lld: symbols with version index 0 shouldn't be changed to local symbol

[hjl-tools]

Oracle Solaris 11.4 Linker and Libraries Guide:

https://docs.oracle.com/en/operating-systems/solaris/oracle-solaris/11.4/linkers-libraries/version-symbol-section.html

defines VER_NDX_LOCAL to 0 with a comment, "Symbol has local scope". This
leads to different interpretations by different linker implementations.
However Solaris as well as ld and ld.so in glibc always treat symbols
with version index 0 as unversioned symbols, defined or undefined, with
global visibility. As discussed in

https://sourceware.org/bugzilla/show_bug.cgi?id=33577

in hindsight, VER_NDX_NONE might be a better name. Ali from Oracle is
working on clarifying what version index 0 really means for unversioned
symbols, defined or undefined, with global visibility. Symbols with version
index 0 should be treated as unversioned without making them a local symbol.

[hjl-tools]

A patch to treat symbols with version index 0 as unversioned without making them a local symbol:
0001-lld-Treat-symbols-with-version-index-0-as-unversione.patch

[MaskRay]

See #168189

I created #168189 with rationale why using index 0 makes sense (GNU ld has used index 0 for unversioned undefined symbols both before
version 2.35 (see sourceware.org/PR26002) and in the upcoming
2.46 release (see sourceware.org/PR33577)) before I saw your patch. 0001-lld-Treat-symbols-with-version-index-0-as-unversione.patch has an issue: we should retain the error for dynamic symbols defined with VER_NDX_LOCAL, as intended. While I've heard that GNU ld may emit VER_NDX_LOCAL for defined dynamic symbols on ia64, llvm-project does not support or need to address that specific target.

[llvmbot]

@llvm/issue-subscribers-lld-elf

Author: None (hjl-tools)

Oracle Solaris 11.4 Linker and Libraries Guide:

https://docs.oracle.com/en/operating-systems/solaris/oracle-solaris/11.4/linkers-libraries/version-symbol-section.html

defines VER_NDX_LOCAL to 0 with a comment, "Symbol has local scope". This
leads to different interpretations by different linker implementations.
However Solaris as well as ld and ld.so in glibc always treat symbols
with version index 0 as unversioned symbols, defined or undefined, with
global visibility. As discussed in

https://sourceware.org/bugzilla/show_bug.cgi?id=33577

in hindsight, VER_NDX_NONE might be a better name. Ali from Oracle is
working on clarifying what version index 0 really means for unversioned
symbols, defined or undefined, with global visibility. Symbols with version
index 0 should be treated as unversioned without making them a local symbol.