From 16cfa60cbd8c792228fc9d112c5bcc1b7eb55743 Mon Sep 17 00:00:00 2001 From: Nick Kledzik Date: Wed, 12 Nov 2014 22:21:56 +0000 Subject: [PATCH] [mach-o] Support linker synthesized mach_header symbols. On darwin in final linked images, the __TEXT segment covers that start of the file. That means in memory a process can see the mach_header (and load commands) for every loaded image in a process. There are APIs that take and return the mach_header addresses as a way to specify a particular loaded image. For completeness, any code can get the address of the mach_header of the image it is in by using &__dso_handle. In addition there are mach-o type specific symbols like __mh_execute_header. The linker needs to supply a definition for any of these symbols if used. But the address the symbol it resolves to is not in any section. Instead it is the address of the start of the __TEXT segment. I needed to make a small change to SimpleFileNode to not override resetNextIndex() because the Driver creates a SimpleFileNode to hold the internal/implicit files that the context/writer can create. For some reason SimpleFileNode overrode resetNextIndex() to do nothing instead of reseting the index (which mach-o needs if the internal file is an archive). llvm-svn: 221822 --- lld/include/lld/Core/DefinedAtom.h | 1 + lld/include/lld/Core/InputGraph.h | 3 - lld/lib/Core/DefinedAtom.cpp | 1 + lld/lib/ReaderWriter/MachO/ExecutableAtoms.hpp | 70 ++++++++++++++++++++++ .../MachO/MachONormalizedFileFromAtoms.cpp | 14 ++++- lld/lib/ReaderWriter/MachO/WriterMachO.cpp | 3 + lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp | 1 + lld/test/mach-o/dso_handle.yaml | 62 +++++++++++++++++++ lld/test/mach-o/mh_bundle_header.yaml | 53 ++++++++++++++++ lld/test/mach-o/mh_dylib_header.yaml | 53 ++++++++++++++++ 10 files changed, 257 insertions(+), 4 deletions(-) create mode 100644 lld/test/mach-o/dso_handle.yaml create mode 100644 lld/test/mach-o/mh_bundle_header.yaml create mode 100644 lld/test/mach-o/mh_dylib_header.yaml diff --git a/lld/include/lld/Core/DefinedAtom.h b/lld/include/lld/Core/DefinedAtom.h index 38e58382..cc3b9e6 100644 --- a/lld/include/lld/Core/DefinedAtom.h +++ b/lld/include/lld/Core/DefinedAtom.h @@ -143,6 +143,7 @@ public: 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] diff --git a/lld/include/lld/Core/InputGraph.h b/lld/include/lld/Core/InputGraph.h index ef408f0..f72a212 100644 --- a/lld/include/lld/Core/InputGraph.h +++ b/lld/include/lld/Core/InputGraph.h @@ -296,9 +296,6 @@ public: return make_error_code(InputGraphError::no_more_files); return *_files[_nextFileIndex++]; } - - // Do nothing here. - void resetNextIndex() override {} }; } // namespace lld diff --git a/lld/lib/Core/DefinedAtom.cpp b/lld/lib/Core/DefinedAtom.cpp index fa2fa45..298a768 100644 --- a/lld/lib/Core/DefinedAtom.cpp +++ b/lld/lib/Core/DefinedAtom.cpp @@ -28,6 +28,7 @@ DefinedAtom::ContentPermissions DefinedAtom::permissions(ContentType type) { case typeBranchShim: case typeStub: case typeStubHelper: + case typeMachHeader: return permR_X; case typeConstant: diff --git a/lld/lib/ReaderWriter/MachO/ExecutableAtoms.hpp b/lld/lib/ReaderWriter/MachO/ExecutableAtoms.hpp index f0788fa3..693a428 100644 --- a/lld/lib/ReaderWriter/MachO/ExecutableAtoms.hpp +++ b/lld/lib/ReaderWriter/MachO/ExecutableAtoms.hpp @@ -10,8 +10,11 @@ #ifndef LLD_READER_WRITER_MACHO_EXECUTABLE_ATOMS_H #define LLD_READER_WRITER_MACHO_EXECUTABLE_ATOMS_H +#include "Atoms.h" + #include "llvm/Support/MachO.h" +#include "lld/Core/ArchiveLibraryFile.h" #include "lld/Core/DefinedAtom.h" #include "lld/Core/File.h" #include "lld/Core/LinkingContext.h" @@ -58,8 +61,75 @@ private: }; +// +// MachHeaderAliasFile lazily instantiates the magic symbols that mark the start +// of the mach_header for final linked images. +// +class MachHeaderAliasFile : public ArchiveLibraryFile { +public: + MachHeaderAliasFile(const MachOLinkingContext &context) + : ArchiveLibraryFile("mach_header symbols") { + switch (context.outputMachOType()) { + case llvm::MachO::MH_EXECUTE: + _machHeaderSymbolName = "__mh_execute_header"; + break; + case llvm::MachO::MH_DYLIB: + _machHeaderSymbolName = "__mh_dylib_header"; + break; + case llvm::MachO::MH_BUNDLE: + _machHeaderSymbolName = "__mh_bundle_header"; + break; + case llvm::MachO::MH_DYLINKER: + _machHeaderSymbolName = "__mh_dylinker_header"; + break; + case llvm::MachO::MH_PRELOAD: + _machHeaderSymbolName = "__mh_preload_header"; + break; + default: + llvm_unreachable("no mach_header symbol for file type"); + } + } + + std::error_code + parseAllMembers(std::vector> &result) const override { + return std::error_code(); + } + + const File *find(StringRef sym, bool dataSymbolOnly) const override { + if (sym.equals("___dso_handle") || sym.equals(_machHeaderSymbolName)) { + _definedAtoms._atoms.push_back(new (_alloc) MachODefinedAtom( + *this, sym, DefinedAtom::scopeLinkageUnit, + DefinedAtom::typeMachHeader, DefinedAtom::mergeNo, false, false, + ArrayRef())); + return this; + } + return nullptr; + } + + const atom_collection &defined() const override { + return _definedAtoms; + } + const atom_collection &undefined() const override { + return _undefinedAtoms; + } + const atom_collection &sharedLibrary() const override { + return _sharedLibraryAtoms; + } + const atom_collection &absolute() const override { + return _absoluteAtoms; + } + + +private: + mutable atom_collection_vector _definedAtoms; + atom_collection_vector _undefinedAtoms; + atom_collection_vector _sharedLibraryAtoms; + atom_collection_vector _absoluteAtoms; + StringRef _machHeaderSymbolName; + mutable llvm::BumpPtrAllocator _alloc; +}; } // namespace mach_o } // namespace lld diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp index 8333d09..780c9c0 100644 --- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp +++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp @@ -167,6 +167,7 @@ private: DylibPathToInfo _dylibInfo; const DefinedAtom *_entryAtom; AtomToIndex _atomToSymbolIndex; + std::vector _machHeaderAliasAtoms; }; @@ -331,7 +332,10 @@ void Util::appendAtom(SectionInfo *sect, const DefinedAtom *atom) { void Util::assignAtomsToSections(const lld::File &atomFile) { for (const DefinedAtom *atom : atomFile.defined()) { - appendAtom(sectionForAtom(atom), atom); + if (atom->contentType() == DefinedAtom::typeMachHeader) + _machHeaderAliasAtoms.push_back(atom); + else + appendAtom(sectionForAtom(atom), atom); } } @@ -653,6 +657,14 @@ void Util::buildAtomToAddressMap() { << " name=" << info.atom->name() << "\n"); } } + for (const Atom *atom : _machHeaderAliasAtoms) { + _atomToAddress[atom] = _context.baseAddress(); + DEBUG_WITH_TYPE("WriterMachO-address", llvm::dbgs() + << " address=" + << llvm::format("0x%016X", _atomToAddress[atom]) + << " atom=" << atom + << " name=" << atom->name() << "\n"); + } } uint16_t Util::descBits(const DefinedAtom* atom) { diff --git a/lld/lib/ReaderWriter/MachO/WriterMachO.cpp b/lld/lib/ReaderWriter/MachO/WriterMachO.cpp index 17102df..a0e9d43 100644 --- a/lld/lib/ReaderWriter/MachO/WriterMachO.cpp +++ b/lld/lib/ReaderWriter/MachO/WriterMachO.cpp @@ -52,6 +52,9 @@ public: // If this can link with dylibs, need helper function (dyld_stub_binder). if (_context.needsStubsPass()) r.emplace_back(new StubHelperFile(_context)); + // Final linked images can access a symbol for their mach_header. + if (_context.outputMachOType() != llvm::MachO::MH_OBJECT) + r.emplace_back(new MachHeaderAliasFile(_context)); return true; } diff --git a/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp b/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp index 72537b9..6993ee4 100644 --- a/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp +++ b/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp @@ -447,6 +447,7 @@ template <> struct ScalarEnumerationTraits { io.enumCase(value, "tlv-zero-fill", DefinedAtom::typeTLVInitialZeroFill); io.enumCase(value, "tlv-initializer-ptr", DefinedAtom::typeTLVInitializerPtr); + io.enumCase(value, "mach_header", DefinedAtom::typeMachHeader); io.enumCase(value, "thread-data", DefinedAtom::typeThreadData); io.enumCase(value, "thread-zero-fill",DefinedAtom::typeThreadZeroFill); io.enumCase(value, "ro-note", DefinedAtom::typeRONote); diff --git a/lld/test/mach-o/dso_handle.yaml b/lld/test/mach-o/dso_handle.yaml new file mode 100644 index 0000000..d39d2c2 --- /dev/null +++ b/lld/test/mach-o/dso_handle.yaml @@ -0,0 +1,62 @@ +# RUN: lld -flavor darwin -arch x86_64 %s %p/Inputs/libSystem.yaml -o %t1 +# RUN: llvm-nm -m -n %t1 | FileCheck %s +# +# RUN: lld -flavor darwin -arch x86_64 %s %p/Inputs/libSystem.yaml -dead_strip -o %t2 +# RUN: llvm-nm -m -n %t2 | FileCheck %s +# +# RUN: lld -flavor darwin -arch x86_64 %s %p/Inputs/libSystem.yaml -dylib -o %t3 +# RUN: llvm-nm -m -n %t3 | FileCheck %s +# +# RUN: lld -flavor darwin -arch x86_64 %s %p/Inputs/libSystem.yaml -bundle -o %t4 +# RUN: llvm-nm -m -n %t4 | FileCheck %s +# +# Test that ___dso_handle symbol is available for executables, bundles, and dylibs +# + +--- !mach-o +arch: x86_64 +file-type: MH_OBJECT +flags: [ MH_SUBSECTIONS_VIA_SYMBOLS ] +sections: + - segment: __TEXT + section: __text + type: S_REGULAR + attributes: [ S_ATTR_PURE_INSTRUCTIONS, S_ATTR_SOME_INSTRUCTIONS ] + address: 0x0000000000000000 + content: [ 0x55, 0x48, 0x89, 0xE5, 0x31, 0xC0, 0x5D, 0xC3 ] + - segment: __DATA + section: __data + type: S_REGULAR + attributes: [ ] + alignment: 3 + address: 0x0000000000000008 + content: [ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ] + relocations: + - offset: 0x00000000 + type: X86_64_RELOC_UNSIGNED + length: 3 + pc-rel: false + extern: true + symbol: 2 +global-symbols: + - name: _d + type: N_SECT + scope: [ N_EXT ] + sect: 2 + value: 0x0000000000000008 + - name: _main + type: N_SECT + scope: [ N_EXT ] + sect: 1 + value: 0x0000000000000000 +undefined-symbols: + - name: ___dso_handle + type: N_UNDF + scope: [ N_EXT ] + value: 0x0000000000000000 + + +... + +# CHECK_NOT: ___dso_handle +# CHECK: _main diff --git a/lld/test/mach-o/mh_bundle_header.yaml b/lld/test/mach-o/mh_bundle_header.yaml new file mode 100644 index 0000000..558df2c --- /dev/null +++ b/lld/test/mach-o/mh_bundle_header.yaml @@ -0,0 +1,53 @@ +# RUN: lld -flavor darwin -arch x86_64 %s -bundle -o %t %p/Inputs/libSystem.yaml +# RUN: llvm-nm -m -n %t | FileCheck %s +# +# Test that __mh_bundle_header symbol is available for bundles +# + +--- !mach-o +arch: x86_64 +file-type: MH_OBJECT +flags: [ MH_SUBSECTIONS_VIA_SYMBOLS ] +sections: + - segment: __TEXT + section: __text + type: S_REGULAR + attributes: [ S_ATTR_PURE_INSTRUCTIONS, S_ATTR_SOME_INSTRUCTIONS ] + address: 0x0000000000000000 + content: [ 0x55, 0x48, 0x89, 0xE5, 0x31, 0xC0, 0x5D, 0xC3 ] + - segment: __DATA + section: __data + type: S_REGULAR + attributes: [ ] + alignment: 3 + address: 0x0000000000000008 + content: [ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ] + relocations: + - offset: 0x00000000 + type: X86_64_RELOC_UNSIGNED + length: 3 + pc-rel: false + extern: true + symbol: 2 +global-symbols: + - name: _d + type: N_SECT + scope: [ N_EXT ] + sect: 2 + value: 0x0000000000000008 + - name: _foo + type: N_SECT + scope: [ N_EXT ] + sect: 1 + value: 0x0000000000000000 +undefined-symbols: + - name: __mh_bundle_header + type: N_UNDF + scope: [ N_EXT ] + value: 0x0000000000000000 + + +... + +# CHECK_NOT: __mh_bundle_header +# CHECK: _foo diff --git a/lld/test/mach-o/mh_dylib_header.yaml b/lld/test/mach-o/mh_dylib_header.yaml new file mode 100644 index 0000000..07429b3 --- /dev/null +++ b/lld/test/mach-o/mh_dylib_header.yaml @@ -0,0 +1,53 @@ +# RUN: lld -flavor darwin -arch x86_64 %s -dylib -o %t %p/Inputs/libSystem.yaml +# RUN: llvm-nm -m -n %t | FileCheck %s +# +# Test that __mh_dylib_header symbol is available for dylibs +# + +--- !mach-o +arch: x86_64 +file-type: MH_OBJECT +flags: [ MH_SUBSECTIONS_VIA_SYMBOLS ] +sections: + - segment: __TEXT + section: __text + type: S_REGULAR + attributes: [ S_ATTR_PURE_INSTRUCTIONS, S_ATTR_SOME_INSTRUCTIONS ] + address: 0x0000000000000000 + content: [ 0x55, 0x48, 0x89, 0xE5, 0x31, 0xC0, 0x5D, 0xC3 ] + - segment: __DATA + section: __data + type: S_REGULAR + attributes: [ ] + alignment: 3 + address: 0x0000000000000008 + content: [ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ] + relocations: + - offset: 0x00000000 + type: X86_64_RELOC_UNSIGNED + length: 3 + pc-rel: false + extern: true + symbol: 2 +global-symbols: + - name: _d + type: N_SECT + scope: [ N_EXT ] + sect: 2 + value: 0x0000000000000008 + - name: _foo + type: N_SECT + scope: [ N_EXT ] + sect: 1 + value: 0x0000000000000000 +undefined-symbols: + - name: __mh_dylib_header + type: N_UNDF + scope: [ N_EXT ] + value: 0x0000000000000000 + + +... + +# CHECK_NOT: __mh_dylib_header +# CHECK: _foo -- 2.7.4