
 %{static|static-libgcc:-lgcc -lgcc_eh} \
 %{!static: \
   %{!static-libgcc: \
     %{!shared: \
       %{!shared-libgcc:-lgcc -lgcc_eh} \
       %{shared-libgcc:-lgcc_s -lgcc} \
      } \
     %{shared:-lgcc_s -lgcc} \
    } \
  } "
#else
#define SHARED_LIBGCC_SPEC " -lgcc "
#endif

If I change '-lgcc_s -lgcc' to '-lgcc -lgcc_s', then gcc 4.8 will not use such
symbols like __divdi3 in libgcc_s_sjlj-1.dll, it back to gcc 4.7 behavior.

Because both lib/libgcc_s.a (libgcc_s_sjlj-1.dll）and
lib/gcc/i686-w64-mingw32/4.8.1/libgcc.a
export these symbols:

___divdi3
___moddi3
___moddi3
...

I think this change is hastily, should be rollback, or make
libgcc_s${LIBGCC_EH_EXTN}-1.dll
DO NOT export extra symbols which not owned their self.