Let’s build our own TriCore de-assembler for AURIX™ - STEP6

in data

One standard feature is showing the current instruction de-assembly.

Such could be achieved in two ways:

  1. By parser the project code ELF file
  2. By decoding the instruction that is under execution during in the selected CPU

Definitely the second approach is more flexible since it could be performed even without the source codes and fitting to my purpose: reverse engineering.

Therefore, I decide to implement my own de-assembler for TriCore™ processor. Let me try to explain what has to be done. Let's take the ABS instruction (source TC1.6 - page 49):

where is clear that the instruction opcode for ABS is x1Cxxx0Bh. Therefore in my AURIXdebugger I will implement a structure like this:

{0x01C00B, 32, "ABS", "absolute Value", "ABS D[c], D[b] ", "Put the absolute value of data register D[b] in data register D[c]"}

where:

typedef struct deASM_n

{

    uint32_t uiOpCode; // Opcode (e.g. 0xDC for 'ji')

    uint8_t uiOpCodeLengh; // Lenght of the opcode (e.g. 16)

char sInStr[INSTSTRSIZE]; // Instruction Mnemonic

char sLongName[DESCSRSIZE]; // Instruction Longname

char sSyntax[DESCSRSIZE]; // Instruction Syntax

char sLDescr[DESCLRSIZE]; // Instruction long description

} deASM_t;

Easy, isn't it? (The only problem is to compile such structure for all opcodes that TriCore™ has!!!).

Having such structure (also if not for all opcodes) permit to write the function that decode and verbose the last executed instruction, as:

// Mnemonic Opcode Identification
void GetInstructionMnemonic(uint32_t uiInstruction)
{
bool bFoud=false;
uint32_t uiOpcode = uiInstruction & 0xFF; // isolate the opcode byte
int i=0;

for (int i=0; ( (i<NUMOPCODES) && !bFoud); i++)
{
if ( (uiOpcode == tc16[i].uiOpCode) && (uiInstruction&tc16[i].uiOpCode) == tc16[i].uiOpCode)
{
bFoud = true;
printf("(%s - %s - %s)", tc16[i].sInStr, tc16[i].sLongName, tc16[i].sSyntax);
break;
}
}
if (!bFoud)
printf("[Opcode not known - file 'Tricore1_6.h' need to be extended]");
}


Commenti

Posta un commento