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https://github.com/pkivolowitz/asm_book.git
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89 lines
2.2 KiB
ArmAsm
89 lines
2.2 KiB
ArmAsm
/* Perry Kivolowitz
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Example of file operations.
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*/
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.text
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.global main
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.align 2
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/* This program will
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* open() a file in the current directory,
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* write() some text to it,
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* seek back to the beginning of the file,
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* read() each line, printing it
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* close() the file
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*/
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retval .req w27
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fd .req w28
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main: stp x29, x30, [sp, -16]!
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stp x27, x28, [sp, -16]!
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bl open_file
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// w0 will contain either the file descriptor of the new
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// file or -1 for a failure. Note that the value in w0
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// has also been copied to "fd" - a register alias.
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cmp w0, wzr
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bge 1f
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// If we get here, the open has failed. Use perror() to
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// print a meaningful error and branch to exit. The return
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// code of the program will be set to non-zero inside open_fail.
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bl open_fail
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b 99f
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1: // When we get here, the file is open. Write some data to it.
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// If write_file returns non-zero, it signifies an error. If
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// so, branch to the file closing code since the file is open.
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// The error message will be printed in write_data.
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bl write_data
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cbnz w0, 10f
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// When we get here, we are done. Close the file.
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10: mov w0, fd
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bl close
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mov retval, wzr
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99: ldp x27, x28, [sp], 16
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ldp x29, x30, [sp], 16
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mov w0, retval
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ret
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/* This function attempts to open a file for both reading and
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writing. Return values will be checked to ensure the file is
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opened. If successful, 0 is returned (and the file descriptor
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is squirreled away in register "fd".
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*/
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open_file:
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stp x29, x30, [sp, -16]!
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ldr x0, =fname
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mov w1, 0102
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mov w2, 0600
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bl open
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mov fd, w0
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ldp x29, x30, [sp], 16
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ret
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/* This function uses perror to print a meaningful error
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message in the event of an open failure.
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*/
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open_fail:
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stp x29, x30, [sp, -16]!
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ldr x0, =fname
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bl perror
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mov retval, 1
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ldp x29, x30, [sp], 16
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ret
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write_data:
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stp x29, x30, [sp, -16]!
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ldp x29, x30, [sp], 16
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ret
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.data
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prog: .asciz "file_ops"
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fname: .asciz "test.txt"
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txt: .asciz "some data\n"
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txt_s: .word txt_s - txt - 1 // strlen(txt)
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.end
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