// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////

//

/// \file       arm64.c

/// \brief      Filter for ARM64 binaries

///

/// This converts ARM64 relative addresses in the BL and ADRP immediates

/// to absolute values to increase redundancy of ARM64 code.

///

/// Converting B or ADR instructions was also tested but it's not useful.

/// A majority of the jumps for the B instruction are very small (+/- 0xFF).

/// These are typical for loops and if-statements. Encoding them to their

/// absolute address reduces redundancy since many of the small relative

/// jump values are repeated, but very few of the absolute addresses are.

//

//  Authors:    Lasse Collin

//              Jia Tan

//              Igor Pavlov

//

///////////////////////////////////////////////////////////////////////////////

#include "simple_private.h"

static size_t

arm64_code(void *simple lzma_attribute((__unused__)),

    uint32_t now_pos, bool is_encoder,

    uint8_t *buffer, size_t size)

{

  size_t i;

  // Clang 14.0.6 on x86-64 makes this four times bigger and 40 % slower

  // with auto-vectorization that is enabled by default with -O2.

  // Such vectorization bloat happens with -O2 when targeting ARM64 too

  // but performance hasn't been tested.

#ifdef __clang__

# pragma clang loop vectorize(disable)

#endif

  for (i = 0; i + 4 <= size; i += 4) {

    uint32_t pc = (uint32_t)(now_pos + i);

    uint32_t instr = read32le(buffer + i);

    if ((instr >> 26) == 0x25) {

      // BL instruction:

      // The full 26-bit immediate is converted.

      // The range is +/-128 MiB.

      //

      // Using the full range helps quite a lot with

      // big executables. Smaller range would reduce false

      // positives in non-code sections of the input though

      // so this is a compromise that slightly favors big

      // files. With the full range, only six bits of the 32

      // need to match to trigger a conversion.

      const uint32_t src = instr;

      instr = 0x94000000;

      pc >>= 2;

      if (!is_encoder)

        pc = 0U - pc;

      instr |= (src + pc) & 0x03FFFFFF;

      write32le(buffer + i, instr);

    } else if ((instr & 0x9F000000) == 0x90000000) {

      // ADRP instruction:

      // Only values in the range +/-512 MiB are converted.

      //

      // Using less than the full +/-4 GiB range reduces

      // false positives on non-code sections of the input

      // while being excellent for executables up to 512 MiB.

      // The positive effect of ADRP conversion is smaller

      // than that of BL but it also doesn't hurt so much in

      // non-code sections of input because, with +/-512 MiB

      // range, nine bits of 32 need to match to trigger a

      // conversion (two 10-bit match choices = 9 bits).

      const uint32_t src = ((instr >> 29) & 3)

          | ((instr >> 3) & 0x001FFFFC);

      // With the addition only one branch is needed to

      // check the +/- range. This is usually false when

      // processing ARM64 code so branch prediction will

      // handle it well in terms of performance.

      //

      //if ((src & 0x001E0000) != 0

      // && (src & 0x001E0000) != 0x001E0000)

      if ((src + 0x00020000) & 0x001C0000)

        continue;

      instr &= 0x9000001F;

      pc >>= 12;

      if (!is_encoder)

        pc = 0U - pc;

      const uint32_t dest = src + pc;

      instr |= (dest & 3) << 29;

      instr |= (dest & 0x0003FFFC) << 3;

      instr |= (0U - (dest & 0x00020000)) & 0x00E00000;

      write32le(buffer + i, instr);

    }

  }

  return i;

}

static lzma_ret

arm64_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,

    const lzma_filter_info *filters, bool is_encoder)

{

  return lzma_simple_coder_init(next, allocator, filters,

      &arm64_code, 0, 4, 4, is_encoder);

}

#ifdef HAVE_ENCODER_ARM64

extern lzma_ret

lzma_simple_arm64_encoder_init(lzma_next_coder *next,

    const lzma_allocator *allocator,

    const lzma_filter_info *filters)

{

  return arm64_coder_init(next, allocator, filters, true);

}

#endif

#ifdef HAVE_DECODER_ARM64

extern lzma_ret

lzma_simple_arm64_decoder_init(lzma_next_coder *next,

    const lzma_allocator *allocator,

    const lzma_filter_info *filters)

{

  return arm64_coder_init(next, allocator, filters, false);

}

#endif