ref: 7a145e89b301a1865661f7a6e60a21731f12824f
dir: /sys/src/9/xen/l.s/
#include "xendefs.h" #include "mem.h" /* * Some machine instructions not handled by 8[al]. */ #define OP16 BYTE $0x66 #define DELAY BYTE $0xEB; BYTE $0x00 /* JMP .+2 */ #define CPUID BYTE $0x0F; BYTE $0xA2 /* CPUID, argument in AX */ #define WRMSR BYTE $0x0F; BYTE $0x30 /* WRMSR, argument in AX/DX (lo/hi) */ #define RDTSC BYTE $0x0F; BYTE $0x31 /* RDTSC, result in AX/DX (lo/hi) */ #define RDMSR BYTE $0x0F; BYTE $0x32 /* RDMSR, result in AX/DX (lo/hi) */ #define HLT BYTE $0xF4 #define BSFL BYTE $0xf; BYTE $0xbc; BYTE $0xc0 /* bsfl AX,AX */ /* * Macros for calculating offsets within the page directory base * and page tables. Note that these are assembler-specific hence * the '<<2'. */ #define PDO(a) (((((a))>>22) & 0x03FF)<<2) #define PTO(a) (((((a))>>12) & 0x03FF)<<2) /* * Entry point from XEN's "linux" builder. * At this point RAM from 0..4M ("physical") is mapped at KZERO, * the kernel is loaded, we're running on a boot stack and a * boot page table. The start_info structure describes the * situation, and is pointed to by SI. * The stack is the highest used address. */ TEXT _start(SB), $0 MOVL SP, xentop(SB) /* set global for top of mapped region */ MOVL SI, xenstart(SB) /* set global to start_info_t */ MOVL $0, AX /* clear EFLAGS */ PUSHL AX POPFL CALL mmumapcpu0(SB) /* make mapping before using stack */ MOVL $(MACHADDR+MACHSIZE-4), SP /* set stack */ CALL main(SB) /* * Park a processor. Should never fall through a return from main to here, * should only be called by application processors when shutting down. */ TEXT idle(SB), $0 _idle: STI HLT JMP _idle /* * Read/write various system registers. * CR4 and the 'model specific registers' should only be read/written * after it has been determined the processor supports them */ TEXT _cycles(SB), $0 /* time stamp counter; cycles since power up */ RDTSC MOVL vlong+0(FP), CX /* &vlong */ MOVL AX, 0(CX) /* lo */ MOVL DX, 4(CX) /* hi */ RET TEXT rdmsr(SB), $0 /* model-specific register */ MOVL index+0(FP), CX RDMSR MOVL vlong+4(FP), CX /* &vlong */ MOVL AX, 0(CX) /* lo */ MOVL DX, 4(CX) /* hi */ RET /* Xen doesn't let us do this */ TEXT wrmsr(SB), $0 MOVL $-1, AX RET /* * Try to determine the CPU type which requires fiddling with EFLAGS. * If the Id bit can be toggled then the CPUID instruction can be used * to determine CPU identity and features. First have to check if it's * a 386 (Ac bit can't be set). If it's not a 386 and the Id bit can't be * toggled then it's an older 486 of some kind. * * cpuid(fun, regs[4]); */ TEXT cpuid(SB), $0 MOVL $0x240000, AX PUSHL AX POPFL /* set Id|Ac */ PUSHFL POPL BX /* retrieve value */ MOVL $0, AX PUSHL AX POPFL /* clear Id|Ac, EFLAGS initialised */ PUSHFL POPL AX /* retrieve value */ XORL BX, AX TESTL $0x040000, AX /* Ac */ JZ _cpu386 /* can't set this bit on 386 */ TESTL $0x200000, AX /* Id */ JZ _cpu486 /* can't toggle this bit on some 486 */ MOVL fn+0(FP), AX CPUID JMP _cpuid _cpu486: MOVL $0x400, AX JMP _maybezapax _cpu386: MOVL $0x300, AX _maybezapax: CMPL fn+0(FP), $1 JE _zaprest XORL AX, AX _zaprest: XORL BX, BX XORL CX, CX XORL DX, DX _cpuid: MOVL regs+4(FP), BP MOVL AX, 0(BP) MOVL BX, 4(BP) MOVL CX, 8(BP) MOVL DX, 12(BP) RET /* * Floating point. * Note: the encodings for the FCLEX, FINIT, FSAVE, FSTCW, FSENV and FSTSW * instructions do NOT have the WAIT prefix byte (i.e. they act like their * FNxxx variations) so WAIT instructions must be explicitly placed in the * code as necessary. */ #define FPOFF(l) ;\ MOVL CR0, AX ;\ ANDL $0xC, AX /* EM, TS */ ;\ CMPL AX, $0x8 ;\ JEQ l ;\ WAIT ;\ l: ;\ MOVL CR0, AX ;\ ANDL $~0x4, AX /* EM=0 */ ;\ ORL $0x28, AX /* NE=1, TS=1 */ ;\ MOVL AX, CR0 #define FPON ;\ MOVL CR0, AX ;\ ANDL $~0xC, AX /* EM=0, TS=0 */ ;\ MOVL AX, CR0 TEXT fpoff(SB), $0 /* disable */ FPOFF(l1) RET TEXT fpinit(SB), $0 /* enable and init */ FPON FINIT WAIT /* setfcr(FPPDBL|FPRNR|FPINVAL|FPZDIV|FPOVFL) */ /* note that low 6 bits are masks, not enables, on this chip */ PUSHW $0x0232 FLDCW 0(SP) POPW AX WAIT RET TEXT fpx87save(SB), $0 /* save state and disable */ MOVL p+0(FP), AX FSAVE 0(AX) /* no WAIT */ FPOFF(l2) RET TEXT fpx87restore(SB), $0 /* enable and restore state */ FPON MOVL p+0(FP), AX FRSTOR 0(AX) WAIT RET TEXT fpstatus(SB), $0 /* get floating point status */ FSTSW AX RET TEXT fpenv(SB), $0 /* save state without waiting */ MOVL p+0(FP), AX FSTENV 0(AX) RET TEXT fpclear(SB), $0 /* clear pending exceptions */ FPON FCLEX /* no WAIT */ FPOFF(l3) RET /* * Test-And-Set */ TEXT tas(SB), $0 TEXT _tas(SB), $0 MOVL $0xDEADDEAD, AX MOVL lock+0(FP), BX XCHGL AX, (BX) /* lock->key */ RET TEXT getstack(SB), $0 MOVL SP, AX RET TEXT mb386(SB), $0 POPL AX /* return PC */ PUSHFL PUSHL CS PUSHL AX IRETL TEXT mb586(SB), $0 XORL AX, AX CPUID RET TEXT sfence(SB), $0 BYTE $0x0f BYTE $0xae BYTE $0xf8 RET TEXT lfence(SB), $0 BYTE $0x0f BYTE $0xae BYTE $0xe8 RET TEXT mfence(SB), $0 BYTE $0x0f BYTE $0xae BYTE $0xf0 RET TEXT xchgw(SB), $0 MOVL v+4(FP), AX MOVL p+0(FP), BX XCHGW AX, (BX) RET TEXT xchgb(SB), $0 MOVL v+4(FP), AX MOVL p+0(FP), BX XCHGB AX, (BX) RET TEXT xchgl(SB), $0 MOVL v+4(FP), AX MOVL p+0(FP), BX XCHGL AX, (BX) RET /* Return the position of the first bit set. Undefined if zero. */ TEXT ffs(SB), $0 MOVL v+0(FP), AX BSFL RET TEXT cmpswap486(SB), $0 MOVL addr+0(FP), BX MOVL old+4(FP), AX MOVL new+8(FP), CX LOCK BYTE $0x0F; BYTE $0xB1; BYTE $0x0B /* CMPXCHGL CX, (BX) */ JNZ didnt MOVL $1, AX RET didnt: XORL AX,AX RET TEXT mul64fract(SB), $0 MOVL r+0(FP), CX XORL BX, BX /* BX = 0 */ MOVL a+8(FP), AX MULL b+16(FP) /* a1*b1 */ MOVL AX, 4(CX) /* r2 = lo(a1*b1) */ MOVL a+8(FP), AX MULL b+12(FP) /* a1*b0 */ MOVL AX, 0(CX) /* r1 = lo(a1*b0) */ ADDL DX, 4(CX) /* r2 += hi(a1*b0) */ MOVL a+4(FP), AX MULL b+16(FP) /* a0*b1 */ ADDL AX, 0(CX) /* r1 += lo(a0*b1) */ ADCL DX, 4(CX) /* r2 += hi(a0*b1) + carry */ MOVL a+4(FP), AX MULL b+12(FP) /* a0*b0 */ ADDL DX, 0(CX) /* r1 += hi(a0*b0) */ ADCL BX, 4(CX) /* r2 += carry */ RET /* * label consists of a stack pointer and a PC */ TEXT gotolabel(SB), $0 MOVL label+0(FP), AX MOVL 0(AX), SP /* restore sp */ MOVL 4(AX), AX /* put return pc on the stack */ MOVL AX, 0(SP) MOVL $1, AX /* return 1 */ RET TEXT setlabel(SB), $0 MOVL label+0(FP), AX MOVL SP, 0(AX) /* store sp */ MOVL 0(SP), BX /* store return pc */ MOVL BX, 4(AX) MOVL $0, AX /* return 0 */ RET TEXT mwait(SB), $0 MOVL addr+0(FP), AX MOVL (AX), CX ORL CX, CX JNZ _mwaitdone XORL DX, DX BYTE $0x0f; BYTE $0x01; BYTE $0xc8 /* MONITOR */ MOVL (AX), CX ORL CX, CX JNZ _mwaitdone XORL AX, AX BYTE $0x0f; BYTE $0x01; BYTE $0xc9 /* MWAIT */ _mwaitdone: RET /* * Interrupt/exception handling. * Each entry in the vector table calls either _strayintr or _strayintrx depending * on whether an error code has been automatically pushed onto the stack * (_strayintrx) or not, in which case a dummy entry must be pushed before retrieving * the trap type from the vector table entry and placing it on the stack as part * of the Ureg structure. * Exceptions to this are the syscall vector and the page fault * vector. Syscalls are dispatched seperately. Page faults * have to take care of the extra cr2 parameter that xen places * at the top of the stack. * The size of each entry in the vector table (6 bytes) is known in trapinit(). */ TEXT _strayintr(SB), $0 PUSHL AX /* save AX */ MOVL 4(SP), AX /* return PC from vectortable(SB) */ JMP intrcommon TEXT _strayintrx(SB), $0 XCHGL AX, (SP) /* swap AX with vectortable CALL PC */ intrcommon: PUSHL DS /* save DS */ PUSHL $(KDSEL) POPL DS /* fix up DS */ MOVBLZX (AX), AX /* trap type -> AX */ XCHGL AX, 4(SP) /* exchange trap type with saved AX */ PUSHL ES /* save ES */ PUSHL $(KDSEL) POPL ES /* fix up ES */ PUSHL FS /* save the rest of the Ureg struct */ PUSHL GS PUSHAL PUSHL SP /* Ureg* argument to trap */ CALL trap(SB) TEXT forkret(SB), $0 POPL AX POPAL POPL GS POPL FS POPL ES POPL DS ADDL $8, SP /* pop error code and trap type */ IRETL TEXT vectortable(SB), $0 CALL _strayintr(SB); BYTE $0x00 /* divide error */ CALL _strayintr(SB); BYTE $0x01 /* debug exception */ CALL _strayintr(SB); BYTE $0x02 /* NMI interrupt */ CALL _strayintr(SB); BYTE $0x03 /* breakpoint */ CALL _strayintr(SB); BYTE $0x04 /* overflow */ CALL _strayintr(SB); BYTE $0x05 /* bound */ CALL _strayintr(SB); BYTE $0x06 /* invalid opcode */ CALL _strayintr(SB); BYTE $0x07 /* no coprocessor available */ CALL _strayintrx(SB); BYTE $0x08 /* double fault */ CALL _strayintr(SB); BYTE $0x09 /* coprocessor segment overflow */ CALL _strayintrx(SB); BYTE $0x0A /* invalid TSS */ CALL _strayintrx(SB); BYTE $0x0B /* segment not available */ CALL _strayintrx(SB); BYTE $0x0C /* stack exception */ CALL _strayintrx(SB); BYTE $0x0D /* general protection error */ CALL _strayintrx(SB); BYTE $0x0E /* page fault */ CALL _strayintr(SB); BYTE $0x0F /* */ CALL _strayintr(SB); BYTE $0x10 /* coprocessor error */ CALL _strayintrx(SB); BYTE $0x11 /* alignment check */ CALL _strayintr(SB); BYTE $0x12 /* machine check */ CALL _strayintr(SB); BYTE $0x13 CALL _strayintr(SB); BYTE $0x14 CALL _strayintr(SB); BYTE $0x15 CALL _strayintr(SB); BYTE $0x16 CALL _strayintr(SB); BYTE $0x17 CALL _strayintr(SB); BYTE $0x18 CALL _strayintr(SB); BYTE $0x19 CALL _strayintr(SB); BYTE $0x1A CALL _strayintr(SB); BYTE $0x1B CALL _strayintr(SB); BYTE $0x1C CALL _strayintr(SB); BYTE $0x1D CALL _strayintr(SB); BYTE $0x1E CALL _strayintr(SB); BYTE $0x1F CALL _strayintr(SB); BYTE $0x20 /* VectorLAPIC */ CALL _strayintr(SB); BYTE $0x21 CALL _strayintr(SB); BYTE $0x22 CALL _strayintr(SB); BYTE $0x23 CALL _strayintr(SB); BYTE $0x24 CALL _strayintr(SB); BYTE $0x25 CALL _strayintr(SB); BYTE $0x26 CALL _strayintr(SB); BYTE $0x27 CALL _strayintr(SB); BYTE $0x28 CALL _strayintr(SB); BYTE $0x29 CALL _strayintr(SB); BYTE $0x2A CALL _strayintr(SB); BYTE $0x2B CALL _strayintr(SB); BYTE $0x2C CALL _strayintr(SB); BYTE $0x2D CALL _strayintr(SB); BYTE $0x2E CALL _strayintr(SB); BYTE $0x2F CALL _strayintr(SB); BYTE $0x30 CALL _strayintr(SB); BYTE $0x31 CALL _strayintr(SB); BYTE $0x32 CALL _strayintr(SB); BYTE $0x33 CALL _strayintr(SB); BYTE $0x34 CALL _strayintr(SB); BYTE $0x35 CALL _strayintr(SB); BYTE $0x36 CALL _strayintr(SB); BYTE $0x37 CALL _strayintr(SB); BYTE $0x38 CALL _strayintr(SB); BYTE $0x39 CALL _strayintr(SB); BYTE $0x3A CALL _strayintr(SB); BYTE $0x3B CALL _strayintr(SB); BYTE $0x3C CALL _strayintr(SB); BYTE $0x3D CALL _strayintr(SB); BYTE $0x3E CALL _strayintr(SB); BYTE $0x3F CALL _syscallintr(SB); BYTE $0x40 /* VectorSYSCALL */ CALL _strayintr(SB); BYTE $0x41 CALL _strayintr(SB); BYTE $0x42 CALL _strayintr(SB); BYTE $0x43 CALL _strayintr(SB); BYTE $0x44 CALL _strayintr(SB); BYTE $0x45 CALL _strayintr(SB); BYTE $0x46 CALL _strayintr(SB); BYTE $0x47 CALL _strayintr(SB); BYTE $0x48 CALL _strayintr(SB); BYTE $0x49 CALL _strayintr(SB); BYTE $0x4A CALL _strayintr(SB); BYTE $0x4B CALL _strayintr(SB); BYTE $0x4C CALL _strayintr(SB); BYTE $0x4D CALL _strayintr(SB); BYTE $0x4E CALL _strayintr(SB); BYTE $0x4F CALL _strayintr(SB); BYTE $0x50 CALL _strayintr(SB); BYTE $0x51 CALL _strayintr(SB); BYTE $0x52 CALL _strayintr(SB); BYTE $0x53 CALL _strayintr(SB); BYTE $0x54 CALL _strayintr(SB); BYTE $0x55 CALL _strayintr(SB); BYTE $0x56 CALL _strayintr(SB); BYTE $0x57 CALL _strayintr(SB); BYTE $0x58 CALL _strayintr(SB); BYTE $0x59 CALL _strayintr(SB); BYTE $0x5A CALL _strayintr(SB); BYTE $0x5B CALL _strayintr(SB); BYTE $0x5C CALL _strayintr(SB); BYTE $0x5D CALL _strayintr(SB); BYTE $0x5E CALL _strayintr(SB); BYTE $0x5F CALL _strayintr(SB); BYTE $0x60 CALL _strayintr(SB); BYTE $0x61 CALL _strayintr(SB); BYTE $0x62 CALL _strayintr(SB); BYTE $0x63 CALL _strayintr(SB); BYTE $0x64 CALL _strayintr(SB); BYTE $0x65 CALL _strayintr(SB); BYTE $0x66 CALL _strayintr(SB); BYTE $0x67 CALL _strayintr(SB); BYTE $0x68 CALL _strayintr(SB); BYTE $0x69 CALL _strayintr(SB); BYTE $0x6A CALL _strayintr(SB); BYTE $0x6B CALL _strayintr(SB); BYTE $0x6C CALL _strayintr(SB); BYTE $0x6D CALL _strayintr(SB); BYTE $0x6E CALL _strayintr(SB); BYTE $0x6F CALL _strayintr(SB); BYTE $0x70 CALL _strayintr(SB); BYTE $0x71 CALL _strayintr(SB); BYTE $0x72 CALL _strayintr(SB); BYTE $0x73 CALL _strayintr(SB); BYTE $0x74 CALL _strayintr(SB); BYTE $0x75 CALL _strayintr(SB); BYTE $0x76 CALL _strayintr(SB); BYTE $0x77 CALL _strayintr(SB); BYTE $0x78 CALL _strayintr(SB); BYTE $0x79 CALL _strayintr(SB); BYTE $0x7A CALL _strayintr(SB); BYTE $0x7B CALL _strayintr(SB); BYTE $0x7C CALL _strayintr(SB); BYTE $0x7D CALL _strayintr(SB); BYTE $0x7E CALL _strayintr(SB); BYTE $0x7F CALL _strayintr(SB); BYTE $0x80 /* Vector[A]PIC */ CALL _strayintr(SB); BYTE $0x81 CALL _strayintr(SB); BYTE $0x82 CALL _strayintr(SB); BYTE $0x83 CALL _strayintr(SB); BYTE $0x84 CALL _strayintr(SB); BYTE $0x85 CALL _strayintr(SB); BYTE $0x86 CALL _strayintr(SB); BYTE $0x87 CALL _strayintr(SB); BYTE $0x88 CALL _strayintr(SB); BYTE $0x89 CALL _strayintr(SB); BYTE $0x8A CALL _strayintr(SB); BYTE $0x8B CALL _strayintr(SB); BYTE $0x8C CALL _strayintr(SB); BYTE $0x8D CALL _strayintr(SB); BYTE $0x8E CALL _strayintr(SB); BYTE $0x8F CALL _strayintr(SB); BYTE $0x90 CALL _strayintr(SB); BYTE $0x91 CALL _strayintr(SB); BYTE $0x92 CALL _strayintr(SB); BYTE $0x93 CALL _strayintr(SB); BYTE $0x94 CALL _strayintr(SB); BYTE $0x95 CALL _strayintr(SB); BYTE $0x96 CALL _strayintr(SB); BYTE $0x97 CALL _strayintr(SB); BYTE $0x98 CALL _strayintr(SB); BYTE $0x99 CALL _strayintr(SB); BYTE $0x9A CALL _strayintr(SB); BYTE $0x9B CALL _strayintr(SB); BYTE $0x9C CALL _strayintr(SB); BYTE $0x9D CALL _strayintr(SB); BYTE $0x9E CALL _strayintr(SB); BYTE $0x9F CALL _strayintr(SB); BYTE $0xA0 CALL _strayintr(SB); BYTE $0xA1 CALL _strayintr(SB); BYTE $0xA2 CALL _strayintr(SB); BYTE $0xA3 CALL _strayintr(SB); BYTE $0xA4 CALL _strayintr(SB); BYTE $0xA5 CALL _strayintr(SB); BYTE $0xA6 CALL _strayintr(SB); BYTE $0xA7 CALL _strayintr(SB); BYTE $0xA8 CALL _strayintr(SB); BYTE $0xA9 CALL _strayintr(SB); BYTE $0xAA CALL _strayintr(SB); BYTE $0xAB CALL _strayintr(SB); BYTE $0xAC CALL _strayintr(SB); BYTE $0xAD CALL _strayintr(SB); BYTE $0xAE CALL _strayintr(SB); BYTE $0xAF CALL _strayintr(SB); BYTE $0xB0 CALL _strayintr(SB); BYTE $0xB1 CALL _strayintr(SB); BYTE $0xB2 CALL _strayintr(SB); BYTE $0xB3 CALL _strayintr(SB); BYTE $0xB4 CALL _strayintr(SB); BYTE $0xB5 CALL _strayintr(SB); BYTE $0xB6 CALL _strayintr(SB); BYTE $0xB7 CALL _strayintr(SB); BYTE $0xB8 CALL _strayintr(SB); BYTE $0xB9 CALL _strayintr(SB); BYTE $0xBA CALL _strayintr(SB); BYTE $0xBB CALL _strayintr(SB); BYTE $0xBC CALL _strayintr(SB); BYTE $0xBD CALL _strayintr(SB); BYTE $0xBE CALL _strayintr(SB); BYTE $0xBF CALL _strayintr(SB); BYTE $0xC0 CALL _strayintr(SB); BYTE $0xC1 CALL _strayintr(SB); BYTE $0xC2 CALL _strayintr(SB); BYTE $0xC3 CALL _strayintr(SB); BYTE $0xC4 CALL _strayintr(SB); BYTE $0xC5 CALL _strayintr(SB); BYTE $0xC6 CALL _strayintr(SB); BYTE $0xC7 CALL _strayintr(SB); BYTE $0xC8 CALL _strayintr(SB); BYTE $0xC9 CALL _strayintr(SB); BYTE $0xCA CALL _strayintr(SB); BYTE $0xCB CALL _strayintr(SB); BYTE $0xCC CALL _strayintr(SB); BYTE $0xCD CALL _strayintr(SB); BYTE $0xCE CALL _strayintr(SB); BYTE $0xCF CALL _strayintr(SB); BYTE $0xD0 CALL _strayintr(SB); BYTE $0xD1 CALL _strayintr(SB); BYTE $0xD2 CALL _strayintr(SB); BYTE $0xD3 CALL _strayintr(SB); BYTE $0xD4 CALL _strayintr(SB); BYTE $0xD5 CALL _strayintr(SB); BYTE $0xD6 CALL _strayintr(SB); BYTE $0xD7 CALL _strayintr(SB); BYTE $0xD8 CALL _strayintr(SB); BYTE $0xD9 CALL _strayintr(SB); BYTE $0xDA CALL _strayintr(SB); BYTE $0xDB CALL _strayintr(SB); BYTE $0xDC CALL _strayintr(SB); BYTE $0xDD CALL _strayintr(SB); BYTE $0xDE CALL _strayintr(SB); BYTE $0xDF CALL _strayintr(SB); BYTE $0xE0 CALL _strayintr(SB); BYTE $0xE1 CALL _strayintr(SB); BYTE $0xE2 CALL _strayintr(SB); BYTE $0xE3 CALL _strayintr(SB); BYTE $0xE4 CALL _strayintr(SB); BYTE $0xE5 CALL _strayintr(SB); BYTE $0xE6 CALL _strayintr(SB); BYTE $0xE7 CALL _strayintr(SB); BYTE $0xE8 CALL _strayintr(SB); BYTE $0xE9 CALL _strayintr(SB); BYTE $0xEA CALL _strayintr(SB); BYTE $0xEB CALL _strayintr(SB); BYTE $0xEC CALL _strayintr(SB); BYTE $0xED CALL _strayintr(SB); BYTE $0xEE CALL _strayintr(SB); BYTE $0xEF CALL _strayintr(SB); BYTE $0xF0 CALL _strayintr(SB); BYTE $0xF1 CALL _strayintr(SB); BYTE $0xF2 CALL _strayintr(SB); BYTE $0xF3 CALL _strayintr(SB); BYTE $0xF4 CALL _strayintr(SB); BYTE $0xF5 CALL _strayintr(SB); BYTE $0xF6 CALL _strayintr(SB); BYTE $0xF7 CALL _strayintr(SB); BYTE $0xF8 CALL _strayintr(SB); BYTE $0xF9 CALL _strayintr(SB); BYTE $0xFA CALL _strayintr(SB); BYTE $0xFB CALL _strayintr(SB); BYTE $0xFC CALL _strayintr(SB); BYTE $0xFD CALL _strayintr(SB); BYTE $0xFE CALL _strayintr(SB); BYTE $0xFF