llvm-capstone/lld/ELF/ARMErrataFix.h
Peter Smith ea99ce5e9b [ELF][ARM] Implement --fix-cortex-a8 to fix erratum 657417
The --fix-cortex-a8 option implements a linker workaround for the
coretex-a8 erratum 657417. A summary of the erratum conditions is:
- A 32-bit Thumb-2 branch instruction B.w, Bcc.w, BL, BLX spans two
4KiB regions.
- The destination of the branch is to the first 4KiB region.
- The instruction before the branch is a 32-bit Thumb-2 non-branch
instruction.

The linker fix is to redirect the branch to a patch not in the first
4KiB region. The patch forwards the branch on to its target.

The cortex-a8, is an old CPU, with the first implementation of this
workaround in ld.bfd appearing in 2009. The cortex-a8 has been used in
early Android Phones and there are some critical applications that still
need to run on a cortex-a8 that have the erratum. The patch is applied
roughly 10 times on LLD and 20 on Clang when they are built with
--fix-cortex-a8 on an Arm system.

The formal erratum description is avaliable in the ARM Core Cortex-A8
(AT400/AT401) Errata Notice document. This is available from Arm on
request but it seems to be findable via a web search.

Differential Revision: https://reviews.llvm.org/D67284

llvm-svn: 371965
2019-09-16 09:38:38 +00:00

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//===- ARMErrataFix.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 LLD_ELF_ARMA8ERRATAFIX_H
#define LLD_ELF_ARMA8ERRATAFIX_H
#include "lld/Common/LLVM.h"
#include "llvm/ADT/DenseMap.h"
#include <map>
#include <vector>
namespace lld {
namespace elf {
class Defined;
class InputSection;
struct InputSectionDescription;
class OutputSection;
class Patch657417Section;
class ARMErr657417Patcher {
public:
// Return true if Patches have been added to the OutputSections.
bool createFixes();
private:
std::vector<Patch657417Section *>
patchInputSectionDescription(InputSectionDescription &isd);
void insertPatches(InputSectionDescription &isd,
std::vector<Patch657417Section *> &patches);
void init();
// A cache of the mapping symbols defined by the InputSection sorted in order
// of ascending value with redundant symbols removed. These describe
// the ranges of code and data in an executable InputSection.
llvm::DenseMap<InputSection *, std::vector<const Defined *>> sectionMap;
bool initialized = false;
};
} // namespace elf
} // namespace lld
#endif