diff options
Diffstat (limited to 'include/lld/Core/DefinedAtom.h')
| -rw-r--r-- | include/lld/Core/DefinedAtom.h | 368 |
1 files changed, 368 insertions, 0 deletions
diff --git a/include/lld/Core/DefinedAtom.h b/include/lld/Core/DefinedAtom.h new file mode 100644 index 000000000000..86d880c659b4 --- /dev/null +++ b/include/lld/Core/DefinedAtom.h @@ -0,0 +1,368 @@ +//===- Core/DefinedAtom.h - An Atom with content --------------------------===// +// +// The LLVM Linker +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +#ifndef LLD_CORE_DEFINED_ATOM_H +#define LLD_CORE_DEFINED_ATOM_H + +#include "lld/Core/Atom.h" +#include "lld/Core/LLVM.h" + +namespace lld { +class File; +class Reference; + +/// \brief The fundamental unit of linking. +/// +/// A C function or global variable is an atom. An atom has content and +/// attributes. The content of a function atom is the instructions that +/// implement the function. The content of a global variable atom is its +/// initial bytes. +/// +/// Here are some example attribute sets for common atoms. If a particular +/// attribute is not listed, the default values are: definition=regular, +/// sectionChoice=basedOnContent, scope=translationUnit, merge=no, +/// deadStrip=normal, interposable=no +/// +/// C function: void foo() {} <br> +/// name=foo, type=code, perm=r_x, scope=global +/// +/// C static function: staic void func() {} <br> +/// name=func, type=code, perm=r_x +/// +/// C global variable: int count = 1; <br> +/// name=count, type=data, perm=rw_, scope=global +/// +/// C tentative definition: int bar; <br> +/// name=bar, type=zerofill, perm=rw_, scope=global, +/// merge=asTentative, interposable=yesAndRuntimeWeak +/// +/// Uninitialized C static variable: static int stuff; <br> +/// name=stuff, type=zerofill, perm=rw_ +/// +/// Weak C function: __attribute__((weak)) void foo() {} <br> +/// name=foo, type=code, perm=r_x, scope=global, merge=asWeak +/// +/// Hidden C function: __attribute__((visibility("hidden"))) void foo() {}<br> +/// name=foo, type=code, perm=r_x, scope=linkageUnit +/// +/// No-dead-strip function: __attribute__((used)) void foo() {} <br> +/// name=foo, type=code, perm=r_x, scope=global, deadStrip=never +/// +/// Non-inlined C++ inline method: inline void Foo::doit() {} <br> +/// name=_ZN3Foo4doitEv, type=code, perm=r_x, scope=global, +/// mergeDupes=asWeak +/// +/// Non-inlined C++ inline method whose address is taken: +/// inline void Foo::doit() {} <br> +/// name=_ZN3Foo4doitEv, type=code, perm=r_x, scope=global, +/// mergeDupes=asAddressedWeak +/// +/// literal c-string: "hello" <br> +/// name="" type=cstring, perm=r__, scope=linkageUnit +/// +/// literal double: 1.234 <br> +/// name="" type=literal8, perm=r__, scope=linkageUnit +/// +/// constant: { 1,2,3 } <br> +/// name="" type=constant, perm=r__, scope=linkageUnit +/// +/// Pointer to initializer function: <br> +/// name="" type=initializer, perm=rw_l, +/// sectionChoice=customRequired +/// +/// C function place in custom section: __attribute__((section("__foo"))) +/// void foo() {} <br> +/// name=foo, type=code, perm=r_x, scope=global, +/// sectionChoice=customRequired, customSectionName=__foo +/// +class DefinedAtom : public Atom { +public: + enum Interposable { + interposeNo, // linker can directly bind uses of this atom + interposeYes, // linker must indirect (through GOT) uses + interposeYesAndRuntimeWeak // must indirect and mark symbol weak in final + // linked image + }; + + enum Merge { + mergeNo, // Another atom with same name is error + mergeAsTentative, // Is ANSI C tentative definition, can be coalesced + mergeAsWeak, // Is C++ inline definition that was not inlined, + // but address was not taken, so atom can be hidden + // by linker + mergeAsWeakAndAddressUsed, // Is C++ definition inline definition whose + // address was taken. + mergeSameNameAndSize, // Another atom with different size is error + mergeByLargestSection, // Choose an atom whose section is the largest. + mergeByContent, // Merge with other constants with same content. + }; + + enum ContentType { + typeUnknown, // for use with definitionUndefined + typeCode, // executable code + typeResolver, // function which returns address of target + typeBranchIsland, // linker created for large binaries + typeBranchShim, // linker created to switch thumb mode + typeStub, // linker created for calling external function + typeStubHelper, // linker created for initial stub binding + typeConstant, // a read-only constant + typeCString, // a zero terminated UTF8 C string + typeUTF16String, // a zero terminated UTF16 string + typeCFI, // a FDE or CIE from dwarf unwind info + typeLSDA, // extra unwinding info + typeLiteral4, // a four-btye read-only constant + typeLiteral8, // an eight-btye read-only constant + typeLiteral16, // a sixteen-btye read-only constant + typeData, // read-write data + typeDataFast, // allow data to be quickly accessed + typeZeroFill, // zero-fill data + typeZeroFillFast, // allow zero-fill data to be quicky accessed + typeConstData, // read-only data after dynamic linker is done + typeObjC1Class, // ObjC1 class [Darwin] + typeLazyPointer, // pointer through which a stub jumps + typeLazyDylibPointer, // pointer through which a stub jumps [Darwin] + typeCFString, // NS/CFString object [Darwin] + typeGOT, // pointer to external symbol + typeInitializerPtr, // pointer to initializer function + typeTerminatorPtr, // pointer to terminator function + typeCStringPtr, // pointer to UTF8 C string [Darwin] + typeObjCClassPtr, // pointer to ObjC class [Darwin] + typeObjC2CategoryList, // pointers to ObjC category [Darwin] + typeDTraceDOF, // runtime data for Dtrace [Darwin] + typeInterposingTuples, // tuples of interposing info for dyld [Darwin] + typeTempLTO, // temporary atom for bitcode reader + typeCompactUnwindInfo, // runtime data for unwinder [Darwin] + typeProcessedUnwindInfo,// compressed compact unwind info [Darwin] + typeThunkTLV, // thunk used to access a TLV [Darwin] + typeTLVInitialData, // initial data for a TLV [Darwin] + typeTLVInitialZeroFill, // TLV initial zero fill data [Darwin] + typeTLVInitializerPtr, // pointer to thread local initializer [Darwin] + typeMachHeader, // atom representing mach_header [Darwin] + typeThreadZeroFill, // Uninitialized thread local data(TBSS) [ELF] + typeThreadData, // Initialized thread local data(TDATA) [ELF] + typeRONote, // Identifies readonly note sections [ELF] + typeRWNote, // Identifies readwrite note sections [ELF] + typeNoAlloc, // Identifies non allocatable sections [ELF] + typeGroupComdat, // Identifies a section group [ELF, COFF] + typeGnuLinkOnce, // Identifies a gnu.linkonce section [ELF] + }; + + // Permission bits for atoms and segments. The order of these values are + // important, because the layout pass may sort atoms by permission if other + // attributes are the same. + enum ContentPermissions { + perm___ = 0, // mapped as unaccessible + permR__ = 8, // mapped read-only + permRW_ = 8 + 2, // mapped readable and writable + permRW_L = 8 + 2 + 1, // initially mapped r/w, then made read-only + // loader writable + permR_X = 8 + 4, // mapped readable and executable + permRWX = 8 + 2 + 4, // mapped readable and writable and executable + permUnknown = 16 // unknown or invalid permissions + }; + + enum SectionChoice { + sectionBasedOnContent, // linker infers final section based on content + sectionCustomPreferred, // linker may place in specific section + sectionCustomRequired // linker must place in specific section + }; + + enum DeadStripKind { + deadStripNormal, // linker may dead strip this atom + deadStripNever, // linker must never dead strip this atom + deadStripAlways // linker must remove this atom if unused + }; + + enum DynamicExport { + /// \brief The linker may or may not export this atom dynamically depending + /// on the output type and other context of the link. + dynamicExportNormal, + /// \brief The linker will always export this atom dynamically. + dynamicExportAlways, + }; + + // Attributes describe a code model used by the atom. + enum CodeModel { + codeNA, // no specific code model + codeMipsPIC, // PIC function in a PIC / non-PIC mixed file + codeMipsMicro, // microMIPS instruction encoding + codeMipsMicroPIC, // microMIPS instruction encoding + PIC + codeMips16, // MIPS-16 instruction encoding + codeARMThumb, // ARM Thumb instruction set + }; + + struct Alignment { + Alignment(int p2, int m = 0) + : powerOf2(p2) + , modulus(m) {} + + uint16_t powerOf2; + uint16_t modulus; + + bool operator==(const Alignment &rhs) const { + return (powerOf2 == rhs.powerOf2) && (modulus == rhs.modulus); + } + }; + + /// \brief returns a value for the order of this Atom within its file. + /// + /// This is used by the linker to order the layout of Atoms so that the + /// resulting image is stable and reproducible. + /// + /// Note that this should not be confused with ordinals of exported symbols in + /// Windows DLLs. In Windows terminology, ordinals are symbols' export table + /// indices (small integers) which can be used instead of symbol names to + /// refer items in a DLL. + virtual uint64_t ordinal() const = 0; + + /// \brief the number of bytes of space this atom's content will occupy in the + /// final linked image. + /// + /// For a function atom, it is the number of bytes of code in the function. + virtual uint64_t size() const = 0; + + /// \brief The size of the section from which the atom is instantiated. + /// + /// Merge::mergeByLargestSection is defined in terms of section size + /// and not in terms of atom size, so we need this function separate + /// from size(). + virtual uint64_t sectionSize() const { return 0; } + + /// \brief The visibility of this atom to other atoms. + /// + /// C static functions have scope scopeTranslationUnit. Regular C functions + /// have scope scopeGlobal. Functions compiled with visibility=hidden have + /// scope scopeLinkageUnit so they can be see by other atoms being linked but + /// not by the OS loader. + virtual Scope scope() const = 0; + + /// \brief Whether the linker should use direct or indirect access to this + /// atom. + virtual Interposable interposable() const = 0; + + /// \brief how the linker should handle if multiple atoms have the same name. + virtual Merge merge() const = 0; + + /// \brief The type of this atom, such as code or data. + virtual ContentType contentType() const = 0; + + /// \brief The alignment constraints on how this atom must be laid out in the + /// final linked image (e.g. 16-byte aligned). + virtual Alignment alignment() const = 0; + + /// \brief Whether this atom must be in a specially named section in the final + /// linked image, or if the linker can infer the section based on the + /// contentType(). + virtual SectionChoice sectionChoice() const = 0; + + /// \brief If sectionChoice() != sectionBasedOnContent, then this return the + /// name of the section the atom should be placed into. + virtual StringRef customSectionName() const = 0; + + /// \brief constraints on whether the linker may dead strip away this atom. + virtual DeadStripKind deadStrip() const = 0; + + /// \brief Under which conditions should this atom be dynamically exported. + virtual DynamicExport dynamicExport() const { + return dynamicExportNormal; + } + + /// \brief Code model used by the atom. + virtual CodeModel codeModel() const { return codeNA; } + + /// \brief Returns the OS memory protections required for this atom's content + /// at runtime. + /// + /// A function atom is R_X, a global variable is RW_, and a read-only constant + /// is R__. + virtual ContentPermissions permissions() const; + + /// \brief returns a reference to the raw (unrelocated) bytes of this Atom's + /// content. + virtual ArrayRef<uint8_t> rawContent() const = 0; + + /// This class abstracts iterating over the sequence of References + /// in an Atom. Concrete instances of DefinedAtom must implement + /// the derefIterator() and incrementIterator() methods. + class reference_iterator { + public: + reference_iterator(const DefinedAtom &a, const void *it) + : _atom(a), _it(it) { } + + const Reference *operator*() const { + return _atom.derefIterator(_it); + } + + const Reference *operator->() const { + return _atom.derefIterator(_it); + } + + bool operator!=(const reference_iterator &other) const { + return _it != other._it; + } + + reference_iterator &operator++() { + _atom.incrementIterator(_it); + return *this; + } + private: + const DefinedAtom &_atom; + const void *_it; + }; + + /// \brief Returns an iterator to the beginning of this Atom's References. + virtual reference_iterator begin() const = 0; + + /// \brief Returns an iterator to the end of this Atom's References. + virtual reference_iterator end() const = 0; + + static bool classof(const Atom *a) { + return a->definition() == definitionRegular; + } + + /// Utility for deriving permissions from content type + static ContentPermissions permissions(ContentType type); + + /// Utility function to check if the atom occupies file space + bool occupiesDiskSpace() const { + ContentType atomContentType = contentType(); + return !(atomContentType == DefinedAtom::typeZeroFill || + atomContentType == DefinedAtom::typeZeroFillFast || + atomContentType == DefinedAtom::typeTLVInitialZeroFill || + atomContentType == DefinedAtom::typeThreadZeroFill); + } + + /// Utility function to check if the atom belongs to a group section + /// that represents section groups or .gnu.linkonce sections. + bool isGroupParent() const { + ContentType atomContentType = contentType(); + return (atomContentType == DefinedAtom::typeGroupComdat || + atomContentType == DefinedAtom::typeGnuLinkOnce); + } + + // Returns true if lhs should be placed before rhs in the final output. + static bool compareByPosition(const DefinedAtom *lhs, + const DefinedAtom *rhs); + +protected: + // DefinedAtom is an abstract base class. Only subclasses can access + // constructor. + DefinedAtom() : Atom(definitionRegular) { } + + /// \brief Returns a pointer to the Reference object that the abstract + /// iterator "points" to. + virtual const Reference *derefIterator(const void *iter) const = 0; + + /// \brief Adjusts the abstract iterator to "point" to the next Reference + /// object for this Atom. + virtual void incrementIterator(const void *&iter) const = 0; +}; +} // end namespace lld + +#endif |