[PATCH] D34800: [ELF] Remove unused synthetic sections from script commands

[Petr Hosek via llvm-commits]

Done, sorry about the delay I was on vacation for a few days.

On Mon, Jul 3, 2017 at 8:22 AM Rafael Avila de Espindola <
rafael.espindola at gmail.com> wrote:

> Is anything blocking committing this?
>
> Cheers,
> Rafael
>
> Rafael Avila de Espindola <rafael.espindola at gmail.com> writes:
>
> > LGTM, thanks!
> >
> > Cheers,
> > Rafael
> >
> > Petr Hosek via Phabricator via llvm-commits
> > <llvm-commits at lists.llvm.org> writes:
> >
> >> phosek created this revision.
> >> phosek added a project: lld.
> >> Herald added a subscriber: emaste.
> >>
> >> Script commands are processed before unused synthetic sections are
> >> removed. Therefore, if a linker script matches one of these sections
> >> it'll get emitted as an empty output section because the logic for
> >> removing unused synthetic sections ignores script commands which
> >> could have already matched and captured one of these sections. This
> >> patch fixes that by also removing the unused synthetic sections from
> >> the script commands.
> >>
> >>
> >> Repository:
> >>   rL LLVM
> >>
> >> https://reviews.llvm.org/D34800
> >>
> >> Files:
> >>   ELF/Writer.cpp
> >>   test/ELF/linkerscript/unused-synthetic.s
> >>
> >>
> >> Index: test/ELF/linkerscript/unused-synthetic.s
> >> ===================================================================
> >> --- /dev/null
> >> +++ test/ELF/linkerscript/unused-synthetic.s
> >> @@ -0,0 +1,18 @@
> >> +# REQUIRES: x86
> >> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> >> +# RUN: echo "SECTIONS { \
> >> +# RUN:    .got  : { *(.got) } \
> >> +# RUN:    .plt  : { *(.plt) } \
> >> +# RUN:    .text : { *(.text) } \
> >> +# RUN:  }" > %t.script
> >> +# RUN: ld.lld -shared -o %t.so --script %t.script %t.o
> >> +
> >> +# RUN: llvm-objdump -section-headers %t.so | FileCheck %s
> >> +# CHECK-NOT:  .got
> >> +# CHECK-NOT:  .plt
> >> +# CHECK:      .text
> >> +# CHECK-NEXT: .dynsym
> >> +
> >> +.global _start
> >> +_start:
> >> +  nop
> >> Index: ELF/Writer.cpp
> >> ===================================================================
> >> --- ELF/Writer.cpp
> >> +++ ELF/Writer.cpp
> >> @@ -1149,8 +1149,17 @@
> >>      SS->Live = false;
> >>      // If there are no other sections in the output section, remove it
> from the
> >>      // output.
> >> -    if (OS->Sections.empty())
> >> +    if (OS->Sections.empty()) {
> >>        V.erase(std::find(V.begin(), V.end(), OS));
> >> +      // Also remove script commands matching the output section.
> >> +      auto &Cmds = Script->Opt.Commands;
> >> +      auto I = std::remove_if(Cmds.begin(), Cmds.end(),
> [&](BaseCommand *Cmd) {
> >> +        if (auto *OSCmd = dyn_cast<OutputSectionCommand>(Cmd))
> >> +          return OSCmd->Sec == OS;
> >> +        return false;
> >> +      });
> >> +      Cmds.erase(I, Cmds.end());
> >> +    }
> >>    }
> >>  }
> >>
> >>
> >>
> >> Index: test/ELF/linkerscript/unused-synthetic.s
> >> ===================================================================
> >> --- /dev/null
> >> +++ test/ELF/linkerscript/unused-synthetic.s
> >> @@ -0,0 +1,18 @@
> >> +# REQUIRES: x86
> >> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> >> +# RUN: echo "SECTIONS { \
> >> +# RUN:    .got  : { *(.got) } \
> >> +# RUN:    .plt  : { *(.plt) } \
> >> +# RUN:    .text : { *(.text) } \
> >> +# RUN:  }" > %t.script
> >> +# RUN: ld.lld -shared -o %t.so --script %t.script %t.o
> >> +
> >> +# RUN: llvm-objdump -section-headers %t.so | FileCheck %s
> >> +# CHECK-NOT:  .got
> >> +# CHECK-NOT:  .plt
> >> +# CHECK:      .text
> >> +# CHECK-NEXT: .dynsym
> >> +
> >> +.global _start
> >> +_start:
> >> +  nop
> >> Index: ELF/Writer.cpp
> >> ===================================================================
> >> --- ELF/Writer.cpp
> >> +++ ELF/Writer.cpp
> >> @@ -1149,8 +1149,17 @@
> >>      SS->Live = false;
> >>      // If there are no other sections in the output section, remove it
> from the
> >>      // output.
> >> -    if (OS->Sections.empty())
> >> +    if (OS->Sections.empty()) {
> >>        V.erase(std::find(V.begin(), V.end(), OS));
> >> +      // Also remove script commands matching the output section.
> >> +      auto &Cmds = Script->Opt.Commands;
> >> +      auto I = std::remove_if(Cmds.begin(), Cmds.end(),
> [&](BaseCommand *Cmd) {
> >> +        if (auto *OSCmd = dyn_cast<OutputSectionCommand>(Cmd))
> >> +          return OSCmd->Sec == OS;
> >> +        return false;
> >> +      });
> >> +      Cmds.erase(I, Cmds.end());
> >> +    }
> >>    }
> >>  }
> >>
> >> _______________________________________________
> >> llvm-commits mailing list
> >> llvm-commits at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
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