path: root/hex.e

~ cat labels.e elf.e hex.e | ./evoke > hex && chmod 755 hex && ./hex

~ (buffer start, output point, label offset
~  -- buffer start, output point)
: jmp-rel-imm8-from-here
  over 3 pick - 2 + - jmp-rel-imm8 ;

~ (buffer start, output point, label offset, condition code
~  -- buffer start, output point)
: jmp-cc-rel-imm8-from-here
  swap 2 pick 4 pick - 2 + - swap jmp-cc-rel-imm8 ;

~ (buffer start, output point, label offset -- buffer start, output point)
: call-rel-imm32-from-here
  over 3 pick - 5 + - call-rel-imm32 ;


~ (buffer start, output point -- buffer start, output point)
: output-start-routine
  ~ : blank-line
  ~ : This is the start routine, the first thing that runs when the ELF loads.
  ~ : indent
  current-offset L!' cold-start
  ~ :   The basic registers preserved across syscalls are rbx, rsp, rbp.
  ~ : To avoid redundant moves, we store the buffer pointer in rbx just once,
  ~ : and keep it there. We've made sure our load origin fits in 32 bits, so
  ~ : we can use imm32 for that. We're going to want to do an indirect load
  ~ : from it, so we can't use rbp for this.
  L@' buffer L@' origin + :rbx mov-reg64-imm32
  ~ : blank-line

  current-offset L!' input-loop-start
  L@' read-byte call-rel-imm32-from-here
  ~ : blank-line

  ~ :   If the length is 0, we got EOF. If it's less than zero, we got a read
  ~ : error. Either way, we exit. This is a signed comparison, as it needs to
  ~ : be.
  0 :rax cmp-reg64-imm8
  L@' exit :cc-equal jmp-cc-rel-imm8-from-here
  L@' read-error :cc-less jmp-cc-rel-imm8-from-here
  ~ : blank-line

  ~ : Now that the length is handled, retrieve the input byte.
  :rbx :rax mov-reg64-indirect-reg64
  ~ : blank-line

  ~ : If it's space or linefeed, skip it (go back to the loop start).
  0x20 :rax cmp-reg64-imm8                  ~ : ASCII space
  L@' input-loop-start :cc-equal jmp-cc-rel-imm8-from-here
  0x0a :rax cmp-reg64-imm8                  ~ : ASCII linefeed
  L@' input-loop-start :cc-equal jmp-cc-rel-imm8-from-here
  ~ : If it's a comment, skip the whole thing.
  0x7e :rax cmp-reg64-imm8                  ~ : ASCII tilde
  L@' skip-comment :cc-equal jmp-cc-rel-imm8-from-here
  ~ : blank-line

  ~ : Decode the value, or exit with an error.
  L@' decode-nibble call-rel-imm32-from-here
  ~ : blank-line

  ~ : We use rbp as a place to stash the high nibble.
  :rax :rbp mov-reg64-reg64
  4 :rbp rol-reg64-imm8
  ~ : blank-line

  ~ : Now we read another byte.
  L@' read-byte call-rel-imm32-from-here
  ~ : blank-line

  ~ : Handle the length. A second hex digit is required here.
  0 :rax cmp-reg64-imm8
  L@' unexpected-eof :cc-equal jmp-cc-rel-imm8-from-here
  L@' read-error :cc-less jmp-cc-rel-imm8-from-here
  ~ : blank-line

  ~ : Now that the length is handled, retrieve the input byte.
  :rbx :rax mov-reg64-indirect-reg64
  ~ : blank-line

  ~ : Decode the value, or exit with an error.
  L@' decode-nibble call-rel-imm32-from-here
  ~ : blank-line

  ~ : We OR in the low nibble.
  :rax :rbp or-reg64-reg64
  ~ : blank-line

  ~ : Output the byte. We reuse the buffer as a place to store it.
  :rbp :rbx mov-indirect-reg64-reg64
  :rbx :rsi mov-reg64-reg64                 ~ : buffer pointer
  1 :rdx mov-reg64-imm32                    ~ : buffer length
  1 :rax mov-reg64-imm32                    ~ : syscall number for sys-write
  1 :rdi mov-reg64-imm32                    ~ : file descriptor 1 is stdout
  syscall
  ~ : blank-line

  ~ : Back to the start of the loop.
  L@' input-loop-start jmp-rel-imm8-from-here
  ~ : blank-line

  current-offset L!' skip-comment

  ~ : Read a byte for the comment.
  L@' read-byte call-rel-imm32-from-here
  ~ : blank-line

  ~ : Handle the length. We're allowed to end in a comment.
  0 :rax cmp-reg64-imm8
  L@' exit :cc-equal jmp-cc-rel-imm8-from-here
  L@' read-error :cc-less jmp-cc-rel-imm8-from-here
  ~ : blank-line

  ~ : Now that the length is handled, retrieve the input byte.
  :rbx :rax mov-reg64-indirect-reg64
  ~ : blank-line

  ~ : If it's linefeed, the comment is over.
  0x0a :rax cmp-reg64-imm8                  ~ : ASCII linefeed
  L@' input-loop-start :cc-equal jmp-cc-rel-imm8-from-here
  ~ : blank-line

  ~ : We're still in the comment, keep handling it.
  L@' skip-comment jmp-rel-imm8-from-here
  ~ : deindent
  ;


~   This routine has no expectations; it reads a byte into L' buffer, keeps
~ the return value of the syscall in :rax, and returns to its caller. The
~ caller is responsible for doing something with the return value.
~
~ (output memory start, current output point
~  -- output memory start, current output point)
: output-read-byte
  ~ : blank-line
  ~ : This is the routine named "read-byte".
  ~ : indent
  current-offset L!' read-byte
  ~ : We use self-xor as a concise way to set registers to zero.
  :rax :rax xor-reg64-reg64                 ~ : syscall number for sys-read
  :rdi :rdi xor-reg64-reg64                 ~ : file descriptor 0 is stdin
  :rbx :rsi mov-reg64-reg64                 ~ : buffer pointer
  ~ : We read one byte at a time, because it makes the loop structure simple.
  1 :rdx mov-reg64-imm32                    ~ : buffer length
  syscall
  ret
  ~ : deindent
  ;


~   This routine expects :rax to hold an ASCII byte, which must be a valid
~ hexadecimal digit. When it returns, :rax holds a decoded nibble. If the
~ input is invalid, it jumps to L' invalid-byte instead, thereby ending
~ execution.
~
~ (output memory start, current output point
~  -- output memory start, current output point)
: output-decode-nibble
  ~ : blank-line
  ~ : This is the routine named "decode-nibble".
  ~ : indent
  current-offset L!' decode-nibble

  0x30 :rax sub-reg64-imm8                  ~ : ASCII zero
  ~ If it's negative, jump to the error path.
  L@' invalid-byte :cc-less jmp-cc-rel-imm8-from-here
  10 :rax cmp-reg64-imm8
  ~ This is an unsigned comparison.
  L@' got-nibble :cc-below jmp-cc-rel-imm8-from-here
  0x41 0x30 - :rax sub-reg64-imm8           ~ : ASCII capital A
  ~ If it's negative, jump to the error path.
  L@' invalid-byte :cc-less jmp-cc-rel-imm8-from-here
  ~ To simplify the range adjustment, we do it unconditionally, before
  ~ checking the upper bound.
  10 :rax add-reg64-imm8
  16 :rax cmp-reg64-imm8
  ~ This is an unsigned comparison.
  L@' got-nibble :cc-below jmp-cc-rel-imm8-from-here
  0x61 0x41 - 10 + :rax sub-reg64-imm8      ~ : ASCII lowercase a
  ~ If it's negative, jump to the error path.
  L@' invalid-byte :cc-less jmp-cc-rel-imm8-from-here
  ~ Again, we adjust the range unconditionally, then check the upper bound.
  10 :rax add-reg64-imm8
  16 :rax cmp-reg64-imm8
  ~ This is an unsigned comparison.
  L@' got-nibble :cc-below jmp-cc-rel-imm8-from-here
  ~ It's not hex, so jump to the error path.
  L@' invalid-byte jmp-rel-imm8-from-here

  current-offset L!' got-nibble
  ret
  ~ : deindent
  ;


~ (output memory start, current output point
~  -- output memory start, current output point)
: output-exit
  ~ : blank-line
  ~ : This is the routine named "exit".
  ~ : indent
  current-offset L!' exit
  60 :rax mov-reg64-imm32                   ~ : syscall number for sys-exit
  0 :rdi mov-reg64-imm32                    ~ : exit code
  syscall
  ~ : deindent
  ;


~   Printing an error message makes sure we don't produce a valid-looking
~ binary that inadvertently gets used. So, it's worth it, despite coming at
~ a cost to code size.
~
~ (output memory start, current output point
~  -- output memory start, current output point)
: output-error-handlers
  ~ : blank-line
  ~ : These are the error handler routines.
  ~ : indent
  current-offset L!' invalid-byte
  L@' origin L@' invalid-byte-message + :rsi mov-reg64-imm64
  L' invalid-byte-message-size set-label-non-offset
  L@' invalid-byte-message-size :rdx mov-reg64-imm64
  L@' exit-with-error jmp-rel-imm8-from-here

  current-offset L!' unexpected-eof
  L@' origin L@' unexpected-eof-message + :rsi mov-reg64-imm64
  L' unexpected-eof-message-size set-label-non-offset
  L@' unexpected-eof-message-size :rdx mov-reg64-imm64
  L@' exit-with-error jmp-rel-imm8-from-here

  current-offset L!' read-error
  L@' origin L@' read-error-message + :rsi mov-reg64-imm64
  L' read-error-message-size set-label-non-offset
  L@' read-error-message-size :rdx mov-reg64-imm64
  ~ Fall through.

  current-offset L!' exit-with-error
  1 :rax mov-reg64-imm32                    ~ : syscall number for sys-write
  2 :rdi mov-reg64-imm32                    ~ : file descriptor 2 is stderr
  syscall

  60 :rax mov-reg64-imm32                   ~ : syscall number for sys-exit
  1 :rdi mov-reg64-imm32                    ~ : exit code
  syscall
  ~ : deindent
  ;


~ (output memory start, current output point
~  -- output memory start, current output point)
: output-messages
  ~ : blank-line
  ~ : These are the message strings.
  ~ : indent
  current-offset dup L!' invalid-byte-message 3unroll
  s" Invalid byte." packstring
  current-offset 4 roll - L!' invalid-byte-message-size

  current-offset dup L!' read-error-message 3unroll
  s" Read error." packstring
  current-offset 4 roll - L!' read-error-message-size

  current-offset dup L!' unexpected-eof-message 3unroll
  s" Unexpected EOF." packstring
  current-offset 4 roll - L!' unexpected-eof-message-size

  ~ : deindent
  ;

~ (output memory start, current output point
~  -- output memory start, current output point)
~
~ Everything directly called by all-contents has this same interface.
~
: all-contents
  ~ :   This particular program is 'hex' itself. You of course already need to
  ~ : have a binary copy of it to use this file, but you may find it helpful
  ~ : to have this hex dump anyway, to aid in auditing your binary.
  ~ : blank-line
  0x08000000 L!' origin
  elf-file-header
  elf-program-header-writable
  ~ : blank-line
  output-start-routine
  output-exit
  output-read-byte
  output-decode-nibble
  ~ : blank-line
  output-error-handlers
  output-messages

  ~ : blank-line
  ~ :   This is a buffer that's zero in the ELF, but is written to at runtime
  ~ : and used as a variable.
  ~ : indent
  current-offset L!' buffer 0 pack64
  ~ : deindent

  current-offset L!' total-size
  ~ : blank-line
  ~ : This is the end of the hex dump.
  ;

' all-contents entry-to-execution-token label-loop
swap sys-write bye