从文件中读取单个字符会返回-9错误值

Question

我开发了以下代码来打开一个名为in.put的输入文件，并从中读取一个字符。但是gdb调试器显示读取单个字符会在-9寄存器返回eax。读取错误的位置显示在代码中。我无法弄清楚我错过了什么，有人知道吗：

section .data   ;initialized data

;input file
input           db      'in.put'
inputhandle:    dd      0x00    ;place-holder for input file handle

section .bss    ;uninitialized data

;prepare memory location for reading a character on file
charbuff:       resb    0x01

section .text   ;instructions
global _start
_start:

    ;open file at read-write permission
    mov ecx, 1          ;read-write
    mov ebx, input      ;file name pointer
    mov eax, 5          ;open
    int 0x80

    ;check if open is good
    cmp eax, 0
    jle end                     ;if eax<=0 , jump end
    mov [inputhandle], eax      ;store returned file handle

    ;read a character on file
    mov edx, 0x01               ;length of signle-character memory location = 0x01
    mov ecx, charbuff           ;pointer to single-character memory location
    mov ebx, [inputhandle]      ;file handle
    mov eax, 3                  ;system read
    int 0x80
    ;
    ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    ;at this point, debugger shows
    ;the returned value in eax is -9
    ;I'm not sure why
    ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    ;

end:
    ;close file
    mov ebx, [inputhandle]              ;file handle
    mov eax, 6                          ;system close
    int 0x80

    ; exit
    mov ebx, 0
    mov eax, 1
    int 0x80