[Bug gold/18703] Symbol version and Version script incompatibility with BFD ld

[tmsriram at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18703

--- Comment #2 from Sriraman Tallam <tmsriram at google dot com> ---
On Tue, Jul 21, 2015 at 11:03 AM, ccoutant at gmail dot com
<address@hidden> wrote:
> https://sourceware.org/bugzilla/show_bug.cgi?id=18703
>
> --- Comment #1 from Cary Coutant <ccoutant at gmail dot com> ---
> You're looking at the linker symbol table with nm. (And nm does not show
> versioning information from the .gnu.version* sections.)
>
> When I build this with gold, readelf -Vs shows:
>
> Symbol table '.dynsym' contains 13 entries:
>    Num:    Value          Size Type    Bind   Vis      Ndx Name
>      0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
>      1: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__
>      2: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND
> _ITM_deregisterTMCloneTab
>      3: 0000000000000000     0 FUNC    WEAK   DEFAULT  UND
> address@hidden (3)
>      4: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND
> _ITM_registerTMCloneTable
>      5: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _Jv_RegisterClasses
>      6: 00000000000006f5    11 FUNC    GLOBAL DEFAULT   12 foo@@VERS_1.1
>      7: 0000000000002018     0 NOTYPE  GLOBAL DEFAULT  ABS _edata
>      8: 0000000000002019     0 NOTYPE  GLOBAL DEFAULT  ABS _end
>      9: 00000000000005c0     0 FUNC    GLOBAL DEFAULT   10 _init
>     10: 0000000000002018     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_start
>     11: 0000000000000700     0 FUNC    GLOBAL DEFAULT   13 _fini
>     12: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS VERS_1.1
>
> ...
>
> Version symbols section '.gnu.version' contains 13 entries:
>  Addr: 0000000000000458  Offset: 0x000458  Link: 2 (.dynsym)
>   000:   0 (*local*)       0 (*local*)       0 (*local*)       3 (GLIBC_2.2.5)
>   004:   0 (*local*)       0 (*local*)       2 (VERS_1.1)      1 (*global*)
>   008:   1 (*global*)      1 (*global*)      1 (*global*)      1 (*global*)
>   00c:   2 (VERS_1.1)
>
> Version definition section '.gnu.version_d' contains 2 entries:
>   Addr: 0x0000000000000474  Offset: 0x000474  Link: 3 (.dynstr)  000000: Rev: 
> 1
>  Flags: BASE   Index: 1  Cnt: 1  Name: ver1.so
>   0x001c: Rev: 1  Flags: none  Index: 2  Cnt: 1  Name: VERS_1.1
>
> Version needs section '.gnu.version_r' contains 1 entries:
>  Addr: 0x00000000000004ac  Offset: 0x0004ac  Link: 3 (.dynstr)
>   000000: Version: 1  File: libc.so.6  Cnt: 1
>   0x0010:   Name: GLIBC_2.2.5  Flags: none  Version: 3
>
> I think this is working as intended, although comparing with Gnu ld output, I
> see that gold defines it as a default version ("@@") where Gnu ld does not. 
> I'm
> not sure what the logic ought to be for that. Without the __asm__ in the .c
> file, Gnu ld also makes it a default version.

Some context:

https://gcc.gnu.org/ml/gcc-patches/2015-04/msg00878.html

This was used to hide symbols __cpu_indicator_init and __cpu_model
defined in libgcc_s.so so that this symbol is always obtained from
libgcc.a. Now, this works with GNU ld and not with gold.  Isnt this an
incompatibility. If this is not well defined, is there another well
defined way of achieving the same result?

Thanks
Sri


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