[PATCH] D32289: [ELF] - Linkerscript: support combination of linkerscript and --compress-debug-sections.

[Rafael Avila de Espindola via llvm-commits]

LGTM

George Rimar via Phabricator <reviews at reviews.llvm.org> writes:

> grimar updated this revision to Diff 97803.
> grimar added a comment.
>
> - Added check that shows we **do** compression of debug sections if linker script was used.
>
>
> https://reviews.llvm.org/D32289
>
> Files:
>   ELF/LinkerScript.cpp
>   ELF/OutputSections.cpp
>   test/ELF/linkerscript/Inputs/compress-debug-sections.s
>   test/ELF/linkerscript/compress-debug-sections.s
>
> Index: test/ELF/linkerscript/compress-debug-sections.s
> ===================================================================
> --- test/ELF/linkerscript/compress-debug-sections.s
> +++ test/ELF/linkerscript/compress-debug-sections.s
> @@ -0,0 +1,36 @@
> +# REQUIRES: x86, zlib
> +
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux \
> +# RUN:   %S/Inputs/compress-debug-sections.s -o %t1.o
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t2.o
> +
> +## .debug_str section is mergeable. LLD would combine all of them into single
> +## mergeable synthetic section. We use -O0 here to disable merging, that
> +## allows to check that input sections has correctly assigned offsets.
> +
> +# RUN: echo "SECTIONS { }" > %t.script
> +# RUN: ld.lld -O0 %t1.o %t2.o %t.script -o %t1 --compress-debug-sections=zlib
> +# RUN: llvm-dwarfdump %t1 | FileCheck %s
> +# RUN: llvm-readobj -s %t1 | FileCheck %s --check-prefix=ZLIBFLAGS
> +
> +# RUN: echo "SECTIONS { .debug_str 0 : { *(.debug_str) } }" > %t2.script
> +# RUN: ld.lld -O0 %t1.o %t2.o %t2.script -o %t2 --compress-debug-sections=zlib
> +# RUN: llvm-dwarfdump %t2 | FileCheck %s
> +# RUN: llvm-readobj -s %t2 | FileCheck %s --check-prefix=ZLIBFLAGS
> +
> +# CHECK:       .debug_str contents:
> +# CHECK-NEXT:    CCC
> +# CHECK-NEXT:    DDD
> +# CHECK-NEXT:    AAA
> +# CHECK-NEXT:    BBB
> +
> +# ZLIBFLAGS:       Section {
> +# ZLIBFLAGS:         Index:
> +# ZLIBFLAGS:         Name: .debug_str
> +# ZLIBFLAGS-NEXT:    Type: SHT_PROGBITS
> +# ZLIBFLAGS-NEXT:    Flags [
> +# ZLIBFLAGS-NEXT:      SHF_COMPRESSED
> +
> +.section .debug_str
> +  .asciz "AAA"
> +  .asciz "BBB"
> Index: test/ELF/linkerscript/Inputs/compress-debug-sections.s
> ===================================================================
> --- test/ELF/linkerscript/Inputs/compress-debug-sections.s
> +++ test/ELF/linkerscript/Inputs/compress-debug-sections.s
> @@ -0,0 +1,3 @@
> +.section .debug_str
> +  .asciz "CCC"
> +  .asciz "DDD"
> Index: ELF/OutputSections.cpp
> ===================================================================
> --- ELF/OutputSections.cpp
> +++ ELF/OutputSections.cpp
> @@ -139,12 +139,24 @@
>    this->Info = S->OutSec->SectionIndex;
>  }
>  
> +static uint64_t updateOffset(uint64_t Off, InputSection *S) {
> +  Off = alignTo(Off, S->Alignment);
> +  S->OutSecOff = Off;
> +  return Off + S->getSize();
> +}
> +
>  void OutputSection::addSection(InputSection *S) {
>    assert(S->Live);
>    Sections.push_back(S);
>    S->OutSec = this;
>    this->updateAlignment(S->Alignment);
>  
> +  // The actual offsets will be computed by assignAddresses. For now, use
> +  // crude approximation so that it is at least easy for other code to know the
> +  // section order. It is also used to calculate the output section size early
> +  // for compressed debug sections.
> +  this->Size = updateOffset(Size, S);
> +
>    // If this section contains a table of fixed-size entries, sh_entsize
>    // holds the element size. Consequently, if this contains two or more
>    // input sections, all of them must have the same sh_entsize. However,
> @@ -159,11 +171,8 @@
>  // and scan relocations to setup sections' offsets.
>  void OutputSection::assignOffsets() {
>    uint64_t Off = 0;
> -  for (InputSection *S : Sections) {
> -    Off = alignTo(Off, S->Alignment);
> -    S->OutSecOff = Off;
> -    Off += S->getSize();
> -  }
> +  for (InputSection *S : Sections)
> +    Off = updateOffset(Off, S);
>    this->Size = Off;
>  }
>  
> Index: ELF/LinkerScript.cpp
> ===================================================================
> --- ELF/LinkerScript.cpp
> +++ ELF/LinkerScript.cpp
> @@ -406,15 +406,8 @@
>        }
>  
>        // Add input sections to an output section.
> -      unsigned Pos = 0;
> -      for (InputSectionBase *S : V) {
> -        // The actual offset will be computed during
> -        // assignAddresses. For now, use the index as a very crude
> -        // approximation so that it is at least easy for other code to
> -        // know the section order.
> -        cast<InputSection>(S)->OutSecOff = Pos++;
> +      for (InputSectionBase *S : V)
>          Factory.addInputSec(S, Cmd->Name, Cmd->Sec);
> -      }
>      }
>    }
>    CurOutSec = nullptr;
> @@ -641,6 +634,11 @@
>      Dot = CurMemRegion->Offset;
>    switchTo(Sec);
>  
> +  // We do not support custom layout for compressed debug sectons.
> +  // At this point we already know their size and have compressed content.
> +  if (CurOutSec->Flags & SHF_COMPRESSED)
> +    return;
> +
>    for (BaseCommand *C : Cmd->Commands)
>      process(*C);
>  }