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/*
Copyright (C) 2020-2021 Reiko Asakura. All Rights Reserved.
Moonshine
*/
#include <libdbg.h>
#include "opcode.h"
static int decode_bl_common(
uint16_t op_lo, uint16_t op_hi, int *imm,
uint16_t mask_lo, uint16_t chk_lo, uint16_t mask_hi, uint16_t chk_hi)
{
// verify the form
if ((op_lo & mask_lo) != chk_lo) {
SCE_DBG_LOG_ERROR("Low halfword check failed");
return -1;
}
if ((op_hi & mask_hi) != chk_hi) {
SCE_DBG_LOG_ERROR("High halfword check failed");
return -1;
}
// decode
int S = (op_lo & 0x0400) >> 10;
int J1 = (op_hi & 0x2000) >> 13;
int J2 = (op_hi & 0x0800) >> 11;
int I1 = ~(J1 ^ S) & 1;
int I2 = ~(J2 ^ S) & 1;
int imm10 = op_lo & 0x03FF;
int imm11 = op_hi & 0x07FF;
// combine to 25 bits and sign extend
*imm = (S << 31) | (I1 << 30) | (I2 << 29) | (imm10 << 19) | (imm11 << 8);
*imm >>= 7;
SCE_DBG_LOG_INFO("BL %04hX %04hX decoded with immediate 0x%08X", op_lo, op_hi, *imm);
return 0;
}
static int decode_blx_t2(uint16_t op_lo, uint16_t op_hi, int *imm) {
return decode_bl_common(op_lo, op_hi, imm, 0xF800, 0xF000, 0xD001, 0xC000);
}
int get_addr_blx(uint16_t *pc, uint16_t **addr) {
int ret;
int offset = 0;
if ((ret = decode_blx_t2(pc[0], pc[1], &offset)) < 0) {
return ret;
}
// PC is one word ahead and aligned backwards to word boundary
*addr = pc + 2 - ((uintptr_t)pc % 4 ? 1 : 0) + offset/2;
SCE_DBG_LOG_INFO("BLX at %p branches to %p", pc, *addr);
return 0;
}
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