[Bug ld/16457] New: Weak reference leads to bogus entry in .gnu.version_r section

[ldv at altlinux dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16457

            Bug ID: 16457
           Summary: Weak reference leads to bogus entry in .gnu.version_r
                    section
           Product: binutils
           Version: 2.24
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: ldv at altlinux dot org

Weak reference may cause ld to generate an entry in .gnu.version_r section that
would reference an object not present in the dynamic section.

This actually happens with most of c++ objects that have weak references to
versioned symbols from libpthread.
Here is an artificial test case without c++ and foreign libraries:

$ cat libb.c
int fb(void){return 0;}

$ cat libb.map
FOO{global:fb;};

$ gcc -shared -Wl,-soname,libb.so,--version-script,libb.map -Wall -Werror -fPIC
-o libb.so libb.c

$ cat liba.c 
int fb(void);
int fa(void){return fb();}

$ gcc -shared -Wl,--no-undefined,-soname,liba.so -Wall -Werror -fPIC -o liba.so
liba.c -L. -lb

$ cat e.c 
int fa(void);
int fb(void) __attribute__((weak));
int main(void){return fb?fb():fa();}

$ gcc -Wall -Werror e.c -Wl,--rpath-link,. -L. -la -o e

$ readelf -Wd e | grep -F NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [liba.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

$ readelf -WV e                  

Version symbols section '.gnu.version' contains 13 entries:
 Addr: 00000000004004e8  Offset: 0x0004e8  Link: 5 (.dynsym)
  000:   0 (*local*)       0 (*local*)       2 (GLIBC_2.2.5)   0 (*local*)    
  004:   0 (*local*)       0 (*local*)       0 (*local*)       1 (*global*)   
  008:   1 (*global*)      1 (*global*)      1 (*global*)      1 (*global*)   
  00c:   3 (FOO)        

Version needs section '.gnu.version_r' contains 2 entries:
 Addr: 0x0000000000400508  Offset: 0x000508  Link: 6 (.dynstr)
  000000: Version: 1  File: libb.so  Cnt: 1
  0x0010:   Name: FOO  Flags: none  Version: 3
  0x0020: Version: 1  File: libc.so.6  Cnt: 1
  0x0030:   Name: GLIBC_2.2.5  Flags: none  Version: 2

Note that there is no DT_NEEDED entry for libb.so, but the latter is referenced
from .gnu.version_r section.

Older ld versions used to add a DT_NEEDED entry in this case, see
https://sourceware.org/bugzilla/show_bug.cgi?id=15149

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