Menu
I am writing to a stdout in assembly language using sys_write system call and I want to print an error message if an error happens during write and then exit gracefully.
I am only able to exit but cant print error message using errno and perror. Any suggestions how to do handle the error if syscall fails. I want to print error message depending on the type of error that happened.
I am on Ubuntu 14.04 and I am using nasm to compile my assembly code.
Currently I am doing only this:
test rax,rax ; Lets make sure the file descriptor is valid
js skipWrite ;
872
Your program can use the strerror() and perror() functions to print the value of errno. The strerror() function returns a pointer to an error message string that is associated with errno. The perror() function prints a message to stderr.
errno is a preprocessor macro used for error indication. It expands to a static (until C++11) thread-local (since C++11) modifiable lvalue of type int. Several standard library functions indicate errors by writing positive integers to errno .
" A value of 0 indicates that there is no error in the program." and "As a good practice, developer should set errno to 0 at the time of initialization of the program" By convention we check the errno variable only when there is an error occurred (like some of the function returned with -1).
perror and errno are only available if you link against the libc (-lc).
A "naked" syscall (without library support) usually returns in case of failure "the negative of a standard error code" (man syscall(2)). With a simple NEG you get the positive number of the error.
The error numbers can be found in the Linux source-files include/asm-generic/errno-base.h and include/asm-generic/errno.h.
The possible errors are described in the man-pages, e.g. man open(2). The name of a specific syscall can be figured out (with a bit of imagination) here. strace on programs that are known to work can be helpful.
I wrote an example showing how to build a list of "Pascal"-strings with the error messages and how to walk through that list:
DEFAULT rel
GLOBAL _start
SECTION .data
non_existing_file db "bielefeld.txt",0
SECTION .text
_start:
push rbp
mov rbp, rsp
and rsp, -16 ; Align 16
mov rdi, non_existing_file ; Pointer to null-terminated filename
xor rsi, rsi ; RD_ONLY
mov rax, 2 ; sys_open
syscall ; Call Linux
; if no errorcode (EAX > -1 || EAX < -133) exit (and close)
cmp eax, -1
jg .done
cmp eax, -133
jl .done
neg rax ; Get positive error number: RAX = Abs (RAX)
mov rdi, rax ; Argument for my_perror
call my_perror ; Output error message
.done:
leave
xor edi, edi ; Return 0
mov eax, 60 ; sys_exit
syscall
;==================== my_perror ====================
SECTION .text
my_perror: ; ARG: RDI=errno
push rbp
mov rbp, rsp
sub rsp, 16 ; Aligning 16 though only one byte is needed
; No processing if wrong number
test edi, edi
jz .done
cmp edi, 133
ja .done
; Walk through the err_txt-list
xor edx,edx
mov rsi, err_txt
.L1:
lea rsi, [rsi+rdx]
mov dl, [rsi] ; Length of string
add rsi, 1 ; Pointer to string
sub edi, 1
jnz .L1
mov edi, 1 ; stdout
mov eax, 1 ; sys_write
syscall ; call Linux
mov byte [rsp], 0x0A ; Linefeed
mov rsi, rsp
mov edx, 1
mov edi, 1 ; stdout
mov eax, 1 ; sys_write
syscall ; call Linux
.done:
leave
ret
SECTION .data
%MACRO DATA_ERR 1
%strlen len %1
db len, %1
%ENDMACRO
err_txt:
; /usr/src/linux-source-3.2/include/asm-generic/errno-base.h
DATA_ERR "Operation not permitted" ; EPERM 1
DATA_ERR "No such file or directory" ; ENOENT 2
DATA_ERR "No such process" ; ESRCH 3
DATA_ERR "Interrupted system call" ; EINTR 4
DATA_ERR "I/O error" ; EIO 5
DATA_ERR "No such device or address" ; ENXIO 6
DATA_ERR "Argument list too long" ; E2BIG 7
DATA_ERR "Exec format error" ; ENOEXEC 8
DATA_ERR "Bad file number" ; EBADF 9
DATA_ERR "No child processes" ; ECHILD 10
DATA_ERR "Try again" ; EAGAIN 11
DATA_ERR "Out of memory" ; ENOMEM 12
DATA_ERR "Permission denied" ; EACCES 13
DATA_ERR "Bad address" ; EFAULT 14
DATA_ERR "Block device required" ; ENOTBLK 15
DATA_ERR "Device or resource busy" ; EBUSY 16
DATA_ERR "File exists" ; EEXIST 17
DATA_ERR "Cross-device link" ; EXDEV 18
DATA_ERR "No such device" ; ENODEV 19
DATA_ERR "Not a directory" ; ENOTDIR 20
DATA_ERR "Is a directory" ; EISDIR 21
DATA_ERR "Invalid argument" ; EINVAL 22
DATA_ERR "File table overflow" ; ENFILE 23
DATA_ERR "Too many open files" ; EMFILE 24
DATA_ERR "Not a typewriter" ; ENOTTY 25
DATA_ERR "Text file busy" ; ETXTBSY 26
DATA_ERR "File too large" ; EFBIG 27
DATA_ERR "No space left on device" ; ENOSPC 28
DATA_ERR "Illegal seek" ; ESPIPE 29
DATA_ERR "Read-only file system" ; EROFS 30
DATA_ERR "Too many links" ; EMLINK 31
DATA_ERR "Broken pipe" ; EPIPE 32
DATA_ERR "Math argument out of domain of func" ; EDOM 33
DATA_ERR "Math result not representable" ; ERANGE 34
DATA_ERR "Resource deadlock would occur" ; EDEADLK 35
; /usr/src/linux-source-3.2/include/asm-generic/errno.h
DATA_ERR "File name too long" ; ENAMETOOLONG 36
DATA_ERR "No record locks available" ; ENOLCK 37
DATA_ERR "Function not implemented" ; ENOSYS 38
DATA_ERR "Directory not empty" ; ENOTEMPTY 39
DATA_ERR "Too many symbolic links encountered" ; ELOOP 40
DATA_ERR "Operation would block" ; EWOULDBLOCK EAGAIN
DATA_ERR "No message of desired type" ; ENOMSG 42
DATA_ERR "Identifier removed" ; EIDRM 43
DATA_ERR "Channel number out of range" ; ECHRNG 44
DATA_ERR "Level 2 not synchronized" ; EL2NSYNC 45
DATA_ERR "Level 3 halted" ; EL3HLT 46
DATA_ERR "Level 3 reset" ; EL3RST 47
DATA_ERR "Link number out of range" ; ELNRNG 48
DATA_ERR "Protocol driver not attached" ; EUNATCH 49
DATA_ERR "No CSI structure available" ; ENOCSI 50
DATA_ERR "Level 2 halted" ; EL2HLT 51
DATA_ERR "Invalid exchange" ; EBADE 52
DATA_ERR "Invalid request descriptor" ; EBADR 53
DATA_ERR "Exchange full" ; EXFULL 54
DATA_ERR "No anode" ; ENOANO 55
DATA_ERR "Invalid request code" ; EBADRQC 56
DATA_ERR "Invalid slot" ; EBADSLT 57
DATA_ERR "Resource deadlock would occur" ; EDEADLOCK EDEADLK
DATA_ERR "Bad font file format" ; EBFONT 59
DATA_ERR "Device not a stream" ; ENOSTR 60
DATA_ERR "No data available" ; ENODATA 61
DATA_ERR "Timer expired" ; ETIME 62
DATA_ERR "Out of streams resources" ; ENOSR 63
DATA_ERR "Machine is not on the network" ; ENONET 64
DATA_ERR "Package not installed" ; ENOPKG 65
DATA_ERR "Object is remote" ; EREMOTE 66
DATA_ERR "Link has been severed" ; ENOLINK 67
DATA_ERR "Advertise error" ; EADV 68
DATA_ERR "Srmount error" ; ESRMNT 69
DATA_ERR "Communication error on send" ; ECOMM 70
DATA_ERR "Protocol error" ; EPROTO 71
DATA_ERR "Multihop attempted" ; EMULTIHOP 72
DATA_ERR "RFS specific error" ; EDOTDOT 73
DATA_ERR "Not a data message" ; EBADMSG 74
DATA_ERR "Value too large for defined data type" ; EOVERFLOW 75
DATA_ERR "Name not unique on network" ; ENOTUNIQ 76
DATA_ERR "File descriptor in bad state" ; EBADFD 77
DATA_ERR "Remote address changed" ; EREMCHG 78
DATA_ERR "Can not access a needed shared library" ; ELIBACC 79
DATA_ERR "Accessing a corrupted shared library" ; ELIBBAD 80
DATA_ERR ".lib section in a.out corrupted" ; ELIBSCN 81
DATA_ERR "Attempting to link in too many shared libraries" ; ELIBMAX 82
DATA_ERR "Cannot exec a shared library directly" ; ELIBEXEC 83
DATA_ERR "Illegal byte sequence" ; EILSEQ 84
DATA_ERR "Interrupted system call should be restarted" ; ERESTART 85
DATA_ERR "Streams pipe error" ; ESTRPIPE 86
DATA_ERR "Too many users" ; EUSERS 87
DATA_ERR "Socket operation on non-socket" ; ENOTSOCK 88
DATA_ERR "Destination address required" ; EDESTADDRREQ 89
DATA_ERR "Message too long" ; EMSGSIZE 90
DATA_ERR "Protocol wrong type for socket" ; EPROTOTYPE 91
DATA_ERR "Protocol not available" ; ENOPROTOOPT 92
DATA_ERR "Protocol not supported" ; EPROTONOSUPPORT 93
DATA_ERR "Socket type not supported" ; ESOCKTNOSUPPORT 94
DATA_ERR "Operation not supported on transport endpoint" ; EOPNOTSUPP 95
DATA_ERR "Protocol family not supported" ; EPFNOSUPPORT 96
DATA_ERR "Address family not supported by protocol" ; EAFNOSUPPORT 97
DATA_ERR "Address already in use" ; EADDRINUSE 98
DATA_ERR "Cannot assign requested address" ; EADDRNOTAVAIL 99
DATA_ERR "Network is down" ; ENETDOWN 100
DATA_ERR "Network is unreachable" ; ENETUNREACH 101
DATA_ERR "Network dropped connection because of reset" ; ENETRESET 102
DATA_ERR "Software caused connection abort" ; ECONNABORTED 103
DATA_ERR "Connection reset by peer" ; ECONNRESET 104
DATA_ERR "No buffer space available" ; ENOBUFS 105
DATA_ERR "Transport endpoint is already connected" ; EISCONN 106
DATA_ERR "Transport endpoint is not connected" ; ENOTCONN 107
DATA_ERR "Cannot send after transport endpoint shutdown" ; ESHUTDOWN 108
DATA_ERR "Too many references: cannot splice" ; ETOOMANYREFS 109
DATA_ERR "Connection timed out" ; ETIMEDOUT 110
DATA_ERR "Connection refused" ; ECONNREFUSED 111
DATA_ERR "Host is down" ; EHOSTDOWN 112
DATA_ERR "No route to host" ; EHOSTUNREACH 113
DATA_ERR "Operation already in progress" ; EALREADY 114
DATA_ERR "Operation now in progress" ; EINPROGRESS 115
DATA_ERR "Stale NFS file handle" ; ESTALE 116
DATA_ERR "Structure needs cleaning" ; EUCLEAN 117
DATA_ERR "Not a XENIX named type file" ; ENOTNAM 118
DATA_ERR "No XENIX semaphores available" ; ENAVAIL 119
DATA_ERR "Is a named type file" ; EISNAM 120
DATA_ERR "Remote I/O error" ; EREMOTEIO 121
DATA_ERR "Quota exceeded" ; EDQUOT 122
DATA_ERR "No medium found" ; ENOMEDIUM 123
DATA_ERR "Wrong medium type" ; EMEDIUMTYPE 124
DATA_ERR "Operation Canceled" ; ECANCELED 125
DATA_ERR "Required key not available" ; ENOKEY 126
DATA_ERR "Key has expired" ; EKEYEXPIRED 127
DATA_ERR "Key has been revoked" ; EKEYREVOKED 128
DATA_ERR "Key was rejected by service" ; EKEYREJECTED 129
DATA_ERR "Owner died" ; EOWNERDEAD 130
DATA_ERR "State not recoverable" ; ENOTRECOVERABLE 131
DATA_ERR "Operation not possible due to RF-kill" ; ERFKILL 132
DATA_ERR "Memory page has hardware error" ; EHWPOISON 133
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
