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[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
This commit is contained in:
Nick Kledzik 2014-11-12 22:21:56 +00:00
parent 0140aa8756
commit 16cfa60cbd
10 changed files with 257 additions and 4 deletions
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1
lld/include/lld/Core/DefinedAtom.h
View File

@ -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]

3
lld/include/lld/Core/InputGraph.h
View File

@ -296,9 +296,6 @@ public:
return make_error_code(InputGraphError::no_more_files);
return *_files[_nextFileIndex++];
}
// Do nothing here.
void resetNextIndex() override {}
};
} // namespace lld

1
lld/lib/Core/DefinedAtom.cpp
View File

@ -28,6 +28,7 @@ DefinedAtom::ContentPermissions DefinedAtom::permissions(ContentType type) {
case typeBranchShim:
case typeStub:
case typeStubHelper:
case typeMachHeader:
return permR_X;
case typeConstant:

70
lld/lib/ReaderWriter/MachO/ExecutableAtoms.hpp
View File

@ -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<std::unique_ptr<File>> &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<uint8_t>()));
return this;
}
return nullptr;
}
const atom_collection<DefinedAtom> &defined() const override {
return _definedAtoms;
}
const atom_collection<UndefinedAtom> &undefined() const override {
return _undefinedAtoms;
}
const atom_collection<SharedLibraryAtom> &sharedLibrary() const override {
return _sharedLibraryAtoms;
}
const atom_collection<AbsoluteAtom> &absolute() const override {
return _absoluteAtoms;
}
private:
mutable atom_collection_vector<DefinedAtom> _definedAtoms;
atom_collection_vector<UndefinedAtom> _undefinedAtoms;
atom_collection_vector<SharedLibraryAtom> _sharedLibraryAtoms;
atom_collection_vector<AbsoluteAtom> _absoluteAtoms;
StringRef _machHeaderSymbolName;
mutable llvm::BumpPtrAllocator _alloc;
};
} // namespace mach_o
} // namespace lld

14
lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
View File

@ -167,6 +167,7 @@ private:
DylibPathToInfo _dylibInfo;
const DefinedAtom *_entryAtom;
AtomToIndex _atomToSymbolIndex;
std::vector<const Atom *> _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) {

3
lld/lib/ReaderWriter/MachO/WriterMachO.cpp
View File

@ -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;
}

1
lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
View File

@ -447,6 +447,7 @@ template <> struct ScalarEnumerationTraits<lld::DefinedAtom::ContentType> {
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);

62
lld/test/mach-o/dso_handle.yaml Normal file
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@ -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

53
lld/test/mach-o/mh_bundle_header.yaml Normal file
View File

@ -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

53
lld/test/mach-o/mh_dylib_header.yaml Normal file
View File

@ -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