Execute Brain****/x86 Assembly
x86_64 Assembly
GAS Syntax for Linux. Called it "Brainkrieg" after Teen Girl Squad. Operating principle is a little like a multi-cycle processor.
Implementation:
<lang>// Assembly brainf*** interpreter // Alternative name: "ASSembly brainF*** interpretER" // Compiles with `gcc -nostdlib brainkrieg.sx -o brainkrieg` // Usage: ./brainkrieg "filename" // Return 0 if normal exit
- define SYS_READ $0
- define SYS_WRITE $1
- define SYS_OPEN $2
- define SYS_CLOSE $3
- define SYS_FSTAT $5
- define SYS_MMAP $9
- define SYS_MUNMAP $11
- define SYS_EXIT $60
// From experiments:
- define FSIZEOFF 48
- define STATSIZE 144
// From Linux source:
- define RDONLY $00
- define PROT_READ $0x1
- define MAP_PRIVATE $0x02
- define STDIN $0
- define STDOUT $1
.global _start .text
.macro ERRCHECK code
cmpq $\code, %rax je fs_error
.endm
/* Local stack notes:
0: int fd
- /
- define STACKSIZE $4
_start:
/* Entry Point: */
// Open:
movq RDONLY, %rsi
// Filename ptr is on stack currently as argv[1]:
cmpq $1, (%rsp) // if argc is 1, error
jnz open_file
jmp fs_error
open_file:
movq 16(%rsp), %rdi // argc(8), argv0(8) => rsp+16. filename
movq SYS_OPEN, %rax
syscall
ERRCHECK -1
subq STACKSIZE, %rsp // local stack
movl %eax, (%rsp) // int fd = open(argv[1], RDONLY)
// fstat to get filesize
fstat:
movq $statstruct, %rsi
movl (%rsp), %edi // fd
movq SYS_FSTAT, %rax
syscall // fstat(fd, statstruct)
ERRCHECK -1
// mmap - don't forget to munmap.
mmap:
movq $0, %r9 // offset
movq (%rsp), %r8 // fd
movq MAP_PRIVATE, %r10
movq PROT_READ, %rdx
movq filesize, %rsi
movq (%rsp), %rdi // vmemptr
movq SYS_MMAP, %rax
syscall
ERRCHECK -1
// Set up machine:
boot:
movq %rax, head // head = mmap'd file start
movq %rax, inst_ptr // inst_ptr = head
addq filesize, %rax
movq %rax, end // end = head+filesize
movq $tape, data_ptr // data_ptr = tape
xorq %rax, %rax
/* Magic happens here:
- Fetch symbol
- Decode symbol
- Execute opcode
- Instruction out of range = halt
- Data out of range = halt
*/
OS_start:
fetch:
movq inst_ptr, %rbx
cmpq end, %rbx
ja shutdown // End of code
movb (%rbx), %al
incq %rbx
movq %rbx, inst_ptr
decode:
cmpb $'+, %al
je inc_data
cmpb $'-, %al
je dec_data
cmpb $'>, %al
je dp_right
cmpb $'<, %al
je dp_left
cmpb $'[, %al
je brf
cmpb $'], %al
je brb
cmpb $'., %al
je out_data
cmpb $',, %al
je in_data
jmp fetch
// execute:
dp_left:
cmpq $tape, data_ptr
jz scram
decq data_ptr
jmp fetch
dp_right:
cmpq $endtape, data_ptr
jz scram
incq data_ptr
jmp fetch
dec_data:
movq data_ptr, %rbx
decq (%rbx)
jmp fetch
inc_data:
movq data_ptr, %rbx
incq (%rbx)
jmp fetch
out_data:
movq $1, %rdx
movq data_ptr, %rsi
movq STDOUT, %rdi
movq SYS_WRITE, %rax
syscall
ERRCHECK -1
jmp fetch
in_data:
movq $1, %rdx
movq data_ptr, %rsi
movq STDIN, %rdi
movq SYS_READ, %rax
syscall
ERRCHECK -1
cmpb $'\n, (%rsi)
je fetch
movq %rax, junkChar
jmp fetch
brf: // branch if *dp=0
movq data_ptr, %rbx
cmpb $0, (%rbx)
jnz fetch
matchfwd:
movq inst_ptr, %rbx
movb (%rbx), %al
cmpb $'[, %al
jne no_smph
incq brack_smph
cmpq end, %rbx
je scram
incq inst_ptr
jmp matchfwd
no_smph: // no semaphore needed
cmpb $'], %al
je check_smph
cmpq end, %rbx
je scram
incq inst_ptr
jmp matchfwd
check_smph: // check if semaphore set
cmpq $0, brack_smph
jz donematch
decq brack_smph
cmpq end, %rbx
je scram
incq inst_ptr
jmp matchfwd
brb: // branch if *dp!=0
movq data_ptr, %rbx
cmpb $0, (%rbx)
jz fetch
subq $2, inst_ptr // Branch taken, scan back.
matchbwd:
movq inst_ptr, %rbx
movb (%rbx), %al
cmpb $'], %al
jne no_smph2
incq brack_smph
cmpq head, %rbx
je scram
decq inst_ptr
jmp matchbwd
no_smph2: // no semaphore needed
cmpb $'[, %al
je check_smph2
cmpq head, %rbx
je scram
decq inst_ptr
jmp matchbwd
check_smph2: // check if semaphore set
cmpq $0, brack_smph
jz donematch2
decq brack_smph
cmpq head, %rbx
je scram
decq inst_ptr
jmp matchbwd
donematch:
incq inst_ptr
donematch2:
jmp fetch
scram: // Memory breached
movq $0x7f, err_val
shutdown:
// Consume rest of stdin if we used it.
cmpb $0, junkChar
jz skip_flush
flush_stdin:
movq SYS_READ, %rax
movq STDIN, %rdi
movq $junkChar, %rsi
movq $1, %rdx
syscall
cmpq $0, %rax // EOF
jz skip_flush
cmpb $'\n, junkChar
jne flush_stdin
// munmap
skip_flush:
movq filesize, %rsi
movq head, %rdi
movq SYS_MUNMAP, %rax
syscall // munmap(vmemptr, filesize)
cmpq $-1, %rax
je fs_error
// close
movl (%rsp), %edi
movq SYS_CLOSE, %rax
syscall // close(fd)
ERRCHECK -1
exit:
movq SYS_EXIT, %rax movzbq err_val, %rdi syscall
fs_error:
movq SYS_EXIT, %rax movq $-1, %rdi syscall // exit(-1)
.data brack_smph: // Bracket matching semaphore
.quad 0
junkChar: // Also used to check if input was used.
.byte 0
err_val:
.byte 0
statstruct: // This struct is 144 bytes. Only want size (+48)
.zero FSIZEOFF filesize: // 8 bytes. .quad 0 .zero STATSIZE-FSIZEOFF+8
// Program: head:
.quad 0
end:
.quad 0
inst_ptr:
.quad 0
// Data: data_ptr:
.quad 0
tape:
.zero 30000
endtape:
.zero 1
</lang>