tree b3cd638683dde9da7e5ab5e1ade304cd7956d2c2
parent 1f1de38b0686fc0793d5c7afac9e99e05b4c5c3e
author Fangrui Song <maskray@google.com> 1568991801 +0000
committer Fangrui Song <maskray@google.com> 1568991801 +0000

[ELF] Error if the linked-to section of a SHF_LINK_ORDER section is discarded

Summary:
If st_link(A)=B, and A has the SHF_LINK_ORDER flag, we may dereference
a null pointer if B is garbage collected (PR43147):

1. In Wrter.cpp:compareByFilePosition, `aOut->sectionIndex` or `bOut->sectionIndex`
2. In OutputSections::finalize, `d->getParent()->sectionIndex`

Simply error and bail out to avoid null pointer dereferences. ld.bfd has
a similar error:

    sh_link of section `.bar' points to discarded section `.foo0' of `a.o'

ld.bfd is more permissive in that it just checks whether the linked-to
section of the first input section is discarded. This is likely because
it sets sh_link of the output section according to the first input
section.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D67761

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@372400 91177308-0d34-0410-b5e6-96231b3b80d8