// -----------------------------------------------------------------------------

 // - IDA Pro Script -

 // Name: gcc_fpic.idc

 // By: Damaged Soul

 // Desc: Add references for strings, variables, and other data that seem mangled

 //       due to GCC's -fPIC option and the .got section of an x86 ELF binary.

 // 

 // Version History

 // 1.0 [2007-11-22]

 //     - Initial Version

 // 1.1 [2008-05-02]

 //     - Now works with GCC 4.x compiled binaries

 // 1.2 [2008-11-06]

 //     - Now works with GCC 4.3 compiled binaries

 //     - Fixed: Redefining alignment blocks as data caused IDA to pop up

 //       an annoying warning

 // -----------------------------------------------------------------------------

 #include <idc.idc>

 #define REG_NONE 0

 #define REG_EAX 1

 #define REG_EBX 2

 #define REG_ECX 3

 #define REG_EDX 4

 #define OP_ADD 1

 #define OP_SUB 2

 #define OPFORMAT_STRING 1

 #define OPFORMAT_DEREF  2

 #define OPFORMAT_NORMAL 3

 static main()

 {

 	auto filetype, compiler, demang, strPrefix;

 	auto seg, codeStart, codeEnd, roStart, roEnd, gotStart, gotEnd, opformat;

 	auto addr, funcend, whichop, reg, tempstr;

 	auto operand1, operand2, opval, opstr, dataAddr, flags, count;

 	SetStatus(IDA_STATUS_WORK);

 	Message("Starting scan for -fPIC code...\n");

 	/* Check file type and compiler */

 	filetype = GetShortPrm(INF_FILETYPE);

 	if (filetype != FT_ELF)

 	{

 		Message("Scan aborted. Input file must be using ELF binary format!\n");

 		SetStatus(IDA_STATUS_READY);

 		return;

 	}

 	compiler = GetCharPrm(INF_COMPILER);

 	if (compiler != COMP_GNU)

 	{

 		Message("Scan aborted. Input file must have been compiled with GNU GCC/G++!\n");

 		SetStatus(IDA_STATUS_READY);

 		return;

 	}

 	/* 

 	 * If the GCC v3.x names option is not set, then set it first.

 	 *

 	 * :TODO: Need to change this if GCC 2.95 support is to be added.

 	 */

 	demang = GetCharPrm(INF_DEMNAMES);

 	if ((demang & DEMNAM_GCC3) == 0)

 	{

 		SetCharPrm(INF_DEMNAMES, demang | DEMNAM_GCC3);

 	}

 	/* Get string prefix */

 	strPrefix = GetCharPrm(INF_ASCIIPREF);

 	/* Get address of first section in binary */

 	seg = FirstSeg();

 	/* Iterate through all sections and get address of .text, .rodata, and .got */

 	while (seg != BADADDR)

 	{

 		if (SegName(seg) == ".text")

 		{

 			codeStart = seg;

 			codeEnd = NextSeg(seg);

 			Message("%08.8Xh - %08.8Xh: .text\n", codeStart, codeEnd);

 		}

 		else if (SegName(seg) == ".rodata")

 		{

 			roStart = seg;

 			roEnd = NextSeg(seg);

 			Message("%08.8Xh - %08.8Xh: .rodata\n", roStart, roEnd);

 		}

 		else if (SegName(seg) == "abs")

 		{

 			addr = FindText(seg, SEARCH_DOWN|SEARCH_CASE|SEARCH_NOSHOW, 0, 0, "_GLOBAL_OFFSET_TABLE_");

 			gotStart = Dword(addr);

 			gotEnd = NextSeg(gotStart);

 			Message("%08.8Xh - %08.8Xh: .got\n", gotStart, gotEnd);

 		}

 		seg = NextSeg(seg);

 	}

 	addr = codeStart;

 	funcend = -1;

 	count = 0;

 	/**

 	 * Go through .text section while looking for anything like [e?x+blah] or [e?x-blah].

 	 *

 	 * The eax, ebx, ecx, or edx registers are used for storing the address of the .got

 	 * section with -fPIC code. An offset, either negative or positive is added to e?x.

 	 * This results in the address of a string, variable, or other type of data.

 	 *

 	 * In order to determine which register .got will be stored in, one can look at which

 	 * __i686.get_pc_thunk.? function is called near the beginning of each function. The

 	 * suffix on this function is either ax, bx, cx, or dx and corresponds to eax, ebx, 

 	 * ecx, or edx.

 	 */

 	while (addr <= codeEnd)

 	{		

 		operand1 = GetOpnd(addr, 0);

 		operand2 = GetOpnd(addr, 1);

 		whichop = -1;

 		/* Get function end */

 		if (FindFuncEnd(addr) != funcend)

 		{

 			reg = REG_NONE;

 			funcend = FindFuncEnd(addr);

 		}

 		/* Get current PIC register */

 		reg = GetPICRegister(addr, reg, funcend);

 		if (reg != REG_NONE)

 		{

 			/* Search first operand for substring containing PIC register and either a plus or minus sign */

 			if (strstr(operand1, GetPICSearchString(reg, OP_ADD)) != -1 || strstr(operand1, GetPICSearchString(reg, OP_SUB)) != -1)

 			{

 				whichop = 0;

 			}

 			/* Search second operand for substring containing PIC register and either a plus or minus sign */

 			if (strstr(operand2, GetPICSearchString(reg, OP_ADD)) != -1 || strstr(operand2, GetPICSearchString(reg, OP_SUB)) != -1)

 			{

 				whichop = 1;

 			}

 		}

 		if (whichop != -1)

 		{

 			/* Get .got offset */

 			opval = GetOperandValue(addr, whichop);

 			/* Get address inside .got */

 			dataAddr = gotStart + opval;

 			/* Get name at address if it exists */

 			opstr = Name(dataAddr);

 			/* If name doesn't exist then... */

 			if (opstr == "")

 			{	

 				/* 

 				 * Check address to see if it falls in .rodata section.

 				 * If it does, then try to make it a string which will automatically give it a name.

 				 */

 				if (dataAddr >= roStart && dataAddr <= roEnd && MakeStr(dataAddr, BADADDR))

 				{

 					/* Get automatically created name */

 					opstr = Name(dataAddr);

 					opformat = OPFORMAT_STRING;

 					/*

 					 * Sometimes IDA creates a string successfully but not exactly in the right place.

 					 * Uncertain as to why this is (perhaps an IDA bug?), but usually the string in 

 					 * question is a bunch of garbage.

 					 */

 					if (opstr == "")

 					{

 						/* Create a name based on the address */

 						opstr = form("unk_%X", dataAddr);

 						if (strstr(GetDisasm(dataAddr), "align") != -1)

 						{

 							MakeUnkn(dataAddr, DOUNK_SIMPLE);

 						}

 						MakeNameEx(dataAddr, opstr, SN_NOCHECK|SN_NOLIST|SN_NOWARN);

 						opformat = OPFORMAT_DEREF;

 					}

 				}

 				else

 				{

 					/* 

 					 * If address didn't fall into .rodata and the string creation was unsuccessful,

 					 * then try to read the address at 'addr' and get the name of that.

 					 */

 					opstr = Name(Dword(dataAddr));

 					if (opstr == "")

 					{

 						/* If name doesn't exist for that, then create name based on address */

 						opstr = form("unk_%X", dataAddr);

 						if (strstr(GetDisasm(dataAddr), "align") != -1)

 						{

 							MakeUnkn(dataAddr, DOUNK_SIMPLE);

 						}

 						MakeNameEx(dataAddr, opstr, SN_NOCHECK|SN_NOLIST|SN_NOWARN);

 						opformat = OPFORMAT_DEREF;

 					}

 					else

 					{

 						/* If the name did exist at this point, then use it */

 						opformat = OPFORMAT_NORMAL;

 					}

 				}

 			}

 			else

 			{

 				/* If the name at the original address does exist then ... */

 				flags = GetFlags(dataAddr);

 				/* 

 				 * If this address falls into .rodata section and is considered an existing string

 				 * then the replacement operand needs to shown as a string.

 				 */ 

 				if (dataAddr >= roStart && dataAddr <= roEnd && strPrefix != "" && strstr(opstr, strPrefix) == 0)

 				{

 					opformat = OPFORMAT_STRING;

 				}

 				else

 				{

 					opformat = OPFORMAT_DEREF;

 				}

 			}

 			/*

 			 * Try to demangle the name that was found or created above and print it as sort of

 			 * a status message to show the the script is still doing work as this usually

 			 * can take awhile.

 			 */

 			tempstr = Demangle(opstr, INF_LONG_DN);

 			if (tempstr != "")

 			{

 				Message("%8.8Xh: %s\n", addr, tempstr);

 			}

 			else

 			{

 				Message("%8.8Xh: %s\n", addr, opstr);

 			}

 			/*

 			 * The operand that was found to have the PIC register will now be replaced

 			 * with more descriptive text. The format of this text depends upon the value

 			 * of opformat.

 			 */

 			OpAlt(addr, whichop, DoOperandFormat(opformat, opstr));

 			count++;

 		}

 		addr++;

 	}

 	Message("Scan for PIC code is complete! Found %d data items referenced via PIC register.\n", count);

 	Message("Please re-open the database so that newly found strings will appear in the Strings window\n");

 	SetStatus(IDA_STATUS_READY);

 }

 /*

  * Tries to determine the current PIC register given the current address being processed

  * and the previous PIC register.

  */

 static GetPICRegister(addr, previous, funcend)

 {

 	auto assemblyStr, idx, reg, ab;

 	assemblyStr = GetDisasm(addr);

 	if ((idx = strstr(assemblyStr, "call    __i686_get_pc_thunk_")) != -1)

 	{

 		/* 28 is the length of the above string */ 

 		reg = substr(assemblyStr, idx + 28, 30);

 	}

 	else if (strstr(assemblyStr, "call    $+5") != -1)

 	{

 		assemblyStr = GetDisasm(NextHead(addr, funcend));

 		reg = substr(assemblyStr, 9, 11);

 	}

 	if (reg == "ax")

 	{

 		return REG_EAX;

 	}

 	else if (reg == "bx")

 	{

 		return REG_EBX;

 	}

 	else if (reg == "cx")

 	{

 		return REG_ECX;

 	}

 	else if (reg == "dx")

 	{

 		return REG_EDX;

 	}

 	return previous;

 }

 /*

  * Returns a string that is used as a substring search containing the specified

  * PIC register and operator (+ or -).

  */

 static GetPICSearchString(reg, operator)

 {

 	if (reg == REG_EAX)

 	{

 		if (operator == OP_ADD)

 		{

 			return "[eax+";

 		}

 		else if (operator == OP_SUB)

 		{

 			return "[eax-";

 		}

 	}

 	else if (reg == REG_EBX)

 	{

 		if (operator == OP_ADD)

 		{

 			return "[ebx+";

 		}

 		else if (operator == OP_SUB)

 		{

 			return "[ebx-";

 		}

 	}

 	else if (reg == REG_ECX)

 	{

 		if (operator == OP_ADD)

 		{

 			return "[ecx+";

 		}

 		else if (operator == OP_SUB)

 		{

 			return "[ecx-";

 		}

 	}

 	else if (reg == REG_EDX)

 	{

 		if (operator == OP_ADD)

 		{

 			return "[edx+";

 		}

 		else if (operator == OP_SUB)

 		{

 			return "[edx-";

 		}

 	}

 }

 /*

  * Returns a formatted string depending upon the value of the format param.

  * This will be the replacement for the operand containing the PIC register.

  *

  * OPFORMAT_STRING: The referenced data address is a string in the .rodata section.

  * OPFORMAT_DEREF:  The referenced data address has a name. The PIC register operand is

  *                  deferenced so the dereference brackets are shown in the returned string.

  * OPFORMAT_NORMAL: The referenced data address does not have a name. But upon reading

  *                  the address at the referenced data address, it is discovered that that

  *                  address does have a name. There are no dereference brackets because the

  *                  referenced data address had to be read in order to discover a name.

  */

 static DoOperandFormat(format, str)

 {

 	if (format == OPFORMAT_STRING)

 	{

 		return form("offset %s", str);

 	}

 	else if (format == OPFORMAT_DEREF)

 	{

 		return form("[ds:%s]", str);

 	}

 	else if (format == OPFORMAT_NORMAL)

 	{

 		return form("ds:%s", str);

 	}

 	else

 	{

 		return str;

 	}

 }