[lld] r284010 - Alternative fix for reloc tareting discarded section

[Rui Ueyama via llvm-commits]

On Wed, Oct 12, 2016 at 5:31 AM, Eugene Leviant via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: evgeny777
> Date: Wed Oct 12 07:31:34 2016
> New Revision: 284010
>
> URL: http://llvm.org/viewvc/llvm-project?rev=284010&view=rev
> Log:
> Alternative fix for reloc tareting discarded section
>
> r283984 introduced a problem of too many warning messages being shown
> when -ffunction-sections and -fdata-sections were used in conjunction
> with --gc-sections linker flag and debugging information present. This
> happens because lot of relocations from .debug_line section may become
> invalid in such case. The newer fix doesn't show any warning message but
> zeroes OutSec pointer in createInputSectionList() to avoid crash, when
> relocations are written
>
> Modified:
>     lld/trunk/ELF/LinkerScript.cpp
>     lld/trunk/ELF/Symbols.cpp
>     lld/trunk/test/ELF/linkerscript/discard-section.s
>
> Modified: lld/trunk/ELF/LinkerScript.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/
> LinkerScript.cpp?rev=284010&r1=284009&r2=284010&view=diff
> ============================================================
> ==================
> --- lld/trunk/ELF/LinkerScript.cpp (original)
> +++ lld/trunk/ELF/LinkerScript.cpp Wed Oct 12 07:31:34 2016
> @@ -239,6 +239,12 @@ LinkerScript<ELFT>::createInputSectionLi
>        Ret.push_back(static_cast<InputSectionBase<ELFT> *>(S));
>    }
>
> +  // After we created final list we should now set OutSec pointer to null,
> +  // instead of -1. Otherwise we may get a crash when writing relocs, in
> +  // case section is discarded by linker script
> +  for (InputSectionBase<ELFT> *S : Ret)
> +    S->OutSec = nullptr;
>

I was thinking that it is an invariant that InputSection::OutSec always
points to an output section if the input section is included in the output
section, so I'm confused with this code and comment. How does it work?

+
>    return Ret;
>  }
>
>
> Modified: lld/trunk/ELF/Symbols.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.
> cpp?rev=284010&r1=284009&r2=284010&view=diff
> ============================================================
> ==================
> --- lld/trunk/ELF/Symbols.cpp (original)
> +++ lld/trunk/ELF/Symbols.cpp Wed Oct 12 07:31:34 2016
> @@ -25,12 +25,6 @@ using namespace lld;
>  using namespace lld::elf;
>
>  template <class ELFT>
> -static std::string getSectionName(InputSectionBase<ELFT> *S) {
> -  StringRef Filename = S->getFile()->getName();
> -  return (sys::path::filename(Filename) + "(" + S->Name + ")").str();
> -}
> -
> -template <class ELFT>
>  static typename ELFT::uint getSymVA(const SymbolBody &Body,
>                                      typename ELFT::uint &Addend) {
>    typedef typename ELFT::uint uintX_t;
> @@ -60,11 +54,6 @@ static typename ELFT::uint getSymVA(cons
>      if (!SC)
>        return D.Value;
>
> -    if (!SC->Live) {
> -      warn("relocation refers to discarded section '" +
> getSectionName(SC) + "'");
> -      return 0;
> -    }
> -
>      uintX_t Offset = D.Value;
>      if (D.isSection()) {
>        Offset += Addend;
>
> Modified: lld/trunk/test/ELF/linkerscript/discard-section.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/
> linkerscript/discard-section.s?rev=284010&r1=284009&r2=284010&view=diff
> ============================================================
> ==================
> --- lld/trunk/test/ELF/linkerscript/discard-section.s (original)
> +++ lld/trunk/test/ELF/linkerscript/discard-section.s Wed Oct 12 07:31:34
> 2016
> @@ -1,10 +1,9 @@
>  # REQUIRES: x86
>  # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
>  # RUN: echo "SECTIONS { /DISCARD/ : { *(.aaa*) } }" > %t.script
> -# RUN: ld.lld -o %t1 --script %t.script %t 2>&1 | FileCheck
> --check-prefix=WARN %s
> +# RUN: ld.lld -o %t1 --script %t.script %t
>  # RUN: llvm-objdump -section-headers %t1 | FileCheck %s
>
> -# WARN: relocation refers to discarded section {{.+}}(.aaa)
>  # CHECK-NOT: .aaa
>
>  .section .aaa,"a"
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20161012/7262c9ce/attachment.html>