Fangrui Song e32f04cdc9 [ELF] Parse SHT_GNU_verneed and respect versioned undefined symbols in shared objects ...

An undefined symbol in a shared object can be versioned, like `f@v1`.
We currently insert `f` as an Undefined into the symbol table, but we
should insert `f@v1` instead.

The string `v1` is inferred from SHT_GNU_versym and SHT_GNU_verneed.
This patch implements the functionality.

Failing to do this can cause two issues:

* If a versioned symbol referenced by a shared object is defined in the
  executable, we will fail to export it.
* If a versioned symbol referenced by a shared object in another object
  file, --no-allow-shlib-undefined may spuriously report an
  "undefined reference to " error. See https://bugs.llvm.org/show_bug.cgi?id=44842
  (Linking -lfftw3 -lm on Arch Linux can cause
  `undefined reference to __log_finite`)

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D80059

2020-05-23 09:55:48 -07:00

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