diff --git a/Makefile b/Makefile
index 71ec0aa..8f69a24 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,8 @@ OBJS := $(DIR_BLD)/tests.o \
 	$(DIR_BLD)/core.o \
 	$(DIR_BLD)/console.o \
 	$(DIR_BLD)/string.o \
-	$(DIR_BLD)/convert.o
+	$(DIR_BLD)/convert.o \
+	$(DIR_BLD)/perror.o \
 OBJS_LST := false
 SRCS := $(patsubst $(DIR_BLD)/%.o,$(SRC_DIR)/%.asm,$(OBJS))
 
diff --git a/src/constants.asm b/src/constants.asm
index 5fe0666..db6763f 100644
--- a/src/constants.asm
+++ b/src/constants.asm
@@ -41,3 +41,139 @@ section .rodata
 	MAX_INT32		equ	0x7FFFFFFF
 	MAX_INT16		equ	0x7FFF
 	MAX_INT8		equ	0x7F
+
+	; System error codes
+	ENONE			equ	0
+	EPERM			equ	1
+	ENOENT			equ	2
+	ESRCH			equ	3
+	EINTR			equ	4
+	EIO			equ	5
+	ENXIO			equ	6
+	E2BIG			equ	7
+	ENOEXEC			equ	8
+	EBADF			equ	9
+	ECHILD			equ	10
+	EAGAIN			equ	11
+	ENOMEM			equ	12
+	EACCES			equ	13
+	EFAULT			equ	14
+	ENOTBLK			equ	15
+	EBUSY			equ	16
+	EEXIST			equ	17
+	EXDEV			equ	18
+	ENODEV			equ	19
+	ENOTDIR			equ	20
+	EISDIR			equ	21
+	EINVAL			equ	22
+	ENFILE			equ	23
+	EMFILE			equ	24
+	ENOTTY			equ	25
+	ETXTBSY			equ	26
+	EFBIG			equ	27
+	ENOSPC			equ	28
+	ESPIPE			equ	29
+	EROFS			equ	30
+	EMLINK			equ	31
+	EPIPE			equ	32
+	EDOM			equ	33
+	ERANGE			equ	34
+	EDEADLK			equ	35
+	ENAMETOOLONG		equ	36
+	ENOLCK			equ	37
+	ENOSYS			equ	38
+	ENOTEMPTY		equ	39
+	ELOOP			equ	40
+	EWOULDBLOCK		equ	EAGAIN
+	ENOMSG			equ	42
+	EIDRM			equ	43
+	ECHRNG			equ	44
+	EL2NSYNC		equ	45
+	EL3HLT			equ	46
+	EL3RST			equ	47
+	ELNRNG			equ	48
+	EUNATCH			equ	49
+	ENOCSI 			equ	50
+	EL2HLT			equ	51
+	EBADE			equ	52
+	EBADR			equ	53
+	EXFULL 			equ	54
+	ENOANO 			equ	55
+	EBADRQC 		equ	56
+	EBADSLT 		equ	57
+	EDEADLOCK 		equ	EDEADLK
+	EBFONT 			equ	59
+	ENOSTR 			equ	60
+	ENODATA 		equ	61
+	ETIME 			equ	62
+	ENOSR 			equ	63
+	ENONET 			equ	64
+	ENOPKG 			equ	65
+	EREMOTE 		equ	66
+	ENOLINK 		equ	67
+	EADV 			equ	68
+	ESRMNT 			equ	69
+	ECOMM 			equ	70
+	EPROTO 			equ	71
+	EMULTIHOP 		equ	72
+	EDOTDOT 		equ	73
+	EBADMSG 		equ	74
+	EOVERFLOW 		equ	75
+	ENOTUNIQ 		equ	76
+	EBADFD 			equ	77
+	EREMCHG 		equ	78
+	ELIBACC 		equ	79
+	ELIBBAD 		equ	80
+	ELIBSCN 		equ	81
+	ELIBMAX 		equ	82
+	ELIBEXEC 		equ	83
+	EILSEQ 			equ	84
+	ERESTART 		equ	85
+	ESTRPIPE 		equ	86
+	EUSERS 			equ	87
+	ENOTSOCK 		equ	88
+	EDESTADDRREQ 		equ	89
+	EMSGSIZE 		equ	90
+	EPROTOTYPE 		equ	91
+	ENOPROTOOPT 		equ	92
+	EPROTONOSUPPORT		equ	93
+	ESOCKTNOSUPPORT		equ	94
+	EOPNOTSUPP 		equ	95
+	EPFNOSUPPORT 		equ	96
+	EAFNOSUPPORT 		equ	97
+	EADDRINUSE 		equ	98
+	EADDRNOTAVAIL 		equ	99
+	ENETDOWN 		equ	100
+	ENETUNREACH 		equ	101
+	ENETRESET 		equ	102
+	ECONNABORTED 		equ	103
+	ECONNRESET 		equ	104
+	ENOBUFS 		equ	105
+	EISCONN 		equ	106
+	ENOTCONN 		equ	107
+	ESHUTDOWN 		equ	108
+	ETOOMANYREFS 		equ	109
+	ETIMEDOUT 		equ	110
+	ECONNREFUSED 		equ	111
+	EHOSTDOWN 		equ	112
+	EHOSTUNREACH 		equ	113
+	EALREADY 		equ	114
+	EINPROGRESS 		equ	115
+	ESTALE 			equ	116
+	EUCLEAN 		equ	117
+	ENOTNAM 		equ	118
+	ENAVAIL 		equ	119
+	EISNAM 			equ	120
+	EREMOTEIO 		equ	121
+	EDQUOT 			equ	122
+	ENOMEDIUM 		equ	123
+	EMEDIUMTYPE 		equ	124
+	ECANCELED 		equ	125
+	ENOKEY 			equ	126
+	EKEYEXPIRED 		equ	127
+	EKEYREVOKED 		equ	128
+	EKEYREJECTED 		equ	129
+	EOWNERDEAD 		equ	130
+	ENOTRECOVERABLE		equ	131
+	ERFKILL 		equ	132
+	EHWPOISON 		equ	133
diff --git a/src/perror.asm b/src/perror.asm
new file mode 100644
index 0000000..19b31c3
--- /dev/null
+++ b/src/perror.asm
@@ -0,0 +1,215 @@
+%include "src/constants.asm"
+
+extern	strlen
+
+section .rodata
+	errMsgs		dq	e0,e1,e2,e3,e4,e5,e6,e7,e8,e9,\
+				e10,e11,e12,e13,e14,e15,e16,e17,e18,e19,\
+				e20,e21,e22,e23,e24,e25,e26,e27,e28,e29,\
+				e30,e31,e32,e33,e34,e35,e36,e37,e38,e39,\
+				e40,e41,e42,e43,e44,e45,e46,e47,e48,e49,\
+				e50,e51,e52,e53,e54,e55,e56,e57,e58,e59,\
+				e60,e61,e62,e63,e64,e65,e66,e67,e68,e69,\
+				e70,e71,e72,e73,e74,e75,e76,e77,e78,e79,\
+				e80,e81,e82,e83,e84,e85,e86,e87,e88,e89,\
+				e90,e91,e92,e93,e94,e95,e96,e97,e98,e99,\
+				e100,e101,e102,e103,e104,e105,e106,e107,e108,e109,\
+				e110,e111,e112,e113,e114,e115,e116,e117,e118,e119,\
+				e120,e121,e122,e123,e124,e125,e126,e127,e128,e129,\
+				e130,e131,e132,e133
+	e0		db	"No error",NL,EOS
+	e1		db	"Operation not permitted",NL,EOS
+	e2		db	"No such file or directory",NL,EOS
+	e3		db	"No such process",NL,EOS
+	e4		db	"Interrupted system call",NL,EOS
+	e5		db	"I/O error",NL,EOS
+	e6		db	"No such device or address",NL,EOS
+	e7		db	"Argument list too long",NL,EOS
+	e8		db	"Exec format error",NL,EOS
+	e9		db	"Bad file number",NL,EOS
+	e10		db	"No child processes",NL,EOS
+	e11		db	"Try again",NL,EOS
+	e12		db	"Out of memory",NL,EOS
+	e13		db	"Permission denied",NL,EOS
+	e14		db	"Bad address",NL,EOS
+	e15		db	"Block device required",NL,EOS
+	e16		db	"Device or resource busy",NL,EOS
+	e17		db	"File exists",NL,EOS
+	e18		db	"Cross-device link",NL,EOS
+	e19		db	"No such device",NL,EOS
+	e20		db	"Not a directory",NL,EOS
+	e21		db	"Is a directory",NL,EOS
+	e22		db	"Invalid argument",NL,EOS
+	e23		db	"File table overflow",NL,EOS
+	e24		db	"Too many open files",NL,EOS
+	e25		db	"Not a typewriter",NL,EOS
+	e26		db	"Text file busy",NL,EOS
+	e27		db	"File too large",NL,EOS
+	e28		db	"No space left on device",NL,EOS
+	e29		db	"Illegal seek",NL,EOS
+	e30		db	"Read-only file system",NL,EOS
+	e31		db	"Too many links",NL,EOS
+	e32		db	"Broken pipe",NL,EOS
+	e33		db	"Math argument out of domain func",NL,EOS
+	e34		db	"Math result not representable",NL,EOS
+	e35		db	"Resource deadlock would occur",NL,EOS
+	e36		db	"File name too long",NL,EOS
+	e37		db	"No record locks available",NL,EOS
+	e38		db	"Invalid system call number",NL,EOS
+	e39		db	"Directory not empty",NL,EOS
+	e40		db	"Too many symbolic links encountered",NL,EOS
+	e41		equ	e11
+	e42		db	"No message of desired type",NL,EOS
+	e43		db	"Identifier removed",NL,EOS
+	e44		db	"Channel number out of range",NL,EOS
+	e45		db	"Level 2 not synchronized",NL,EOS
+	e46		db	"Level 3 halted",NL,EOS
+	e47		db	"Level 3 reset",NL,EOS
+	e48		db	"Link number out of range",NL,EOS
+	e49		db	"Protocol driver not attached",NL,EOS
+	e50		db	"No CSI structure available",NL,EOS
+	e51		db	"Level 2 halted",NL,EOS
+	e52		db	"Invalid exchange",NL,EOS
+	e53		db	"Invalid request descriptor",NL,EOS
+	e54		db	"Exchange full",NL,EOS
+	e55		db	"No anode",NL,EOS
+	e56		db	"Invalid request code",NL,EOS
+	e57		db	"Invalid slot",NL,EOS
+	e58		equ	e35	
+	e59		db	"Bad font file format",NL,EOS
+	e60		db	"Device not a stream",NL,EOS
+	e61		db	"No data available",NL,EOS
+	e62		db	"Timer expired",NL,EOS
+	e63		db	"Out of streams resources",NL,EOS
+	e64		db	"Machine is not on the network",NL,EOS
+	e65		db	"Package not installed",NL,EOS
+	e66		db	"Object is remote",NL,EOS
+	e67		db	"Link has been severed",NL,EOS
+	e68		db	"Advertise error",NL,EOS
+	e69		db	"Srmount error",NL,EOS
+	e70		db	"Communication error on send",NL,EOS
+	e71		db	"Protocol error",NL,EOS
+	e72		db	"Multihop attempted",NL,EOS
+	e73		db	"RFS specific error",NL,EOS
+	e74		db	"Not a data message",NL,EOS
+	e75		db	"Value too large for defined data type",NL,EOS
+	e76		db	"Name not unique on network",NL,EOS
+	e77		db	"File descriptor in bad state",NL,EOS
+	e78		db	"Remote address changed",NL,EOS
+	e79		db	"Can not acces a needed shared library",NL,EOS
+	e80		db	"Accessing a corrupted shared library",NL,EOS
+	e81		db	".lib section in a.out corrupted",NL,EOS
+	e82		db	"Attempting to link in too many shared libraries",NL,EOS
+	e83		db	"Cannot exec a shared library directly",NL,EOS
+	e84		db	"Illegal byte sequence",NL,EOS
+	e85		db	"Interrupted system call should be restarted",NL,EOS
+	e86		db	"Streams pip error",NL,EOS
+	e87		db	"Too many users",NL,EOS
+	e88		db	"Socket operation on non-socket",NL,EOS
+	e89		db	"Destination address required",NL,EOS
+	e90		db	"Message too long",NL,EOS
+	e91		db	"Protocol wrong type for socket",NL,EOS
+	e92		db	"Protocol not available",NL,EOS
+	e93		db	"Protocol not supported",NL,EOS
+	e94		db	"Socket type not supported",NL,EOS
+	e95		db	"Operation not supported on transport endpoint",NL,EOS
+	e96		db	"Protocol family not supported",NL,EOS
+	e97		db	"Address family not supported by protocol",NL,EOS
+	e98		db	"Address already in use",NL,EOS
+	e99		db	"Cannot assign requested address",NL,EOS
+	e100		db	"Network is down",NL,EOS
+	e101		db	"Network is unreachable",NL,EOS
+	e102		db	"Network dropped connection because of reset",NL,EOS
+	e103		db	"Software caused connection abort",NL,EOS
+	e104		db	"Connection reset by peer",NL,EOS
+	e105		db	"No buffer space available",NL,EOS
+	e106		db	"Transport endpoint is already connected",NL,EOS
+	e107		db	"Transport endpoint is not connected",NL,EOS
+	e108		db	"Cannot send after transport endpoint shutdown",NL,EOS
+	e109		db	"Too many references: cannot splice",NL,EOS
+	e110		db	"Connection timed out",NL,EOS
+	e111		db	"Connection refused",NL,EOS
+	e112		db	"Host is down",NL,EOS
+	e113		db	"No route to host",NL,EOS
+	e114		db	"Operation already in progress",NL,EOS
+	e115		db	"Operation now in progress",NL,EOS
+	e116		db	"Stale file handle",NL,EOS
+	e117		db	"Structure needs cleaning",NL,EOS
+	e118		db	"Not a XENIX named type file",NL,EOS
+	e119		db	"No XENIX semaphores available",NL,EOS
+	e120		db	"Is a named type file",NL,EOS
+	e121		db	"Remote I/O error",NL,EOS
+	e122		db	"Quota exceeded",NL,EOS
+	e123		db	"No medium found",NL,EOS
+	e124		db	"Wrong medium type",NL,EOS
+	e125		db	"Operation Canceled",NL,EOS
+	e126		db	"Required key not available",NL,EOS
+	e127		db	"Key has expired",NL,EOS
+	e128		db	"Key has been revoked",NL,EOS
+	e129		db	"Key was rejected by service",NL,EOS
+	e130		db	"Owner died",NL,EOS
+	e131		db	"State not recoverable",NL,EOS
+	e132		db	"Operation not possible due to RF-kill",NL,EOS
+	e133		db	"Memory page has hardware error",NL,EOS
+
+	unknownError	db	"Unknown error",NL,EOS
+	errMsgUser	db	": ",EOS
+
+section .text
+	global	perror
+
+;----- perror(*str[]) -----;
+; Prints a descriptive error to stderr.
+; Return value: N/A (current error code untouched)
+; Used registers:
+;	rax	Current error code (may be both positive or negative)
+;	rdi*	(arg) Pointer to str[] or 0 (no custom message)
+;	rdx*	Used for syscall NR_write
+;	r8*	(Re)stores pointer to str[]// Stores address of errMsgUser for cmov
+;	r9*	(Re)stores error code 
+;	r10*	(Re)stores pointer to error msg
+perror:
+	test	rax, rax
+	jz	.quit
+	js	.negErr
+	jmp	.cnt
+	.negErr:
+	neg	rax
+
+	.cnt:
+	mov	r9, rax
+
+	test	rdi, rdi
+	jz	.noUserMsg
+	mov	r8, rdi
+	call	strlen
+	mov	rdx, rax
+	mov	rax, NR_write
+	mov	rdi, FD_stderr
+	mov	rsi, r8
+	syscall
+	mov	rax, NR_write
+	mov	rdi, FD_stderr
+	lea	rsi, [rel errMsgUser]
+	mov	rdx, 2
+	syscall
+	mov	rax, r8
+	.noUserMsg:
+	cmp	r9, 133
+	ja	.invalidErr
+	lea	r10, [errMsgs + r9 * SIZE_QWORD]
+	mov	r10, [r10]
+	jmp	.printErrMsg
+	.invalidErr:
+	lea	r10, [rel unknownError]
+	.printErrMsg:
+	mov	rdi, r10
+	call	strlen
+	mov	rdx, rax
+	mov	rax, NR_write
+	mov	rdi, FD_stderr
+	mov	rsi, r10
+	syscall
+	.quit:
+	mov	rax, r9
+	ret