Objects not being replaced in thin archive

[Eric Dana]

I'm seeing symbol table issues when working with thin archives:
First, I create a regular archive:
$ ar -rcs libstuff a.out
 
Then I create a thin archive:
$ ar -vrcs -T libtest.a libstuff.a
a - a.out
$ nm libtest.a
 
a.out:
0000000000601034 B __bss_start
0000000000601034 b completed.6342
0000000000601030 D __data_start
0000000000601030 W data_start
0000000000400470 t deregister_tm_clones
00000000004004e0 t __do_global_dtors_aux
0000000000600e18 t __do_global_dtors_aux_fini_array_entry
00000000004005f8 R __dso_handle
0000000000600e28 d _DYNAMIC
0000000000601034 D _edata
0000000000601038 B _end
00000000004005e4 T _fini
0000000000400500 t frame_dummy
0000000000600e10 t __frame_dummy_init_array_entry
0000000000400730 r __FRAME_END__
0000000000601000 d _GLOBAL_OFFSET_TABLE_
                 w __gmon_start__
00000000004003e0 T _init
0000000000600e18 t __init_array_end
0000000000600e10 t __init_array_start
00000000004005f0 R _IO_stdin_used
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
0000000000600e20 d __JCR_END__
0000000000600e20 d __JCR_LIST__
                 w _Jv_RegisterClasses
00000000004005e0 T __libc_csu_fini
0000000000400570 T __libc_csu_init
                 U __libc_start_main@@GLIBC_2.2.5
0000000000400530 T main
                 U printf@@GLIBC_2.2.5
00000000004004a0 t register_tm_clones
0000000000400440 T _start
0000000000601038 D __TMC_END__
 
Now we update the thin archive:
ar -vrcs -T libtest.a libstuff.a
a - a.out
 
Note that the a.out was added, not replaced.
Now we look at the symbol table:
$ nm libtest.a
 
a.out:
0000000000601034 B __bss_start
0000000000601034 b completed.6342
0000000000601030 D __data_start
0000000000601030 W data_start
0000000000400470 t deregister_tm_clones
00000000004004e0 t __do_global_dtors_aux
0000000000600e18 t __do_global_dtors_aux_fini_array_entry
00000000004005f8 R __dso_handle
0000000000600e28 d _DYNAMIC
0000000000601034 D _edata
0000000000601038 B _end
00000000004005e4 T _fini
0000000000400500 t frame_dummy
0000000000600e10 t __frame_dummy_init_array_entry
0000000000400730 r __FRAME_END__
0000000000601000 d _GLOBAL_OFFSET_TABLE_
                 w __gmon_start__
00000000004003e0 T _init
0000000000600e18 t __init_array_end
0000000000600e10 t __init_array_start
00000000004005f0 R _IO_stdin_used
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
0000000000600e20 d __JCR_END__
0000000000600e20 d __JCR_LIST__
                 w _Jv_RegisterClasses
00000000004005e0 T __libc_csu_fini
0000000000400570 T __libc_csu_init
                 U __libc_start_main@@GLIBC_2.2.5
0000000000400530 T main
                 U printf@@GLIBC_2.2.5
00000000004004a0 t register_tm_clones
0000000000400440 T _start
0000000000601038 D __TMC_END__
 
a.out:
0000000000601034 B __bss_start
0000000000601034 b completed.6342
0000000000601030 D __data_start
0000000000601030 W data_start
0000000000400470 t deregister_tm_clones
00000000004004e0 t __do_global_dtors_aux
0000000000600e18 t __do_global_dtors_aux_fini_array_entry
00000000004005f8 R __dso_handle
0000000000600e28 d _DYNAMIC
0000000000601034 D _edata
0000000000601038 B _end
00000000004005e4 T _fini
0000000000400500 t frame_dummy
0000000000600e10 t __frame_dummy_init_array_entry
0000000000400730 r __FRAME_END__
0000000000601000 d _GLOBAL_OFFSET_TABLE_
                 w __gmon_start__
00000000004003e0 T _init
0000000000600e18 t __init_array_end
0000000000600e10 t __init_array_start
00000000004005f0 R _IO_stdin_used
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
0000000000600e20 d __JCR_END__
0000000000600e20 d __JCR_LIST__
                 w _Jv_RegisterClasses
00000000004005e0 T __libc_csu_fini
0000000000400570 T __libc_csu_init
                 U __libc_start_main@@GLIBC_2.2.5
0000000000400530 T main
                 U printf@@GLIBC_2.2.5
00000000004004a0 t register_tm_clones
0000000000400440 T _start
0000000000601038 D __TMC_END__
Segmentation fault (core dumped)
 
(Note: the segmentation fault occurs on RHEL 6.9, not RHEL 7.6) Looking at the symbol table, a.out is there twice!
On RHEL 6.9, if I try to update (not create) another thin library with 'upd= ated' libtest.a, 'ar' loops forever.
If I used an object file as input, rather than another library, to update t= he thin library libtest.a, the object would be replaced in the library, rat= her than being added.
 
So, two issues:
 
1.       When updating libtest.a, should a.out have been replaced or added?
 
2.       Why are there 2 a.out symbol tables?
 
Eric Dana
eric@eidana.com