Re: Define __start/__stop symbols when there is only a dynamic def

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Jan 29, 2018 at 7:26 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Mon, 29 Jan 2018, H.J. Lu wrote:
>
>> Yes, it looks very odd.  I thought the issue was with the  __start/__stop
>> symbols in the shared object, not with executable.  Why is -E needed?
>> I don't want to second guess.  Michael, can you provide a testcase to
>> show your use case?
>
> It's exactly as I described in the thread linked by Alan.  But sure,
> here's some code:
>
> % cat lib.c
> extern int __start___verbose[];
> extern int __stop___verbose[];
> extern int foo2(void);
> int foo (void)
> {
>   static int my_var __attribute__((section("__verbose"))) = 5;
>   if (__start___verbose == __stop___verbose  // ref_regular
>       || __start___verbose[0] != 5)
>     return -1;
>   else
>     return 0;
> }
> % cat app.c
> #include <stdlib.h>
> #include <stdio.h>
> extern int foo (void);
> extern int __start___verbose[];
> extern int __stop___verbose[];
> int bar (void)
> {
>   static int my_var __attribute__((section("__verbose"))) = 6;
>   // no ref_regular!
>   return 0;
> }
>
> int main()
> {
>   if (bar () != 0)
>     {
>       printf("main: wrong __start___verbose\n");
>       exit(2);
>     }
>   return 0;
> }
> % cc -g   -c -o app.o app.c
> % cc -g -fPIC   -c -o lib.o lib.c
> % cc -B./ -shared -o liborphan.so lib.o -Wl,-R,.
> % cc -B./ -o app app.o liborphan.so -ldl -Wl,-R,.

I tried your testcase with binutils 2.30, which doesn't have Alan's patch:

[hjl@gnu-6 orphan-4]$ cat lib.c
extern int __start___verbose[];
extern int __stop___verbose[];
extern int foo2(void);
int foo (void)
{
  static int my_var __attribute__((section("__verbose"))) = 5;
  if (__start___verbose == __stop___verbose  // ref_regular
      || __start___verbose[0] != 5)
    return -1;
  else
    return 0;
}
[hjl@gnu-6 orphan-4]$ cat app.c
#include <stdlib.h>
#include <stdio.h>
extern int foo (void);
extern int __start___verbose[];
extern int __stop___verbose[];
int bar (void)
{
  static int my_var __attribute__((section("__verbose"))) = 6;
  // no ref_regular!
  return 0;
}

int main()
{
  if (bar () != 0)
    {
      printf("main: wrong __start___verbose\n");
      exit(2);
    }
  return 0;
}
[hjl@gnu-6 orphan-4]$ make
cc -g   -c -o app.o app.c
cc -B./ -o app app.o liborphan.so -ldl -Wl,-R,.
./app
[hjl@gnu-6 orphan-4]$

It looks good to me.  What am I missing?

-- 
H.J.