c0c464cac1
In trying to fix the leaks in the MachO lld codebase, we need to have a better model for file and atom ownership. Having the context own everything seems like the simplest model, so change all the passes to allocate File's on the context instead of owning files as a member. llvm-svn: 264004
130 lines
4.5 KiB
C++
130 lines
4.5 KiB
C++
//===- lib/ReaderWriter/MachO/ShimPass.cpp -------------------------------===//
|
|
//
|
|
// The LLVM Linker
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This linker pass updates branch-sites whose target is a different mode
|
|
// (thumb vs arm).
|
|
//
|
|
// Arm code has two instruction encodings thumb and arm. When branching from
|
|
// one code encoding to another, you need to use an instruction that switches
|
|
// the instruction mode. Usually the transition only happens at call sites, and
|
|
// the linker can transform a BL instruction in BLX (or vice versa). But if the
|
|
// compiler did a tail call optimization and a function ends with a branch (not
|
|
// branch and link), there is no pc-rel BX instruction.
|
|
//
|
|
// The ShimPass looks for pc-rel B instructions that will need to switch mode.
|
|
// For those cases it synthesizes a shim which does the transition, then
|
|
// modifies the original atom with the B instruction to target to the shim atom.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "ArchHandler.h"
|
|
#include "File.h"
|
|
#include "MachOPasses.h"
|
|
#include "lld/Core/DefinedAtom.h"
|
|
#include "lld/Core/File.h"
|
|
#include "lld/Core/LLVM.h"
|
|
#include "lld/Core/Reference.h"
|
|
#include "lld/Core/Simple.h"
|
|
#include "lld/ReaderWriter/MachOLinkingContext.h"
|
|
#include "llvm/ADT/DenseMap.h"
|
|
#include "llvm/ADT/STLExtras.h"
|
|
|
|
namespace lld {
|
|
namespace mach_o {
|
|
|
|
class ShimPass : public Pass {
|
|
public:
|
|
ShimPass(const MachOLinkingContext &context)
|
|
: _ctx(context), _archHandler(_ctx.archHandler()),
|
|
_stubInfo(_archHandler.stubInfo()),
|
|
_file(*_ctx.make_file<MachOFile>("<mach-o shim pass>")) {
|
|
_file.setOrdinal(_ctx.getNextOrdinalAndIncrement());
|
|
}
|
|
|
|
std::error_code perform(SimpleFile &mergedFile) override {
|
|
// Scan all references in all atoms.
|
|
for (const DefinedAtom *atom : mergedFile.defined()) {
|
|
for (const Reference *ref : *atom) {
|
|
// Look at non-call branches.
|
|
if (!_archHandler.isNonCallBranch(*ref))
|
|
continue;
|
|
const Atom *target = ref->target();
|
|
assert(target != nullptr);
|
|
if (const lld::DefinedAtom *daTarget = dyn_cast<DefinedAtom>(target)) {
|
|
bool atomIsThumb = _archHandler.isThumbFunction(*atom);
|
|
bool targetIsThumb = _archHandler.isThumbFunction(*daTarget);
|
|
if (atomIsThumb != targetIsThumb)
|
|
updateBranchToUseShim(atomIsThumb, *daTarget, ref);
|
|
}
|
|
}
|
|
}
|
|
// Exit early if no shims needed.
|
|
if (_targetToShim.empty())
|
|
return std::error_code();
|
|
|
|
// Sort shim atoms so the layout order is stable.
|
|
std::vector<const DefinedAtom *> shims;
|
|
shims.reserve(_targetToShim.size());
|
|
for (auto element : _targetToShim) {
|
|
shims.push_back(element.second);
|
|
}
|
|
std::sort(shims.begin(), shims.end(),
|
|
[](const DefinedAtom *l, const DefinedAtom *r) {
|
|
return (l->name() < r->name());
|
|
});
|
|
|
|
// Add all shims to master file.
|
|
for (const DefinedAtom *shim : shims)
|
|
mergedFile.addAtom(*shim);
|
|
|
|
return std::error_code();
|
|
}
|
|
|
|
private:
|
|
|
|
void updateBranchToUseShim(bool thumbToArm, const DefinedAtom& target,
|
|
const Reference *ref) {
|
|
// Make file-format specific stub and other support atoms.
|
|
const DefinedAtom *shim = this->getShim(thumbToArm, target);
|
|
assert(shim != nullptr);
|
|
// Switch branch site to target shim atom.
|
|
const_cast<Reference *>(ref)->setTarget(shim);
|
|
}
|
|
|
|
const DefinedAtom* getShim(bool thumbToArm, const DefinedAtom& target) {
|
|
auto pos = _targetToShim.find(&target);
|
|
if ( pos != _targetToShim.end() ) {
|
|
// Reuse an existing shim.
|
|
assert(pos->second != nullptr);
|
|
return pos->second;
|
|
} else {
|
|
// There is no existing shim, so create a new one.
|
|
const DefinedAtom *shim = _archHandler.createShim(_file, thumbToArm,
|
|
target);
|
|
_targetToShim[&target] = shim;
|
|
return shim;
|
|
}
|
|
}
|
|
|
|
const MachOLinkingContext &_ctx;
|
|
mach_o::ArchHandler &_archHandler;
|
|
const ArchHandler::StubInfo &_stubInfo;
|
|
MachOFile &_file;
|
|
llvm::DenseMap<const Atom*, const DefinedAtom*> _targetToShim;
|
|
};
|
|
|
|
|
|
|
|
void addShimPass(PassManager &pm, const MachOLinkingContext &ctx) {
|
|
pm.add(llvm::make_unique<ShimPass>(ctx));
|
|
}
|
|
|
|
} // end namespace mach_o
|
|
} // end namespace lld
|