diff options
Diffstat (limited to 'src/x86.c')
| -rw-r--r-- | src/x86.c | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/src/x86.c b/src/x86.c new file mode 100644 index 0000000..e33efbb --- /dev/null +++ b/src/x86.c @@ -0,0 +1,87 @@ +/* + * Copyright © 2022 Michael Smith <mikesmiffy128@gmail.com> + * + * Permission to use, copy, modify, and/or distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH + * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY + * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, + * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM + * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR + * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR + * PERFORMANCE OF THIS SOFTWARE. + */ + +#include "intdefs.h" +#include "x86.h" + +static int mrm(uchar b, int addrlen) { + // I won't lie: I don't *entirely* understand this particular logic. I + // largely based it on some public domain code I found on the internet + if (addrlen == 4 || b & 0xC0) { + int sib = addrlen == 4 && b < 0xC0 && (b & 7) == 4; + switch (b & 0xC0) { + // disp8 + case 0x40: return 2 + sib; + // disp16/32 + case 0: if ((b & 7) == 5) case 0x80: return 1 + addrlen + sib; + } + // disp8/32 + if (sib && (b & 7) == 5) return b & 0x40 ? 3 : 6; + } + if (addrlen == 2 && b == 0x26) return 3; + return 1; // NOTE: include the mrm itself in the byte count +} + +int x86_len(const void *insn_) { +#define CASES(name, _) case name: + const uchar *insn = insn_; + int pfxlen = 0, addrlen = 4, operandlen = 4; + +p: switch (*insn) { + case X86_PFX_ADSZ: addrlen = 2; goto P; // bit dumb sorry + case X86_PFX_OPSZ: operandlen = 2; +P: X86_SEG_PREFIXES(CASES) + case X86_PFX_LOCK: case X86_PFX_REPN: case X86_PFX_REP: + // instruction can only be 15 bytes. this could go over, oh well, + // just don't want to loop for 8 million years + if (++pfxlen == 14) return -1; + ++insn; + goto p; + } + + switch (*insn) { + X86_OPS_1BYTE_NO(CASES) return pfxlen + 1; + X86_OPS_1BYTE_I8(CASES) operandlen = 1; + X86_OPS_1BYTE_IW(CASES) return pfxlen + 1 + operandlen; + X86_OPS_1BYTE_I16(CASES) return pfxlen + 3; + X86_OPS_1BYTE_MRM(CASES) return pfxlen + 1 + mrm(insn[1], addrlen); + X86_OPS_1BYTE_MRM_I8(CASES) operandlen = 1; + X86_OPS_1BYTE_MRM_IW(CASES) + return pfxlen + 1 + operandlen + mrm(insn[1], addrlen); + case X86_ENTER: return pfxlen + 4; + case X86_CRAZY8: operandlen = 1; + case X86_CRAZYW: + if ((insn[1] & 0x38) >= 0x10) operandlen = 0; + return pfxlen + 2 + operandlen + mrm(insn[1], addrlen); + case X86_2BYTE: ++insn; goto b2; + } + return -1; + +b2: switch (*insn) { + // we don't support any 3 byte ops for now, implement if ever needed... + case X86_3BYTE1: case X86_3BYTE2: case X86_3DNOW: return -1; + X86_OPS_2BYTE_NO(CASES) return pfxlen + 2; + X86_OPS_2BYTE_IW(CASES) return pfxlen + 2 + operandlen; + X86_OPS_2BYTE_MRM(CASES) return pfxlen + 2 + mrm(insn[1], addrlen); + X86_OPS_2BYTE_MRM_I8(CASES) operandlen = 1; + return pfxlen + 2 + operandlen + mrm(insn[1], addrlen); + } + + return -1; +#undef CASES +} + +// vi: sw=4 ts=4 noet tw=80 cc=80 |