[Bug gcov-profile/96913] gcc-11: __gcov_merge_topn hangs

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96913

Sergei Trofimovich <slyfox at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2020-09-06
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |slyfox at gcc dot gnu.org

--- Comment #5 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
(In reply to Sergei Trofimovich from comment #4)

> $ x86_64-pc-linux-gnu-nm tauthon | fgrep gcov_merge_top
> 000000000040387f t __gcov_merge_topn
> $ x86_64-pc-linux-gnu-nm libtauthon2.8.so.1.0 | fgrep gcov_merge_top
> 000000000029a202 t __gcov_merge_topn
> 
> Don't know yet know where 'gi_ptr->merge' gets filled in to leak
> executable's symbol into binary.

Having looked at absolute addresses and address maps it's even more complicated
that that:

call trace:

tauthon : main()
 -> libtauthon2.8.so.1.0 : execve()
    ->libtauthon2.8.so.1.0 : __gcov_execve()
      ->libtauthon2.8.so.1.0 : write_one_data()


There addresses of:
    if (gi_ptr->merge[t_ix] == __gcov_merge_topn)
are:
- gi_ptr->merge[t_ix]: _struct.so:&__gcov_merge_topn
- __gcov_merge_topn: libtauthon2.8.so.1.0:&__gcov_merge_topn

Sent https://gcc.gnu.org/pipermail/gcc-patches/2020-September/553320.html for
review.

Claiming the bug.