[lld] r232866 - [ELF] OrderPass : Order atoms only by ordinals.
Rui Ueyama
ruiu at google.com
Fri Mar 20 17:22:01 PDT 2015
This is non-trivial change, you should have sent this to pre-commit review.
Please do so next time. This change sacrificed readability a bit. Also, I
believe there's a bug in the code.
On Fri, Mar 20, 2015 at 4:47 PM, Shankar Easwaran <shankare at codeaurora.org>
wrote:
> Author: shankare
> Date: Fri Mar 20 18:47:03 2015
> New Revision: 232866
>
> URL: http://llvm.org/viewvc/llvm-project?rev=232866&view=rev
> Log:
> [ELF] OrderPass : Order atoms only by ordinals.
>
> Move the init array/fini array sorting to the Output ELF writer.
>
> AFAIK, this is only needed by the X86_64/ARM ABI.
>
> This shaves time taken to self host lld by 0.2 seconds.
>
> Before patch
> ----------------
> 4791.062059 task-clock # 1.634 CPUs utilized
> ( +- 0.28% )
> 61,107 context-switches # 0.013 M/sec
> ( +- 0.56% )
> 2.932902671 seconds time elapsed
> ( +- 0.84% )
>
> After patch
> -------------
> 4608.417248 task-clock # 1.669 CPUs utilized
> ( +- 0.30% )
> 61,616 context-switches # 0.013 M/sec
> ( +- 0.63% )
> 2.761012703 seconds time elapsed
> ( +- 0.63% )
>
> Modified:
> lld/trunk/lib/ReaderWriter/ELF/DefaultLayout.h
> lld/trunk/lib/ReaderWriter/ELF/OrderPass.h
> lld/trunk/lib/ReaderWriter/ELF/X86_64/X86_64TargetHandler.h
> lld/trunk/test/elf/init_array-order.test
>
> Modified: lld/trunk/lib/ReaderWriter/ELF/DefaultLayout.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/DefaultLayout.h?rev=232866&r1=232865&r2=232866&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/ELF/DefaultLayout.h (original)
> +++ lld/trunk/lib/ReaderWriter/ELF/DefaultLayout.h Fri Mar 20 18:47:03 2015
> @@ -316,13 +316,25 @@ public:
> return _copiedDynSymNames.count(sla->name());
> }
>
> + /// \brief Handle SORT_BY_PRIORITY.
> + void sortOutputSectionByPriority(StringRef outputSectionName,
> + StringRef prefix);
> +
> protected:
> + /// \brief TargetLayouts may use these functions to reorder the input
> sections
> + /// in a order defined by their ABI.
> + virtual void finalizeOutputSectionLayout() {}
> +
> /// \brief Allocate a new section.
> virtual AtomSection<ELFT> *createSection(
> StringRef name, int32_t contentType,
> DefinedAtom::ContentPermissions contentPermissions,
> SectionOrder sectionOrder);
>
> +private:
> + /// Helper function that returns the priority value from an input
> section.
> + uint32_t getPriorityFromSectionName(StringRef sectionName) const;
> +
> protected:
> llvm::BumpPtrAllocator _allocator;
> SectionMapT _sectionMap;
> @@ -657,13 +669,56 @@ template <class ELFT> void DefaultLayout
> }
> }
>
> +template <class ELFT>
> +uint32_t
> +DefaultLayout<ELFT>::getPriorityFromSectionName(StringRef sectionName)
> const {
> + StringRef priority = sectionName.drop_front().rsplit('.').second;
> + uint32_t prio;
> + if (priority.getAsInteger(10, prio))
> + return std::numeric_limits<uint32_t>::max();
> + return prio;
> +}
> +
> +template <class ELFT>
> +void DefaultLayout<ELFT>::sortOutputSectionByPriority(
> + StringRef outputSectionName, StringRef prefix) {
> + OutputSection<ELFT> *outputSection =
> findOutputSection(outputSectionName);
> + if (!outputSection)
> + return;
> +
> + auto sections = outputSection->sections();
> +
> + std::sort(sections.begin(), sections.end(),
> + [&](Chunk<ELFT> *lhs, Chunk<ELFT> *rhs) {
> + Section<ELFT> *lhsSection = dyn_cast<Section<ELFT>>(lhs);
> + Section<ELFT> *rhsSection = dyn_cast<Section<ELFT>>(rhs);
> + if (!lhsSection || !rhsSection)
> + return false;
> + StringRef lhsSectionName = lhsSection->inputSectionName();
> + StringRef rhsSectionName = rhsSection->inputSectionName();
> +
> + if (!prefix.empty()) {
> + if (!lhsSectionName.startswith(prefix) ||
> + !rhsSectionName.startswith(prefix))
> + return false;
> + }
+ return getPriorityFromSectionName(lhsSectionName) <
> + getPriorityFromSectionName(rhsSectionName);
> + });
>
This sort does not preserve the original section order if they don't start
with a given prefix.
+};
> +
> template <class ELFT> void
> DefaultLayout<ELFT>::assignSectionsToSegments() {
> ScopedTask task(getDefaultDomain(), "assignSectionsToSegments");
> ELFLinkingContext::OutputMagic outputMagic = _context.getOutputMagic();
> // sort the sections by their order as defined by the layout
> sortInputSections();
> +
> // Create output sections.
> createOutputSections();
> +
> + // Finalize output section layout.
> + finalizeOutputSectionLayout();
> +
> // Set the ordinal after sorting the sections
> int ordinal = 1;
> for (auto osi : _outputSections) {
>
> Modified: lld/trunk/lib/ReaderWriter/ELF/OrderPass.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/OrderPass.h?rev=232866&r1=232865&r2=232866&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/ELF/OrderPass.h (original)
> +++ lld/trunk/lib/ReaderWriter/ELF/OrderPass.h Fri Mar 20 18:47:03 2015
> @@ -17,49 +17,13 @@ namespace lld {
> namespace elf {
>
> /// \brief This pass sorts atoms by file and atom ordinals.
> -/// .{init,fini}_array.<priority> sections are handled specially.
> class OrderPass : public Pass {
> public:
> void perform(std::unique_ptr<MutableFile> &file) override {
> - MutableFile::DefinedAtomRange defined = file->definedAtoms();
> - auto last = std::partition(defined.begin(), defined.end(),
> isInitFini);
> - parallel_sort(defined.begin(), last, compareInitFini);
> - parallel_sort(last, defined.end(), DefinedAtom::compareByPosition);
> - }
> -
> -private:
> - static bool isInitFini(const DefinedAtom *atom) {
> - if (atom->sectionChoice() != DefinedAtom::sectionCustomRequired)
> - return false;
> - StringRef name = atom->customSectionName();
> - return name.startswith(".init_array") ||
> name.startswith(".fini_array");
> - }
> -
> - // Parses the number in .{init,fini}_array.<number>.
> - // Returns UINT32_MAX by default.
> - static uint32_t getPriority(const DefinedAtom *atom) {
> - StringRef sec = atom->customSectionName();
> - StringRef num = sec.drop_front().rsplit('.').second;
> - uint32_t prio;
> - if (num.getAsInteger(10, prio))
> - return std::numeric_limits<uint32_t>::max();
> - return prio;
> - }
> -
> - static bool compareInitFini(const DefinedAtom *lhs, const DefinedAtom
> *rhs) {
> - // Sort {.init_array, .fini_array}[.<num>] sections
> - // according to their number. Sections without optional
> - // numer suffix should go last.
> - uint32_t lp = getPriority(lhs);
> - uint32_t rp = getPriority(rhs);
> - if (lp != rp)
> - return lp < rp;
> -
> - // If both atoms have the same priority, fall back to default.
> - return DefinedAtom::compareByPosition(lhs, rhs);
> + parallel_sort(file->definedAtoms().begin(),
> file->definedAtoms().end(),
> + DefinedAtom::compareByPosition);
> }
> };
> -
> }
> }
>
>
> Modified: lld/trunk/lib/ReaderWriter/ELF/X86_64/X86_64TargetHandler.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/X86_64/X86_64TargetHandler.h?rev=232866&r1=232865&r2=232866&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/ELF/X86_64/X86_64TargetHandler.h (original)
> +++ lld/trunk/lib/ReaderWriter/ELF/X86_64/X86_64TargetHandler.h Fri Mar 20
> 18:47:03 2015
> @@ -24,6 +24,11 @@ class X86_64TargetLayout : public Target
> public:
> X86_64TargetLayout(X86_64LinkingContext &context)
> : TargetLayout(context) {}
> +
> + void finalizeOutputSectionLayout() override {
> + sortOutputSectionByPriority(".init_array", ".init_array");
> + sortOutputSectionByPriority(".fini_array", ".fini_array");
>
And you call the function twice. The result of the first invocation would
be invalidated by the second invocation.
> + }
> };
>
> class X86_64TargetHandler
>
> Modified: lld/trunk/test/elf/init_array-order.test
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf/init_array-order.test?rev=232866&r1=232865&r2=232866&view=diff
>
> ==============================================================================
> --- lld/trunk/test/elf/init_array-order.test (original)
> +++ lld/trunk/test/elf/init_array-order.test Fri Mar 20 18:47:03 2015
> @@ -1,6 +1,7 @@
> #RUN: yaml2obj -format=elf %s > %t
> #RUN: lld -flavor gnu -target x86_64-linux %t --noinhibit-exec \
> -#RUN: --output-filetype=yaml | FileCheck %s
> +#RUN: -o %t1.out
> +#RUN: llvm-objdump -s %t1.out | FileCheck %s
>
> !ELF
> FileHeader:
> @@ -62,12 +63,5 @@ Symbols:
> Type: STT_SECTION
> Section: .init_array
>
> -#CHECK: defined-atoms:
> -#CHECK: content: [ 01,
> -#CHECK: section-name: .init_array.1
> -#CHECK: content: [ 02,
> -#CHECK: section-name: .init_array.2
> -#CHECK: content: [ 03,
> -#CHECK: section-name: .init_array.3
> -#CHECK: content: [ 99,
> -#CHECK: section-name: .init_array
> +#CHECK: {{[0xa-f0-9]+}} 01000000 00000000 02000000 00000000
> +#CHECK: {{[0xa-f0-9]+}} 03000000 00000000 99000000 00000000
>
>
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