llvm/bolt/include/bolt/Passes/LongJmp.h

//===- bolt/Passes/LongJmp.h ------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef BOLT_PASSES_LONGJMP_H
#define BOLT_PASSES_LONGJMP_H

#include "bolt/Passes/BinaryPasses.h"

namespace llvm {
namespace bolt {

/// LongJmp is veneer-insertion pass originally written for AArch64 that
/// compensates for its short-range branches, typically done during linking. We
/// pull this pass inside BOLT because here we can do a better job at stub
/// inserting by manipulating the CFG, something linkers can't do.
///
/// We iteratively repeat the following until no modification is done: we do a
/// tentative layout with the current function sizes; then we add stubs for
/// branches that we know are out of range or we expand smaller stubs (28-bit)
/// to a large one if necessary (32 or 64).
///
/// This expansion inserts the equivalent of "linker stubs", small
/// blocks of code that load a 64-bit address into a pre-allocated register and
//  then executes an unconditional indirect branch on this register. By using a
/// 64-bit range, we guarantee it can reach any code location.
///
class LongJmpPass : public BinaryFunctionPass { … };
} // namespace bolt
} // namespace llvm

#endif