[lld] r298078 - [ELF] - Simplify logic of creating "COMMON" section.

[Rafael Avila de Espindola via llvm-commits]

I am now getting:

/home/fedora/llvm/llvm/tools/lld/ELF/Writer.cpp:361:24: warning: using the result of an assignment as a condition without parentheses [-Wparentheses]

Cheers,
Rafael


George Rimar via llvm-commits <llvm-commits at lists.llvm.org> writes:

> Author: grimar
> Date: Fri Mar 17 08:04:06 2017
> New Revision: 298078
>
> URL: http://llvm.org/viewvc/llvm-project?rev=298078&view=rev
> Log:
> [ELF] - Simplify logic of creating "COMMON" section.
>
> Patch reuses BssSection section to simplify creation of 
> COMMON section.
>
> Differential revision: https://reviews.llvm.org/D30690
>
> Modified:
>     lld/trunk/ELF/SyntheticSections.cpp
>     lld/trunk/ELF/SyntheticSections.h
>     lld/trunk/ELF/Writer.cpp
>
> Modified: lld/trunk/ELF/SyntheticSections.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SyntheticSections.cpp?rev=298078&r1=298077&r2=298078&view=diff
> ==============================================================================
> --- lld/trunk/ELF/SyntheticSections.cpp (original)
> +++ lld/trunk/ELF/SyntheticSections.cpp Fri Mar 17 08:04:06 2017
> @@ -63,33 +63,22 @@ template <class ELFT> static std::vector
>  
>  // Find all common symbols and allocate space for them.
>  template <class ELFT> InputSection *elf::createCommonSection() {
> -  auto *Ret = make<InputSection>(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 1,
> -                                 ArrayRef<uint8_t>(), "COMMON");
> -  Ret->Live = true;
> -
>    if (!Config->DefineCommon)
> -    return Ret;
> +    return nullptr;
>  
>    // Sort the common symbols by alignment as an heuristic to pack them better.
>    std::vector<DefinedCommon *> Syms = getCommonSymbols<ELFT>();
> +  if (Syms.empty())
> +    return nullptr;
> +
>    std::stable_sort(Syms.begin(), Syms.end(),
>                     [](const DefinedCommon *A, const DefinedCommon *B) {
>                       return A->Alignment > B->Alignment;
>                     });
> +  BssSection *Ret = make<BssSection>("COMMON");
> +  for (DefinedCommon *Sym : Syms)
> +    Sym->Offset = Ret->reserveSpace(Sym->Alignment, Sym->Size);
>  
> -  // Assign offsets to symbols.
> -  size_t Size = 0;
> -  uint32_t Alignment = 1;
> -  for (DefinedCommon *Sym : Syms) {
> -    Alignment = std::max(Alignment, Sym->Alignment);
> -    Size = alignTo(Size, Sym->Alignment);
> -
> -    // Compute symbol offset relative to beginning of input section.
> -    Sym->Offset = Size;
> -    Size += Sym->Size;
> -  }
> -  Ret->Alignment = Alignment;
> -  Ret->Data = makeArrayRef<uint8_t>(nullptr, Size);
>    return Ret;
>  }
>  
> @@ -380,7 +369,8 @@ BssSection::BssSection(StringRef Name)
>      : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 0, Name) {}
>  
>  size_t BssSection::reserveSpace(uint32_t Alignment, size_t Size) {
> -  OutSec->updateAlignment(Alignment);
> +  if (OutSec)
> +    OutSec->updateAlignment(Alignment);
>    this->Size = alignTo(this->Size, Alignment) + Size;
>    this->Alignment = std::max<uint32_t>(this->Alignment, Alignment);
>    return this->Size - Size;
>
> Modified: lld/trunk/ELF/SyntheticSections.h
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SyntheticSections.h?rev=298078&r1=298077&r2=298078&view=diff
> ==============================================================================
> --- lld/trunk/ELF/SyntheticSections.h (original)
> +++ lld/trunk/ELF/SyntheticSections.h Fri Mar 17 08:04:06 2017
> @@ -153,9 +153,10 @@ private:
>    uint8_t *HashBuf;
>  };
>  
> -// BssSection is used to reserve space for copy relocations. We create two
> -// instances of this class for .bss and .bss.rel.ro. .bss is used for writable
> -// symbols, and .bss.rel.ro is used for read-only symbols.
> +// BssSection is used to reserve space for copy relocations and common symbols.
> +// We create three instances of this class for .bss, .bss.rel.ro and "COMMON".
> +// .bss is used for writable symbols, .bss.rel.ro is used for read-only symbols
> +// and latter used for common symbols.
>  class BssSection final : public SyntheticSection {
>  public:
>    BssSection(StringRef Name);
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=298078&r1=298077&r2=298078&view=diff
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Fri Mar 17 08:04:06 2017
> @@ -358,11 +358,8 @@ template <class ELFT> void Writer<ELFT>:
>      Add(In<ELFT>::BuildId);
>    }
>  
> -  InputSection *Common = createCommonSection<ELFT>();
> -  if (!Common->Data.empty()) {
> -    In<ELFT>::Common = Common;
> -    Add(Common);
> -  }
> +  if (In<ELFT>::Common = createCommonSection<ELFT>())
> +    Add(In<ELFT>::Common);
>  
>    In<ELFT>::Bss = make<BssSection>(".bss");
>    Add(In<ELFT>::Bss);
>
>
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