commit 00781d8096cfd74574cbe0f08f2618beae9ef84e
author Fangrui Song <maskray@google.com> Thu Dec 20 22:46:01 2018 +0000
committer Fangrui Song <maskray@google.com> Thu Dec 20 22:46:01 2018 +0000
tree c197fbd22ba7c2305517063b26bfabec64eaf501
parent b8be5f94d903639c982328c056250606f0adcf77

[ELF] Move IsNeeded logic from SymbolTable::addShared to MarkLive, and check IsUsedInRegularObj

Summary:
In glibc, libc.so is a linker script with an as-needed dependency on ld-linux-x86-64.so.2

    GROUP ( /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc_nonshared.a  AS_NEEDED ( /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ) )

ld-linux-x86-64.so.2 (as-needed) defines some symbols which resolve undefined references in libc.so.6, it will therefore be added as a DT_NEEDED entry, which isn't necessary.

The test case as-needed-not-in-regular.s emulates the libc.so scenario, where ld.bfd and gold don't add DT_NEEDED for a.so

The relevant code in gold/resolve.cc:

  // If we have a non-WEAK reference from a regular object to a
  // dynamic object, mark the dynamic object as needed.
  if (to->is_from_dynobj() && to->in_reg() && !to->is_undef_binding_weak())
    to->object()->set_is_needed();

in_reg() appears to do something similar to IsUsedInRegularObj.

This patch makes lld do the similar thing, but moves the check from
addShared to a later stage MarkLive where all symbols are scanned.

Reviewers: ruiu, pcc, espindola

Reviewed By: ruiu

Subscribers: emaste, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D55902

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@349849 91177308-0d34-0410-b5e6-96231b3b80d8