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Handle branch fallthrough

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This commit is contained in:
Sajid
2024-09-09 22:52:34 +06:00
parent 60edcad576
commit 267e19b854
5 changed files with 71 additions and 27 deletions
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62
PowerAnalyse/function.cpp
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@@ -3,7 +3,7 @@
#include <vector>
#include <bit>
size_t function::SearchBlock(size_t address) const
size_t Function::SearchBlock(size_t address) const
{
if (address < base)
{
@@ -25,18 +25,22 @@ size_t function::SearchBlock(size_t address) const
return -1;
}
function function::Analyze(const void* code, size_t size, size_t base)
Function Function::Analyze(const void* code, size_t size, size_t base)
{
function fn{ base, 0 };
Function fn{ base, 0 };
auto& blocks = fn.blocks;
blocks.reserve(8);
blocks.emplace_back();
const auto* data = (uint32_t*)code;
const auto* dataStart = data;
const auto* dataEnd = (uint32_t*)((uint8_t*)code + size);
std::vector<size_t> blockStack{};
blockStack.reserve(32);
blockStack.emplace_back();
#define RESTORE_DATA() if (!blockStack.empty()) data = (dataStart + (blocks[blockStack.back()].base / sizeof(*data))) - 1; // continue adds one
// TODO: Branch fallthrough
for (; data <= dataEnd ; ++data)
{
@@ -46,6 +50,7 @@ function function::Analyze(const void* code, size_t size, size_t base)
break; // it's hideover
}
auto& curBlock = blocks[blockStack.back()];
const auto instruction = std::byteswap(*data);
const auto op = PPC_OP(instruction);
@@ -55,12 +60,28 @@ function function::Analyze(const void* code, size_t size, size_t base)
ppc_insn insn;
ppc::Disassemble(data, addr, insn);
blocks[blockStack.back()].size += 4;
if (curBlock.base == 0x28)
{
printf("");
}
if (curBlock.projectedSize != -1 && curBlock.size >= curBlock.projectedSize) // fallthrough
{
blockStack.pop_back();
RESTORE_DATA();
continue;
}
curBlock.size += 4;
if (op == PPC_OP_BC) // conditional branches all originate from one opcode, thanks RISC
{
// this one ends here
blockStack.pop_back();
if (isLink) // just a conditional call, nothing to see here
{
continue;
}
curBlock.projectedSize = -1;
blockStack.pop_back();
// true/false paths
// left block: false case
// right block: true case
@@ -73,7 +94,7 @@ function function::Analyze(const void* code, size_t size, size_t base)
if (lBlock == -1)
{
blocks.emplace_back(lBase, 0);
blocks.emplace_back(lBase, 0).projectedSize = rBase - lBase;
lBlock = blocks.size() - 1;
}
@@ -83,21 +104,18 @@ function function::Analyze(const void* code, size_t size, size_t base)
blockStack.emplace_back(lBlock);
}
if (!isLink) // not a call, scan this too
auto rBlock = fn.SearchBlock(base + rBase);
if (rBlock == -1)
{
auto rBlock = fn.SearchBlock(base + rBase);
if (rBlock == -1)
{
blocks.emplace_back(insn.operands[1] - base, 0);
rBlock = blocks.size() - 1;
blocks.emplace_back(insn.operands[1] - base, 0);
rBlock = blocks.size() - 1;
blockStack.emplace_back(rBlock);
}
blockStack.emplace_back(rBlock);
}
if (!blockStack.empty())
{
data = (dataStart + (blocks[blockStack.back()].base / sizeof(*data))) - 1; // loop will add one
RESTORE_DATA();
}
}
else if (op == PPC_OP_B || (op == PPC_OP_CTR && xop == 16) || instruction == 0) // b, blr, end padding
@@ -113,16 +131,24 @@ function function::Analyze(const void* code, size_t size, size_t base)
const auto branchBase = insn.operands[0] - base;
const auto branchBlock = fn.SearchBlock(insn.operands[0]);
const auto isContinious = branchBase == curBlock.base + curBlock.size;
auto sizeProjection = (size_t)-1;
if (isContinious && curBlock.projectedSize != -1)
{
sizeProjection = curBlock.projectedSize - curBlock.size;
}
if (branchBlock == -1)
{
blocks.emplace_back(branchBase, 0);
blocks.emplace_back(branchBase, 0, sizeProjection);
blockStack.emplace_back(blocks.size() - 1);
}
}
if (!blockStack.empty())
{
data = (dataStart + (blocks[blockStack.back()].base / sizeof(*data))) - 1;
RESTORE_DATA();
}
}
}

15
PowerAnalyse/function.h
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@@ -1,18 +1,21 @@
#pragma once
#include <vector>
struct function
struct Function
{
struct block
struct Block
{
size_t base;
size_t size;
size_t base{};
size_t size{};
// scratch
size_t projectedSize{ static_cast<size_t>(-1) };
};
size_t base{};
size_t size{};
std::vector<block> blocks{};
std::vector<Block> blocks{};
size_t SearchBlock(size_t address) const;
static function Analyze(const void* code, size_t size, size_t base);
static Function Analyze(const void* code, size_t size, size_t base);
};

6
PowerAnalyse/main.cpp
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@@ -7,7 +7,7 @@
int main()
{
const auto file = LoadFile("cond.elf");
const auto file = LoadFile("cond-fall.elf");
auto image = Image::ParseImage(file.data(), file.size()).value();
for (const auto& section : image.sections)
@@ -20,7 +20,7 @@ int main()
//ppc::Disassemble(c, 0x831D6C64, insn);
//std::println("{:20}{}", insn.opcode->name, insn.op_str);
std::vector<function> functions;
std::vector<Function> functions;
for (const auto& section : image.sections)
{
if (!(section.flags & SectionFlags_Code))
@@ -40,7 +40,7 @@ int main()
continue;
}
const auto& fn = functions.emplace_back(function::Analyze(data, dataEnd - data, base));
const auto& fn = functions.emplace_back(Function::Analyze(data, dataEnd - data, base));
data += fn.size;
base += fn.size;

15
tests/PowerAnalyse/cond-fall.cpp Normal file
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@@ -0,0 +1,15 @@
int cond(int a)
{
int v = 2;
if (a == 1)
{
v += 5;
}
return v;
}
extern "C" int _start()
{
return cond(0);
}

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tests/PowerAnalyse/cond-fall.elf Normal file
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