[PATCH v3] elf: Don't set its DT_VERSYM entry for unversioned symbol

[Michael Matz]

Hello,

On Wed, 12 Nov 2025, Andreas Schwab wrote:

> > Two values are reserved:
> >
> >   VER_NDX_LOCAL  0 - The symbol is private, and is not available
> > outside this object.
> 
> Doesn't this mean that the mold behaviour is correct?

I agree.  That numeric value '1' (instead of '0') is the default value (as 
the version to use when nothing particularly interesting is specified) is 
a wart, but one that we now need to follow.  If version info must be 
encoded then a global undefined symbol without a version requirement has 
to continue using value 1.

> $ binutils/readelf -WDsV c.so
> 
> Symbol table for image contains 9 entries:
>    Num:    Value          Size Type    Bind   Vis      Ndx Name
>      0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
>      1: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_deregisterTMCloneTable
>      2: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND printf@GLIBC_2.2.5 (2)
>      3: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__
>      4: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_registerTMCloneTable
>      5: 0000000000000000     0 FUNC    WEAK   DEFAULT  UND __cxa_finalize@GLIBC_2.2.5 (2)
>      6: 0000000000004010    56 OBJECT  GLOBAL DEFAULT   21 ext_var
>      7: 000000000000112a    43 FUNC    GLOBAL DEFAULT   12 print
>      8: 0000000000001155    46 FUNC    GLOBAL DEFAULT   12 print64
> 
> Version symbols section '.gnu.version' contains 9 entries:
>  Addr: 0x0000000000000390  Offset: 0x00000390  Link: 3 (.dynsym)
>   000:   0 (*local*)       0 (*local*)       2 (GLIBC_2.2.5)   0 (*local*)    
>   004:   0 (*local*)       2 (GLIBC_2.2.5)   0 (*local*)       0 (*local*)    
>   008:   0 (*local*)    

I also don't see justification for the WEAK undefined symbols to be 
'local' here.  IMO they all should be value 1.  If that means that we 
can't differentiate between a symbol definition of 'foo' vs 'foo@' 
(with empty version), then that's what we need to pay.  Alternatively an 
explicitely empty version with a different value than 1 could be 
introduced to record the difference, but that seems unhelpfully quirky.


Ciao,
Michael.