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Properly create BLX instruction #1266

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Jun 29, 2019
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Properly create BLX instruction #1266

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12 changes: 9 additions & 3 deletions arm9/source/patches.c
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Original file line number Diff line number Diff line change
Expand Up @@ -555,18 +555,24 @@ u32 patchP9AMTicketWrapperZeroKeyIV(u8 *pos, u32 size, u32 firmVersion)
static const u8 pattern[] = {0x20, 0x21, 0xA6, 0xA8};

u32 function = (u32)memsearch(pos, __rt_memclr_pattern, size, sizeof(__rt_memclr_pattern));
u32 *off = (u32 *)memsearch(pos, pattern, size, sizeof(pattern));
u16 *off = (u16 *)memsearch(pos, pattern, size, sizeof(pattern));

if(function == 0 || off == NULL) return firmVersion == 0xFFFFFFFF ? 0 : 1;

s32 opjumpdistance = (s32)(function - ((u32)&off[2])) / 2;
//After the found code it's a BL call (at &off[2]), that will be replaced
//From Thumb, op distance for setting in BLX can be got with,
//(Destination_offset - blx_op_offset+2) / 2
s32 opjumpdistance = (s32)(function - ((u32)&off[3])) / 2;

//Beyond limit
if(opjumpdistance < -0x1fffff || opjumpdistance > 0x1fffff) return 1;

//r0 and r1 for old call are already correct for this one
//BLX __rt_memclr
off[1] = 0xE800F000U | (((u32)opjumpdistance & 0x7FF) << 16) | (((u32)opjumpdistance >> 11) & 0x3FF) | (((u32)opjumpdistance >> 21) & 0x400);
u32 op = (0xE800F000U | (((u32)opjumpdistance & 0x7FF) << 16) | (((u32)opjumpdistance >> 11) & 0x3FF) | (((u32)opjumpdistance >> 21) & 0x400)) & ~(1<<16);

off[2] = op;
off[3] = op >> 16;

return 0;
}
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