att asm stdin
.text
.global _start
_start:
# read(STDIN_FILENO, buf, 1)
movl $1, %edx # size_t nbyte
movl $buf, %ecx # void *buf
movl $0, %ebx # int filedes
movl $3, %eax # sys_read
int $0x80
cmp $1, %eax
jne bye # EOF or read() error
cmp $'A', (%ecx)
jl output # *buf < 'A'
cmp $'Z', (%ecx)
jg output # *buf > 'Z'
je z # *buf == 'Z'
incl (%ecx) # *buf >= 'A' && *buf < 'Z'
jmp output
z:
movl $'A', (%ecx)
output:
# write(STDOUT_FILENO, buf, 1)
movl $1, %ebx # int filedes
movl $4, %eax # sys_write
int $0x80
jmp _start
bye:
# exit(0)
movl $0, %ebx # int status
movl $1, %eax # sys_exit
int $0x80
.data
buf:
.byte 0