Retro68/Elf2Mac/Section.cc

/*
	 Copyright 2017 Wolfgang Thaller.

	 This file is part of Retro68.

	 Retro68 is free software: you can redistribute it and/or modify
	 it under the terms of the GNU General Public License as published by
	 the Free Software Foundation, either version 3 of the License, or
	 (at your option) any later version.

	 Retro68 is distributed in the hope that it will be useful,
	 but WITHOUT ANY WARRANTY; without even the implied warranty of
	 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	 GNU General Public License for more details.

	 You should have received a copy of the GNU General Public License
	 along with Retro68.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "Section.h"

#include "Symbol.h"
#include "Reloc.h"
#include "Object.h"
#include "Symtab.h"

#include <algorithm>
#include <sstream>
#include <assert.h>
#include <iostream>

#include "BinaryIO.h"

using std::string;

Section::~Section()
{
}

Section::Section(Object& theObject, string name, int idx, SectionKind kind, Elf_Scn *elfsec)
    : theObject(theObject),
      name(name), idx(idx), kind(kind), elfsec(elfsec), relasec(NULL),
      exceptionInfoStart(0),
      codeID(-1), firstJTEntryIndex(0)
{
	data = elf_getdata(elfsec, NULL);
	gelf_getshdr(elfsec, &shdr);
	outputBase = shdr.sh_addr;
}


void Section::SetRela(Elf_Scn *scn)
{
	relasec = scn;
	GElf_Shdr rshdr;
	gelf_getshdr(relasec, &rshdr);

	int nRela = rshdr.sh_size / rshdr.sh_entsize;
	Elf_Data *data = elf_getdata(relasec, NULL);
	for(int i = 0; i < nRela; i++)
	{
		GElf_Rela rela;
		gelf_getrela(data, i, &rela);

		if(rela.r_offset < shdr.sh_addr || rela.r_offset >= shdr.sh_addr + shdr.sh_size)
		{
			// For some reason, there sometimes are relocations beyond the end of the sections
			// in LD output. That's bad. Let's ignore it.
			continue;
		}
		relocs.push_back(rela);
	}

	std::sort(relocs.begin(), relocs.end(),
	          [](GElf_Rela& a, GElf_Rela& b) { return a.r_offset < b.r_offset; });
}

uint32_t Section::GetSize()
{
	return data->d_size;
}

string Section::GetData()
{
	return string((char*)data->d_buf, (char*)data->d_buf + data->d_size);
}

std::vector<RuntimeReloc> Section::GetRelocations(bool useOffsets)
{
	std::vector<RuntimeReloc> outRelocs;

	for(auto& rela : relocs)
	{
		//printf("rel: %d %d %x %x\n", (int)GELF_R_TYPE(rela.r_info), (int)GELF_R_SYM(rela.r_info), (unsigned)rela.r_addend, (unsigned)rela.r_offset);

		int symidx = GELF_R_SYM(rela.r_info);
		if(symidx == 0)
			continue;

		Symbol& sym = theObject.symtab->GetSym(symidx);

		if(sym.st_shndx == SHN_UNDEF || sym.st_shndx >= SHN_LORESERVE)
			continue;
		if(sym.sectionKind == SectionKind::undefined)
			continue;

		if(GELF_R_TYPE(rela.r_info) == R_68K_32)
		{
			assert(sym.sectionKind != SectionKind::undefined);

			uint32_t offset = rela.r_offset;
			if(useOffsets)
				offset -= shdr.sh_addr;

			//longword(out, offset | ((int)rela.relocBase << 24));
			outRelocs.emplace_back(rela.relocBase, offset);
		}
	}

	return outRelocs;
}

void Section::ScanRelocs()
{
	for(Reloc& rela : relocs)
	{
		int symidx = GELF_R_SYM(rela.r_info);
		if(symidx == 0)
			continue;

		Symbol *sym = &theObject.symtab->GetSym(symidx);

		if(sym->st_shndx == SHN_UNDEF)
			continue;

		if(rela.r_addend != 0)
		{
			int symidx2 = theObject.symtab->FindSym(sym->st_shndx, sym->st_value + rela.r_addend);
			if(symidx2 != -1)
			{
				sym = &theObject.symtab->GetSym(symidx2);
				rela.r_addend = 0;
				rela.r_info = GELF_R_INFO(symidx2, GELF_R_TYPE(rela.r_info));

			}
		}

		if(sym->st_shndx != idx)
			sym->referencedExternally = true;
	}
}

void Section::FixRelocs(bool allowDirectCodeRefs)
{
	for(Reloc& rela : relocs)
	{
		if(GELF_R_TYPE(rela.r_info) != R_68K_32)
			continue;

		int symidx = GELF_R_SYM(rela.r_info);
		if(symidx == 0)
			continue;
		Symbol& sym = theObject.symtab->GetSym(symidx);

		if(sym.sectionKind == SectionKind::undefined)
			continue;

		RelocBase relocBase;
		switch(sym.sectionKind)
		{
			case SectionKind::code:
				relocBase = RelocBase::code;
				if(sym.needsJT && (exceptionInfoStart == 0 || rela.r_offset < exceptionInfoStart || sym.name == "__gxx_personality_v0"))
				{
					if(rela.r_addend == 0)
					{
						relocBase = RelocBase::jumptable;
					}
					else
					{
						if(sym.section.get() != this)
						{
							std::cerr << "Invalid ref from "
							          << name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec
							          << " to " << sym.section->name
							          << "(" << sym.name << ")"
							          << "+" << rela.r_offset << std::endl;
						}
						assert(sym.section.get() == this);
					}
				}
				else if(!allowDirectCodeRefs)
				{
					if(sym.section.get() != this)
					{
						std::cerr << "Invalid ref from "
						          << name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec
						          << " to " << sym.section->name
						          << "(" << sym.name << ")"
						          << "+" << rela.r_offset << std::endl;
						std::cerr << "needsJT: " << (sym.needsJT ? "true" : "false") << std::endl;
						std::cerr << "from addr: " << rela.r_offset << ", exceptionInfoStart: " << exceptionInfoStart << std::endl;

					}
					assert(sym.section.get() == this);
				}
				break;
			case SectionKind::data:
				relocBase = RelocBase::data;
				break;
			case SectionKind::bss:
				relocBase = RelocBase::bss;
				break;
			case SectionKind::undefined:
				assert(false);
				break;
		}
		rela.relocBase = relocBase;

		uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr);

		if(relocBase == RelocBase::jumptable)
		{
			uint32_t dst = 0x20 + sym.jtIndex * 8 + 2;
			relocand[0] = dst >> 24;
			relocand[1] = dst >> 16;
			relocand[2] = dst >> 8;
			relocand[3] = dst;
		}
		else
		{
			uint32_t orig = (relocand[0] << 24) | (relocand[1] << 16) | (relocand[2] << 8) | relocand[3];
			uint32_t dst = orig + sym.section->outputBase - sym.section->shdr.sh_addr;
			relocand[0] = dst >> 24;
			relocand[1] = dst >> 16;
			relocand[2] = dst >> 8;
			relocand[3] = dst;
		}
	}
}