Show auxilary vectors (flat assembler)

showauvec.fasm

; Show Auxiliary Vectors (AT_*)
; compile:
; > fasm showauvec.fasm showauvec
; >> flat assembler  version 1.71.38  (16384 kilobytes memory)
; >> 3 passes, 1179 bytes.
; [email protected]
; see also http://articles.manugarg.com/aboutelfauxiliaryvectors
;   https://github.com/torvalds/linux/blob/v3.19/include/uapi/linux/auxvec.h

format ELF executable 3
entry start

;================== code =====================
segment readable executable
;=============================================
 
start:
        mov     eax, 4             ; System call 'write'
        mov     ebx, 1             ; 'stdout'
        mov     ecx, msg1          ; Address of message
        mov     edx, msg1.size
       .end:
        int     0x80

        mov     ebp, esp
        call    show_at

        mov     eax, 1             ; System call 'exit'
        xor     ebx, ebx           ; 
        int     0x80


show_at:
       .argv:
        add     ebp, 4
        mov     ecx, [ebp]
        test    ecx, ecx
        jz      .env
        jmp     .argv
       
       .env:
        add     ebp, 4
        mov     ecx, [ebp]
        test    ecx, ecx
        jz      .at
        jmp     .env
       
       .at:
        add     ebp, 4
        mov     eax, [ebp]          ; AT_ code
        call    print_at

        call    print_eq

        add     ebp, 4
        mov     ebx, [ebp]          ; AT_ value
        push    eax
        mov     eax, ebx
        mov     edi, msghex.val
        mov     ecx, 8
        call    eax2hex
        call    print_hex
        pop     eax        
        call    print_ln
        
        test    eax, eax
        jnz    .at
      .at_end:
        ret

print_hex:
        push    eax ebx ecx edx
        mov     eax, 4              ; System call 'write'
        mov     ebx, 1              ; 'stdout'
        mov     ecx, msghex   ; Address of message
        mov     edx, msghex.size   ; Length  of message
        int     0x80                ; All system calls are done via this interrupt
        pop     edx ecx ebx eax
        ret

print_eq:
        push    eax ebx ecx edx
        mov     eax, 4
        mov     ebx, 1
        mov     ecx, msgeq
        mov     edx, msgeq.size
        int     0x80
        pop     edx ecx ebx eax
        ret

print_ln:
        push    eax ebx ecx edx
        mov     eax, 4
        mov     ebx, 1
        mov     ecx, msgln
        mov     edx, 1
        int     0x80
        pop     edx ecx ebx eax
        ret

print_at:
        push    eax ebx

        mov     esi, at_tbl
       .atloop:
        mov     ecx, [esi]
        add     esi, 4
        mov     edx, [esi]
        add     esi, 4
        cmp     ecx, eax
        jz     .atfnd
        cmp     ecx, 0
        jz     .atno
        jmp    .atloop

       .atfnd:
        mov     ecx, edx
        call    strlen
        mov     eax, 4
        mov     ebx, 1
        int     0x80
        jmp     .atend
        
       .atno:
        mov     edi, msghex.val
        mov     ecx, 8
        call    eax2hex

        mov     eax, 4              ; System call 'write'
        mov     ebx, 1              ; 'stdout'
        mov     ecx, msgnoval   ; Address of message
        mov     edx, msghex.size+2+5   ; Length  of message
        int     0x80                ; All system calls are done via this interrupt
       
       
       .atend:
        pop     ebx eax
        ret


        
        
; Takes eax and turns it into a hex-string in [edi] (16 or 32-bit) 
eax2hex: ;di to di+cx 

        push    eax ebx edx 
        mov     ebx,16 
      .l: 
        xor     edx,edx 
        div     ebx 
        add     edx,"0" 
        cmp     edx,"9" 
        jbe     @f 
        add     edx,"A"-"9"-1 
      @@: 
        mov     [edi+ecx-1],dl 
        sub     ecx,1
        jne     .l
        pop     edx ebx eax 
        ret 

strlen:
; return string [ecx] length in edx
        push    eax
        xor     edx, edx
        mov     edi, ecx
       .l:
        mov     al, [edi + edx]
        test    al, al
        jz     .end
        inc     edx
        jmp     .l
       .end:
        pop     eax
        ret


;================== data =====================
segment readable writeable
;=============================================
msg1_ db 'Message #1', 0xA
msg1_.size = $-msg1

macro defstr id, str
{
    id db str
    .size = $-id
}

defstr msg1, <'Auxiliary Vectors:', 0xA>

msgnoval db '  '
msghex db '0x'
msghex.val db 0,0,0,0,0,0,0,0
msghex.size = $-msghex
db '     '

msgln db 0xA

defstr msgno, <'Unknown '>
defstr msgeq, <' = '>

macro defvec vector, value
{
    vector db '  '#`vector
    STLEN_#vector equ $-vector
    if ($-vector < 18)
      db 17-($-vector) dup(' ')
    end if
    db 0x0
}

macro devidx vector, value
{
    dd value
    dd vector
}

macro deftab mcr
{
    mcr AT_IGNORE,        1               ; Entry should be ignored
    mcr AT_EXECFD,        2               ; File descriptor of program
    mcr AT_PHDR,          3               ; Program headers for program
    mcr AT_PHENT,         4               ; Size of program header entry
    mcr AT_PHNUM,         5               ; Number of program headers
    mcr AT_PAGESZ,        6               ; System page size
    mcr AT_BASE,          7               ; Base address of interpreter
    mcr AT_FLAGS,         8               ; Flags
    mcr AT_ENTRY,         9               ; Entry point of program
    mcr AT_NOTELF,        10              ; Program is not ELF
    mcr AT_UID,           11              ; Real uid
    mcr AT_EUID,          12              ; Effective uid
    mcr AT_GID,           13              ; Real gid
    mcr AT_EGID,          14              ; Effective gid
    mcr AT_PLATFORM,      15              ; string identifying CPU for optimizations 
    mcr AT_HWCAP,         16              ; arch dependent hints at CPU capabilities
    mcr AT_CLKTCK,        17              ; Frequency of times()
    ; AT_* values 18 through 22 are reserved
    mcr AT_SECURE,        23              ; secure mode boolean 
    mcr AT_BASE_PLATFORM, 24             ; string identifying real platform, may
				 ; differ from AT_PLATFORM.
    mcr AT_RANDOM,        25	             ; address of 16 random bytes 
    mcr AT_HWCAP2,        26              ; extension of AT_HWCAP 

    mcr AT_EXECFN,        31	             ; filename of program 
    mcr AT_SYSINFO,       32
    mcr AT_SYSINFO_EHDR,  33

    mcr AT_NULL,          0               ; End of vector
}

; define string table
deftab defvec
at_tbl:
deftab devidx