// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "courgette/disassembler_elf_32_arm.h"
#include <algorithm>
#include <string>
#include <vector>
#include "base/basictypes.h"
#include "base/logging.h"
#include "courgette/assembly_program.h"
#include "courgette/courgette.h"
#include "courgette/encoded_program.h"
namespace courgette {
CheckBool DisassemblerElf32ARM::Compress(ARM_RVA type, uint32 arm_op, RVA rva,
uint16* c_op, uint32* addr) {
// This method takes an ARM or thumb opcode, extracts the relative
// target address from it (addr), and creates a corresponding
// Courgette opcode (c_op).
//
// Details on ARM the opcodes, and how the relative targets are
// computed were taken from the "ARM Architecture Reference Manual",
// section A4.1.5 and the "Thumb-2 supplement", section 4.6.12.
// ARM_OFF24 is for the ARM opcode. The rest are for thumb opcodes.
switch (type) {
case ARM_OFF8: {
// The offset is given by lower 8 bits of the op. It is a 9-bit
// offset, shifted right one bit and signed extended.
uint32 temp = (arm_op & 0x00FF) << 1;
if (temp & 0x0100)
temp |= 0xFFFFFE00;
temp += 4; // Offset from _next_ PC.
fflush(stdout);
(*addr) = temp;
(*c_op) = (arm_op >> 8) | 0x1000;
break;
}
case ARM_OFF11: {
// The offset is given by lower 11 bits of the op, and is a
// 12-bit offset, shifted right one bit and sign extended.
uint32 temp = (arm_op & 0x07FF) << 1;
if (temp & 0x00000800)
temp |= 0xFFFFF000;
temp += 4; // Offset from _next_ PC.
(*addr) = temp;
(*c_op) = (arm_op >> 11) | 0x2000;
break;
}
case ARM_OFF24: {
// The offset is given by the lower 24-bits of the op, shifted
// left 2 bits, and sign extended.
uint32 temp = (arm_op & 0x00FFFFFF) << 2;
if (temp & 0x02000000)
temp |= 0xFC000000;
temp += 8;
(*addr) = temp;
(*c_op) = (arm_op >> 24) | 0x3000;
break;
}
case ARM_OFF25: {
uint32 temp = 0;
temp |= (arm_op & 0x000007FF) << 1; // imm11
temp |= (arm_op & 0x03FF0000) >> 4; // imm10
uint32 S = (arm_op & (1 << 26)) >> 26;
uint32 j2 = (arm_op & (1 << 11)) >> 11;
uint32 j1 = (arm_op & (1 << 13)) >> 13;
bool bit12 = ((arm_op & (1 << 12)) >> 12) != 0;
bool bit14 = ((arm_op & (1 << 14)) >> 14) != 0;
uint32 i2 = ~(j2 ^ S) & 1;
uint32 i1 = ~(j1 ^ S) & 1;
bool toARM = bit14 && !bit12;
temp |= (S << 24) | (i1 << 23) | (i2 << 22);
if (temp & 0x01000000) // sign extension
temp |= 0xFE000000;
uint32 prefetch;
if (toARM) {
// Align PC on 4-byte boundary
uint32 align4byte = (rva % 4) ? 2 : 4;
prefetch = align4byte;
} else {
prefetch = 4;
}
temp += prefetch;
(*addr) = temp;
uint32 temp2 = 0x4000;
temp2 |= (arm_op & (1 << 12)) >> 12;
temp2 |= (arm_op & (1 << 14)) >> 13;
temp2 |= (arm_op & (1 << 15)) >> 13;
temp2 |= (arm_op & 0xF8000000) >> 24;
temp2 |= (prefetch & 0x0000000F) << 8;
(*c_op) = temp2;
break;
}
case ARM_OFF21: {
uint32 temp = 0;
temp |= (arm_op & 0x000007FF) << 1; // imm11
temp |= (arm_op & 0x003F0000) >> 4; // imm6
uint32 S = (arm_op & (1 << 26)) >> 26;
uint32 j2 = (arm_op & (1 << 11)) >> 11;
uint32 j1 = (arm_op & (1 << 13)) >> 13;
temp |= (S << 20) | (j1 << 19) | (j2 << 18);
if (temp & 0x00100000) // sign extension
temp |= 0xFFE00000;
temp += 4;
(*addr) = temp;
uint32 temp2 = 0x5000;
temp2 |= (arm_op & 0x03C00000) >> 22; // just save the cond
(*c_op) = temp2;
break;
}
default:
return false;
}
return true;
}
CheckBool DisassemblerElf32ARM::Decompress(ARM_RVA type, uint16 c_op,
uint32 addr, uint32* arm_op) {
// Reverses the process in the compress() method. Takes the
// Courgette op and relative address and reconstructs the original
// ARM or thumb op.
switch (type) {
case ARM_OFF8:
(*arm_op) = ((c_op & 0x0FFF) << 8) | (((addr - 4) >> 1) & 0x000000FF);
break;
case ARM_OFF11:
(*arm_op) = ((c_op & 0x0FFF) << 11) | (((addr - 4) >> 1) & 0x000007FF);
break;
case ARM_OFF24:
(*arm_op) = ((c_op & 0x0FFF) << 24) | (((addr - 8) >> 2) & 0x00FFFFFF);
break;
case ARM_OFF25: {
uint32 temp = 0;
temp |= (c_op & (1 << 0)) << 12;
temp |= (c_op & (1 << 1)) << 13;
temp |= (c_op & (1 << 2)) << 13;
temp |= (c_op & (0xF8000000 >> 24)) << 24;
uint32 prefetch = (c_op & 0x0F00) >> 8;
addr -= prefetch;
addr &= 0x01FFFFFF;
uint32 S = (addr & (1 << 24)) >> 24;
uint32 i1 = (addr & (1 << 23)) >> 23;
uint32 i2 = (addr & (1 << 22)) >> 22;
uint32 j1 = ((~i1) ^ S) & 1;
uint32 j2 = ((~i2) ^ S) & 1;
temp |= S << 26;
temp |= j2 << 11;
temp |= j1 << 13;
temp |= (addr & (0x000007FF << 1)) >> 1;
temp |= (addr & (0x03FF0000 >> 4)) << 4;
(*arm_op) = temp;
break;
}
case ARM_OFF21: {
uint32 temp = 0xF0008000;
temp |= (c_op & (0x03C00000 >> 22)) << 22;
addr -= 4;
addr &= 0x001FFFFF;
uint32 S = (addr & (1 << 20)) >> 20;
uint32 j1 = (addr & (1 << 19)) >> 19;
uint32 j2 = (addr & (1 << 18)) >> 18;
temp |= S << 26;
temp |= j2 << 11;
temp |= j1 << 13;
temp |= (addr & (0x000007FF << 1)) >> 1;
temp |= (addr & (0x003F0000 >> 4)) << 4;
(*arm_op) = temp;
break;
}
default:
return false;
}
return true;
}
uint16 DisassemblerElf32ARM::TypedRVAARM::op_size() const {
switch (type_) {
case ARM_OFF8:
return 2;
case ARM_OFF11:
return 2;
case ARM_OFF24:
return 4;
case ARM_OFF25:
return 4;
case ARM_OFF21:
return 4;
default:
return 0xFFFF;
}
}
CheckBool DisassemblerElf32ARM::TypedRVAARM::ComputeRelativeTarget(
const uint8* op_pointer) {
arm_op_ = op_pointer;
switch (type_) {
case ARM_OFF8:
// Fall through
case ARM_OFF11: {
RVA relative_target;
CheckBool ret = Compress(type_, Read16LittleEndian(op_pointer), rva(),
&c_op_, &relative_target);
set_relative_target(relative_target);
return ret;
}
case ARM_OFF24: {
RVA relative_target;
CheckBool ret = Compress(type_, Read32LittleEndian(op_pointer), rva(),
&c_op_, &relative_target);
set_relative_target(relative_target);
return ret;
}
case ARM_OFF25:
// Fall through
case ARM_OFF21: {
// A thumb-2 op is 32 bits stored as two 16-bit words
uint32 pval = (Read16LittleEndian(op_pointer) << 16)
| Read16LittleEndian(op_pointer + 2);
RVA relative_target;
CheckBool ret = Compress(type_, pval, rva(), &c_op_, &relative_target);
set_relative_target(relative_target);
return ret;
}
default:
return false;
}
}
CheckBool DisassemblerElf32ARM::TypedRVAARM::EmitInstruction(
AssemblyProgram* program,
RVA target_rva) {
return program->EmitRel32ARM(c_op(),
program->FindOrMakeRel32Label(target_rva),
arm_op_,
op_size());
}
DisassemblerElf32ARM::DisassemblerElf32ARM(const void* start, size_t length)
: DisassemblerElf32(start, length) {
}
// Convert an ELF relocation struction into an RVA
CheckBool DisassemblerElf32ARM::RelToRVA(Elf32_Rel rel, RVA* result) const {
// The rightmost byte of r_info is the type...
elf32_rel_arm_type_values type =
(elf32_rel_arm_type_values)(unsigned char)rel.r_info;
// The other 3 bytes of r_info are the symbol
uint32 symbol = rel.r_info >> 8;
switch(type)
{
case R_ARM_RELATIVE:
if (symbol != 0)
return false;
// This is a basic ABS32 relocation address
*result = rel.r_offset;
return true;
default:
return false;
}
}
CheckBool DisassemblerElf32ARM::ParseRelocationSection(
const Elf32_Shdr *section_header,
AssemblyProgram* program) {
// This method compresses a contiguous stretch of R_ARM_RELATIVE
// entries in the relocation table with a Courgette relocation table
// instruction. It skips any entries at the beginning that appear
// in a section that Courgette doesn't support, e.g. INIT.
// Specifically, the entries should be
// (1) In the same relocation table
// (2) Are consecutive
// (3) Are sorted in memory address order
//
// Happily, this is normally the case, but it's not required by spec
// so we check, and just don't do it if we don't match up.
//
// The expectation is that one relocation section will contain
// all of our R_ARM_RELATIVE entries in the expected order followed
// by assorted other entries we can't use special handling for.
bool match = true;
// Walk all the bytes in the section, matching relocation table or not
size_t file_offset = section_header->sh_offset;
size_t section_end = section_header->sh_offset + section_header->sh_size;
Elf32_Rel *section_relocs_iter =
(Elf32_Rel *)OffsetToPointer(section_header->sh_offset);
uint32 section_relocs_count = section_header->sh_size /
section_header->sh_entsize;
if (abs32_locations_.size() > section_relocs_count)
match = false;
if (!abs32_locations_.empty()) {
std::vector<RVA>::iterator reloc_iter = abs32_locations_.begin();
for (uint32 i = 0; i < section_relocs_count; i++) {
if (section_relocs_iter->r_offset == *reloc_iter)
break;
if (!ParseSimpleRegion(file_offset, file_offset + sizeof(Elf32_Rel),
program))
return false;
file_offset += sizeof(Elf32_Rel);
++section_relocs_iter;
}
while (match && (reloc_iter != abs32_locations_.end())) {
if (section_relocs_iter->r_info != R_ARM_RELATIVE ||
section_relocs_iter->r_offset != *reloc_iter)
match = false;
section_relocs_iter++;
reloc_iter++;
file_offset += sizeof(Elf32_Rel);
}
if (match) {
// Skip over relocation tables
if (!program->EmitElfARMRelocationInstruction())
return false;
}
}
return ParseSimpleRegion(file_offset, section_end, program);
}
CheckBool DisassemblerElf32ARM::ParseRel32RelocsFromSection(
const Elf32_Shdr* section_header) {
uint32 start_file_offset = section_header->sh_offset;
uint32 end_file_offset = start_file_offset + section_header->sh_size;
const uint8* start_pointer = OffsetToPointer(start_file_offset);
const uint8* end_pointer = OffsetToPointer(end_file_offset);
// Quick way to convert from Pointer to RVA within a single Section is to
// subtract 'pointer_to_rva'.
const uint8* const adjust_pointer_to_rva = start_pointer -
section_header->sh_addr;
// Find the rel32 relocations.
const uint8* p = start_pointer;
bool on_32bit = 1; // 32-bit ARM ops appear on 32-bit boundaries, so track it
while (p < end_pointer) {
// Heuristic discovery of rel32 locations in instruction stream: are the
// next few bytes the start of an instruction containing a rel32
// addressing mode?
TypedRVAARM* rel32_rva = NULL;
RVA target_rva = 0;
bool found = false;
// 16-bit thumb ops
if (!found && (p + 3) <= end_pointer) {
uint16 pval = Read16LittleEndian(p);
if ((pval & 0xF000) == 0xD000) {
RVA rva = static_cast<RVA>(p - adjust_pointer_to_rva);
rel32_rva = new TypedRVAARM(ARM_OFF8, rva);
if (!rel32_rva->ComputeRelativeTarget((uint8*) p)) {
return false;
}
target_rva = rel32_rva->rva() + rel32_rva->relative_target();
found = true;
} else if ((pval & 0xF800) == 0xE000) {
RVA rva = static_cast<RVA>(p - adjust_pointer_to_rva);
rel32_rva = new TypedRVAARM(ARM_OFF11, rva);
if (!rel32_rva->ComputeRelativeTarget((uint8*) p)) {
return false;
}
target_rva = rel32_rva->rva() + rel32_rva->relative_target();
found = true;
}
}
// thumb-2 ops comprised of two 16-bit words
if (!found && (p + 5) <= end_pointer) {
// This is really two 16-bit words, not one 32-bit word.
uint32 pval = (Read16LittleEndian(p) << 16) | Read16LittleEndian(p + 2);
if ((pval & 0xF8008000) == 0xF0008000) {
// Covers thumb-2's 32-bit conditional/unconditional branches
if ( (pval & (1 << 14)) || (pval & (1 << 12)) ) {
// A branch, with link, or with link and exchange.
RVA rva = static_cast<RVA>(p - adjust_pointer_to_rva);
rel32_rva = new TypedRVAARM(ARM_OFF25, rva);
if (!rel32_rva->ComputeRelativeTarget((uint8*) p)) {
return false;
}
target_rva = rel32_rva->rva() + rel32_rva->relative_target();
found = true;
} else {
// TODO(paulgazz) make sure cond is not 111
// A conditional branch instruction
RVA rva = static_cast<RVA>(p - adjust_pointer_to_rva);
rel32_rva = new TypedRVAARM(ARM_OFF21, rva);
if (!rel32_rva->ComputeRelativeTarget((uint8*) p)) {
return false;
}
target_rva = rel32_rva->rva() + rel32_rva->relative_target();
found = true;
}
}
}
// 32-bit ARM ops
if (!found && on_32bit && (p + 5) <= end_pointer) {
uint32 pval = Read32LittleEndian(p);
if ((pval & 0x0E000000) == 0x0A000000) {
// Covers both 0x0A 0x0B ARM relative branches
RVA rva = static_cast<RVA>(p - adjust_pointer_to_rva);
rel32_rva = new TypedRVAARM(ARM_OFF24, rva);
if (!rel32_rva->ComputeRelativeTarget((uint8*) p)) {
return false;
}
target_rva = rel32_rva->rva() + rel32_rva->relative_target();
found = true;
}
}
if (found && IsValidRVA(target_rva)) {
rel32_locations_.push_back(rel32_rva);
#if COURGETTE_HISTOGRAM_TARGETS
++rel32_target_rvas_[target_rva];
#endif
p += rel32_rva->op_size();
// A tricky way to update the on_32bit flag. Here is the truth table:
// on_32bit | on_32bit size is 4
// ---------+---------------------
// 1 | 0 0
// 0 | 0 1
// 0 | 1 0
// 1 | 1 1
on_32bit = (~(on_32bit ^ (rel32_rva->op_size() == 4))) != 0;
} else {
// Move 2 bytes at a time, but track 32-bit boundaries
p += 2;
on_32bit = ((on_32bit + 1) % 2) != 0;
}
}
return true;
}
} // namespace courgette