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authorKartik Agaram <vc@akkartik.com>2020-12-23 22:48:47 -0800
committerKartik Agaram <vc@akkartik.com>2020-12-23 22:48:47 -0800
commit169adc36d3d90302a9837b9b1dc1b94de43e2350 (patch)
tree510e8d91ff78dd546c6b292b6092e7e29c5f1eb2 /html/119error-byte.subx.html
parenta94ac8f06826571666ea0a88feb3a4bf35b4ddfe (diff)
downloadmu-169adc36d3d90302a9837b9b1dc1b94de43e2350.tar.gz
7394
I think https://stackoverflow.com/questions/37618111/keyboard-irq-within-an-x86-kernel
has more insight to provide. Among other things the comment about grub
may answer the distinction between entry 0x21 and entry 9.
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# We can't really do much with null-terminated kernel strings, and we don't
# want to. Let's turn them into regular length-prefixed strings at the first
# opportunity.

== code

kernel-string-to-string:  # ad: (addr allocation-descriptor), in: (addr kernel-string), out: (addr handle array byte)
    # . prologue
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    51/push-ecx
    52/push-edx
    53/push-ebx
    56/push-esi
    57/push-edi
    # var len/ecx: int = length(in)
    (kernel-string-length *(ebp+0xc))
    89/<- %ecx 0/r32/eax
    # result = allocate-array(ad, len)
    (allocate-array *(ebp+8) %ecx *(ebp+0x10))
    # var c/edx: byte = 0
    ba/copy-to-edx 0/imm32
    # var src/esi: (addr byte) = in
    8b/-> *(ebp+0xc) 6/r32/esi
    # var dest/edi: (addr byte) = result->data
    8b/-> *(ebp+0x10) 7/r32/edi
    (lookup *edi *(edi+4))  # => eax
    8d/copy-address *(eax+4) 7/r32/edi
    {
$kernel-string-to-string:loop:
      # c = *src
      8a/byte-> *esi 2/r32/dl
      # if (c == 0) break
      81 7/subop/compare %edx 0/imm32
      74/jump-if-= break/disp8
      # *dest = c
      88/byte<- *edi 2/r32/dl
      # ++src
      46/increment-esi
      # ++dest
      47/increment-edi
      eb/jump loop/disp8
    }
$kernel-string-to-string:end:
    # . restore registers
    5f/pop-to-edi
    5e/pop-to-esi
    5b/pop-to-ebx
    5a/pop-to-edx
    59/pop-to-ecx
    # . epilogue
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

kernel-string-length:  # in: (addr kernel-string) -> result/eax: int
    # . prologue
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    51/push-ecx
    52/push-edx
    # result = 0
    b8/copy-to-eax 0/imm32
    # var c/ecx: byte = 0
    b9/copy-to-ecx 0/imm32
    # var curr/edx: (addr byte) = in
    8b/-> *(ebp+8) 2/r32/edx
    {
$kernel-string-length:loop:
      # c = *curr
      8a/byte-> *edx 1/r32/ecx
      # if (c == 0) break
      81 7/subop/compare %ecx 0/imm32
      74/jump-if-= break/disp8
      # ++curr
      42/increment-edx
      # ++result
      40/increment-eax
      #
      eb/jump loop/disp8
    }
$kernel-string-length:end:
    # . restore registers
    5a/pop-to-edx
    59/pop-to-ecx
    # . epilogue
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return