[lld] r260460 - ELF: Implement __attribute__((init_priority(N)) support.

[Sean Silva via llvm-commits]

Did you intend to add .[cd]tors support also? That was part of PR26538.

-- Sean Silva

On Wed, Feb 10, 2016 at 3:20 PM, Rui Ueyama via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: ruiu
> Date: Wed Feb 10 17:20:42 2016
> New Revision: 260460
>
> URL: http://llvm.org/viewvc/llvm-project?rev=260460&view=rev
> Log:
> ELF: Implement __attribute__((init_priority(N)) support.
>
> Added:
>     lld/trunk/test/ELF/init_fini_priority.s
> Modified:
>     lld/trunk/ELF/OutputSections.cpp
>     lld/trunk/ELF/OutputSections.h
>     lld/trunk/ELF/Writer.cpp
>
> Modified: lld/trunk/ELF/OutputSections.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=260460&r1=260459&r2=260460&view=diff
>
> ==============================================================================
> --- lld/trunk/ELF/OutputSections.cpp (original)
> +++ lld/trunk/ELF/OutputSections.cpp Wed Feb 10 17:20:42 2016
> @@ -750,6 +750,44 @@ void OutputSection<ELFT>::addSection(Inp
>    this->Header.sh_size = Off;
>  }
>
> +// If an input string is in the form of "foo.N" where N is a number,
> +// return N. Otherwise, returns 65536, which is one greater than the
> +// lowest priority.
> +static int getPriority(StringRef S) {
> +  size_t Pos = S.rfind('.');
> +  if (Pos == StringRef::npos)
> +    return 65536;
> +  int V;
> +  if (S.substr(Pos + 1).getAsInteger(10, V))
> +    return 65536;
> +  return V;
> +}
> +
> +// Sorts input sections by section name suffixes, so that .foo.N comes
> +// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
> +// For more detail, read the section of the GCC's manual about
> init_priority.
> +template <class ELFT> void OutputSection<ELFT>::sortByPriority() {
> +  // Sort sections by priority.
> +  typedef std::pair<int, InputSection<ELFT> *> Pair;
> +  std::vector<Pair> V;
> +  for (InputSection<ELFT> *S : Sections)
> +    V.push_back({getPriority(S->getSectionName()), S});
> +  std::sort(V.begin(), V.end(),
> +            [](const Pair &A, const Pair &B) { return A.first < B.first;
> });
> +  Sections.clear();
> +  for (Pair &P : V)
> +    Sections.push_back(P.second);
> +
> +  // Reassign section addresses.
> +  uintX_t Off = 0;
> +  for (InputSection<ELFT> *S : Sections) {
> +    Off = alignTo(Off, S->getAlign());
> +    S->OutSecOff = Off;
> +    Off += S->getSize();
> +  }
> +  this->Header.sh_size = Off;
> +}
> +
>  // Returns a VA which a relocatin RI refers to. Used only for local
> symbols.
>  // For non-local symbols, use SymbolBody::getVA instead.
>  template <class ELFT, bool IsRela>
>
> Modified: lld/trunk/ELF/OutputSections.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=260460&r1=260459&r2=260460&view=diff
>
> ==============================================================================
> --- lld/trunk/ELF/OutputSections.h (original)
> +++ lld/trunk/ELF/OutputSections.h Wed Feb 10 17:20:42 2016
> @@ -279,6 +279,7 @@ public:
>    typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
>    OutputSection(StringRef Name, uint32_t sh_type, uintX_t sh_flags);
>    void addSection(InputSectionBase<ELFT> *C) override;
> +  void sortByPriority();
>    void writeTo(uint8_t *Buf) override;
>
>  private:
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=260460&r1=260459&r2=260460&view=diff
>
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Wed Feb 10 17:20:42 2016
> @@ -735,6 +735,10 @@ StringRef Writer<ELFT>::getOutputSection
>      return ".data";
>    if (S.startswith(".bss."))
>      return ".bss";
> +  if (S.startswith(".init_array."))
> +    return ".init_array";
> +  if (S.startswith(".fini_array."))
> +    return ".fini_array";
>    return S;
>  }
>
> @@ -915,6 +919,13 @@ template <class ELFT> void Writer<ELFT>:
>        Symtab.addAbsolute("end", ElfSym<ELFT>::End);
>  }
>
> +// Sort input sections by section name suffixes for
> +// __attribute__((init_priority(N))).
> +template <class ELFT> static void sortByPriority(OutputSectionBase<ELFT>
> *S) {
> +  if (S)
> +    reinterpret_cast<OutputSection<ELFT> *>(S)->sortByPriority();
> +}
> +
>  // Create output section objects and add them to OutputSections.
>  template <class ELFT> bool Writer<ELFT>::createSections() {
>    OutputSections.push_back(Out<ELFT>::ElfHeader);
> @@ -962,6 +973,10 @@ template <class ELFT> bool Writer<ELFT>:
>    Out<ELFT>::Dynamic->FiniArraySec =
>        Factory.lookup(".fini_array", SHT_FINI_ARRAY, SHF_WRITE |
> SHF_ALLOC);
>
> +  // Sort section contents for __attribute__((init_priority(N)).
> +  sortByPriority(Out<ELFT>::Dynamic->InitArraySec);
> +  sortByPriority(Out<ELFT>::Dynamic->FiniArraySec);
> +
>    // The linker needs to define SECNAME_start, SECNAME_end and
> SECNAME_stop
>    // symbols for sections, so that the runtime can get the start and end
>    // addresses of each section by section name. Add such symbols.
>
> Added: lld/trunk/test/ELF/init_fini_priority.s
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/init_fini_priority.s?rev=260460&view=auto
>
> ==============================================================================
> --- lld/trunk/test/ELF/init_fini_priority.s (added)
> +++ lld/trunk/test/ELF/init_fini_priority.s Wed Feb 10 17:20:42 2016
> @@ -0,0 +1,29 @@
> +// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
> +// RUN: ld.lld %t -o %t.exe
> +// RUN: llvm-objdump -s %t.exe | FileCheck %s
> +// REQUIRES: x86
> +
> +.globl _start
> +_start:
> +  nop
> +
> +.section .init_array, "aw", @init_array
> +  .align 8
> +  .byte 1
> +.section .init_array.100, "aw", @init_array
> +  .long 2
> +.section .init_array.5, "aw", @init_array
> +  .byte 3
> +
> +.section .fini_array, "aw", @fini_array
> +  .align 8
> +  .byte 4
> +.section .fini_array.100, "aw", @fini_array
> +  .long 5
> +.section .fini_array.5, "aw", @fini_array
> +  .byte 6
> +
> +// CHECK:      Contents of section .init_array:
> +// CHECK-NEXT: 03020000 00000000 01
> +// CHECK:      Contents of section .fini_array:
> +// CHECK-NEXT: 06050000 00000000 04
>
>
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