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

H.J. Lu hjl.tools@gmail.com
Mon Jan 29 23:28:00 GMT 2018


On Mon, Jan 29, 2018 at 3:14 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Jan 29, 2018 at 2:58 PM, Michael Matz <matz@suse.de> wrote:
>> Hi,
>>
>> On Mon, 29 Jan 2018, H.J. Lu wrote:
>>
>>> > Yes, that's it.  (the associated lib.c needs to have a regular ref
>>> > symbol to __start___symbol and that lib needs to have something else
>>> > than "6" in its __verbose section, in order to test the exact
>>> > situation of pacemaker). With the patch from Alan ./app will have
>>> > __start___verbose in its symbol table, but not yet in the dynamic
>>> > symbol table.  So with only Alans patch -E would be necessary.  With
>>> > the addition of the bfd_elf_link_record_dynamic_symbol() call to
>>> > bfd_elf_define_start_stop the above testcase will start working as is
>>> > even without -E.
>>>
>>> I don't think Alan's patch nor yours are correct.  Here is mine with
>>> your testcase.  OK for master?
>>
>> In which way is the combination not correct?  I.e. make a testcase that
>> doesn't work with our stuff but with yours.
>>
>> (Note, in order for the semantics to be the same as before 2.29, these
>> symbols must not be created if there's neither a ref_regular ref, nor a
>> dynamic definition in any of the shared libs on the link cmdline).
>>
>
> I asked specially if the testcase is correct:
>
> https://sourceware.org/ml/binutils/2018-01/msg00421.html
>
> There is no reference to __start___verbose from executable nor
> from dynamic object.
>
> BTW, your patch:
>
> https://sourceware.org/ml/binutils/2018-01/msg00416.html
>
> may make .startof symbols dynamic.
>

And your patch doesn't work for:

https://sourceware.org/ml/binutils/2018-01/msg00421.html

[hjl@gnu-6 orphan-4]$ cat app.c
#define _GNU_SOURCE
#include <stdio.h>
#include <dlfcn.h>

extern int __start___verbose[];
extern int __stop___verbose[];
int bar (void)
{
  static int my_var __attribute__((section("__verbose"), used)) = 6;
  int *ptr;
  ptr = (int*) dlsym(RTLD_DEFAULT, "__start___verbose");
  if (!ptr || *ptr != 6)
    return -1;
  return 0;
}

int main()
{
  if (bar () != 0)
    {
      printf("main: wrong __start___verbose\n");
      return 2;
    }
  return 0;
}
[hjl@gnu-6 orphan-4]$ make
cc -g -O2   -c -o app.o app.c
cc -B./ -Wl,--gc-sections -o app app.o -ldl -Wl,-R,.
./app
main: wrong __start___verbose
make: *** [Makefile:9: all] Error 2
[hjl@gnu-6 orphan-4]$


-- 
H.J.



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