UnrealEngineUWP/Engine/Source/Programs/UnrealBuildAccelerator/Common/Private/UbaObjectFileElf.cpp

// Copyright Epic Games, Inc. All Rights Reserved.

#include "UbaObjectFileElf.h"
#include "UbaFileAccessor.h"

namespace uba
{
	struct Elf64Header
	{
	  unsigned char	e_ident[16];	/* Magic number and other info */
	  u16	e_type;			/* Object file type */
	  u16	e_machine;		/* Architecture */
	  u32	e_version;		/* Object file version */
	  u64	e_entry;		/* Entry point virtual address */
	  u64	e_phoff;		/* Program header table file offset */
	  u64	e_shoff;		/* Section header table file offset */
	  u32	e_flags;		/* Processor-specific flags */
	  u16	e_ehsize;		/* ELF header size in bytes */
	  u16	e_phentsize;	/* Program header table entry size */
	  u16	e_phnum;		/* Program header table entry count */
	  u16	e_shentsize;	/* Section header table entry size */
	  u16	e_shnum;		/* Section header table entry count */
	  u16	e_shstrndx;		/* Section header string table index */
	};

	struct Elf64SectionHeader
	{
	  u32	sh_name;		/* Section name (string tbl index) */
	  u32	sh_type;		/* Section type */
	  u64	sh_flags;		/* Section flags */
	  u64	sh_addr;		/* Section virtual addr at execution */
	  u64	sh_offset;		/* Section file offset */
	  u64	sh_size;		/* Section size in bytes */
	  u32	sh_link;		/* Link to another section */
	  u32	sh_info;		/* Additional section information */
	  u64	sh_addralign;	/* Section alignment */
	  u64	sh_entsize;		/* Entry size if section holds table */
	};

	struct Elf64Sym
	{
	  u32	st_name;		/* Symbol name (string tbl index) */
	  u8	st_info;		/* Symbol type and binding */
	  u8	st_other;		/* Symbol visibility */
	  u16	st_shndx;		/* Section index */
	  u64	st_value;		/* Symbol value */
	  u64	st_size;		/* Symbol size */
	};

	#define EM_X86_64	62	/* AMD x86-64 architecture */

	#define SHT_SYMTAB	  2		/* Symbol table */
	#define SHT_DYNSYM	  11		/* Dynamic linker symbol table */

	#define STT_OBJECT	1		/* Symbol is a data object */
	#define STT_FUNC	2		/* Symbol is a code object */
	
	#define STB_WEAK	2		/* Weak symbol */


	#define ELF32_ST_BIND(val)		(((unsigned char) (val)) >> 4)
	#define ELF32_ST_TYPE(val)		((val) & 0xf)
	#define ELF32_ST_INFO(bind, type)	(((bind) << 4) + ((type) & 0xf))

	/* Both Elf32_Sym and Elf64_Sym use the same one-byte st_info field.  */
	#define ELF64_ST_BIND(val)		ELF32_ST_BIND (val)
	#define ELF64_ST_TYPE(val)		ELF32_ST_TYPE (val)
	#define ELF64_ST_INFO(bind, type)	ELF32_ST_INFO ((bind), (type))

	// These are symbols that are added to all dlls through some macros.
	// When merging dlls we need to remove duplicates of these
	UnorderedSymbols ObjectFileElf::PotentiallyDuplicatedSymbols = 
	{
#if 0 // This is not needed anymore
		// REPLACEMENT_OPERATOR_NEW_AND_DELETE
		"_Znwm",
		"_Znam",
		"_ZnwmRKSt9nothrow_t",
		"_ZnamRKSt9nothrow_t",
		"_ZnwmSt11align_val_t",
		"_ZnamSt11align_val_t",
		"_ZnwmSt11align_val_tRKSt9nothrow_t",
		"_ZnamSt11align_val_tRKSt9nothrow_t",
		"_ZdlPv",
		"_ZdaPv",
		"_ZdlPvRKSt9nothrow_t",
		"_ZdaPvRKSt9nothrow_t",
		"_ZdlPvm",
		"_ZdaPvm",
		"_ZdlPvmRKSt9nothrow_t",
		"_ZdaPvmRKSt9nothrow_t",
		"_ZdlPvSt11align_val_t",
		"_ZdaPvSt11align_val_t",
		"_ZdlPvSt11align_val_tRKSt9nothrow_t",
		"_ZdaPvSt11align_val_tRKSt9nothrow_t",
		"_ZdlPvmSt11align_val_t",
		"_ZdaPvmSt11align_val_t",
		"_ZdlPvmSt11align_val_tRKSt9nothrow_t",
		"_ZdaPvmSt11align_val_tRKSt9nothrow_t",

		// UE_DEFINE_FMEMORY_WRAPPERS
		"_Z14FMemory_Mallocmm",
		"_Z15FMemory_ReallocPvmm",
		"_Z12FMemory_FreePv",

		// UE4_VISUALIZERS_HELPERS
		"GNameBlocksDebug",
		"GObjectIndexToPackedObjectRefDebug",
		"GObjectArrayForDebugVisualizers",
		"GComplexObjectPathDebug",
		"GObjectHandlePackageDebug",
#endif
	};

	ObjectFileElf::ObjectFileElf()
	{
		m_type = ObjectFileType_Elf;
	}


	bool ObjectFileElf::Parse(Logger& logger, const tchar* filename)
	{
		auto& header = *(Elf64Header*)m_data;
		if (header.e_ident[4] != 2) // 64-bit
			return false;
		if (header.e_ident[5] != 1) // Little endian
			return false;
		if (header.e_ident[6] != 1) // Version
			return false;
		if (header.e_type != 1) // Relocatable file
			return false;

		UBA_ASSERT(sizeof(Elf64SectionHeader) == header.e_shentsize);

		auto sections = (Elf64SectionHeader*)(m_data + header.e_shoff);

		auto& namesSection = sections[header.e_shstrndx];
		u8* stringTableData = m_data + namesSection.sh_offset;

		#if 0
		u64 stringTableSize = namesSection.sh_size;
		u32 counter = 0;
		char* it = (char*)stringTableData;
		char* end = it + stringTableSize;
		while (it != end)
		{
			printf("%s\n", it);
			u64 len = strlen(it);
			it += len + 1;
			counter++;
		}
		#endif

		for (u16 i=0; i!=header.e_shnum; ++i)
		{
			auto& section = sections[i];
			//auto sectionName = (char*)stringTableData + section.sh_name;

			if (section.sh_type == SHT_SYMTAB || section.sh_type == SHT_DYNSYM)
			{
				UBA_ASSERT(section.sh_link == header.e_shstrndx);
				UBA_ASSERT(section.sh_entsize == sizeof(Elf64Sym));
				auto symbols = (Elf64Sym*)(m_data + section.sh_offset);
				u64 symbolCount = section.sh_size / sizeof(Elf64Sym);
				for (u64 j=0; j!=symbolCount; ++j)
				{
					auto& symbol = symbols[j];
					u8 symbolType = ELF64_ST_TYPE(symbol.st_info);
					if (symbolType != STT_FUNC && symbolType != STT_OBJECT)
						continue;

					auto name = (char*)stringTableData + symbol.st_name;
					if (PotentiallyDuplicatedSymbols.find(name) == PotentiallyDuplicatedSymbols.end())
						continue;

					m_potentialDuplicates.emplace(name);
				}
			}
		}
		return true;
	}
	/*
	bool ObjectFileElf::CreateStripped(Logger& logger, const tchar* newFilename, const UnorderedSymbols& allNeededImports, u32& outKeptExportCount)
	{
		FileAccessor newFile(logger, newFilename);
		if (!newFile.CreateMemoryWrite(false, DefaultAttributes(), m_dataSize))
			return false;

		u8* newData = newFile.GetData();
		memcpy(newData, m_data, m_dataSize);

		auto& header = *(Elf64Header*)newData;
		auto sections = (Elf64SectionHeader*)(newData + header.e_shoff);

		auto& namesSection = sections[header.e_shstrndx];
		u8* stringTableData = newData + namesSection.sh_offset;

		for (u16 i=0; i!=header.e_shnum; ++i)
		{
			auto& section = sections[i];

			if (section.sh_type == SHT_SYMTAB || section.sh_type == SHT_DYNSYM)
			{
				UBA_ASSERT(section.sh_link == header.e_shstrndx);
				UBA_ASSERT(section.sh_entsize == sizeof(Elf64Sym));
				auto symbols = (Elf64Sym*)(newData + section.sh_offset);
				u64 symbolCount = section.sh_size / sizeof(Elf64Sym);
				for (u64 j=0; j!=symbolCount; ++j)
				{
					auto& symbol = symbols[j];
					u8 symbolType = ELF64_ST_TYPE(symbol.st_info);
					if (symbolType != STT_FUNC && symbolType != STT_OBJECT)
						continue;
					auto name = (char*)stringTableData + symbol.st_name;

					if (m_toRemove.find(name) == m_toRemove.end())
						continue;
					symbol.st_info = ELF64_ST_INFO(STB_WEAK, symbolType);
				}
			}
		}

		return newFile.Close();
	}
	*/
	bool ObjectFileElf::StripExports(Logger& logger, u8* newData, const UnorderedSymbols& allNeededImports, u32& outKeptExportCount)
	{
		return true;
	}

	bool ObjectFileElf::CreateExtraFile(Logger& logger, MemoryBlock& memoryBlock, const UnorderedSymbols& allNeededImports, const UnorderedSymbols& allSharedImports, const UnorderedExports& allSharedExports, bool includeExportsInFile)
	{
		auto& header = *(Elf64Header*)memoryBlock.Allocate(sizeof(Elf64Header), 1, TC(""));

		header.e_ident[0] = 0x7f;
		header.e_ident[1] = 'E';
		header.e_ident[2] = 'L';
		header.e_ident[3] = 'F';
		header.e_ident[4] = 2;
		header.e_ident[5] = 1;
		header.e_ident[6] = 1;
		header.e_type = 1;
		header.e_machine = EM_X86_64;
		header.e_ehsize = sizeof(Elf64Header);
		return true;
	}
}