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implement analyze of ModRM

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mykola2312 2024-08-16 13:31:58 +03:00
parent 64f44d9a44
commit 35e6628ec7
1 changed files with 55 additions and 0 deletions
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55
src/rtdisasm.c
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@ -133,6 +133,61 @@ static const instruction_t* find_instruction(const uint8_t* cur, unsigned type,
return NULL; return NULL;
} }
typedef struct {
uint8_t mod;
uint8_t rm;
uint8_t has_sib;
uint8_t disp_len;
} modrm_encoding_t;
static const modrm_encoding_t modrm_encodings[] = {
{ .mod = 0b00, .rm = 0b100, .has_sib = 1, .disp_len = 0 },
{ .mod = 0b00, .rm = 0b101, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b01, .rm = 0b000, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b001, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b010, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b011, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b100, .has_sib = 1, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b101, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b110, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b01, .rm = 0b111, .has_sib = 0, .disp_len = 1 },
{ .mod = 0b10, .rm = 0b000, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b001, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b010, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b011, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b100, .has_sib = 1, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b101, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b110, .has_sib = 0, .disp_len = 4 },
{ .mod = 0b10, .rm = 0b111, .has_sib = 0, .disp_len = 4 },
};
static const unsigned modrm_encodings_len = sizeof(modrm_encodings) / sizeof(modrm_encoding_t);
// analyze ModRM and determine if it employs SIB byte,
// as well as any displacements
static void analyzy_modrm(const uint8_t modrm, uint8_t* has_sib, uint8_t* disp_len)
{
const uint8_t mod = modrm >> 6;
const uint8_t rm = modrm & 0b111;
// default values
*has_sib = 0;
*disp_len = 0;
// now lets look up in table and if matches
// set proper values
for (unsigned i = 0; i < modrm_encodings_len; i++)
{
modrm_encoding_t* encoding = &modrm_encodings[i];
if (encoding->mod == mod && encoding->rm == rm)
{
*has_sib = encoding->has_sib;
*disp_len = encoding->disp_len;
}
}
}
int rtdisasm_analyze_single(const uint8_t* code, uint8_t size) int rtdisasm_analyze_single(const uint8_t* code, uint8_t size)
{ {
const uint8_t* cur = code; const uint8_t* cur = code;