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< title > Mu - 050_write.subx< / title >
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< a href = 'https://github.com/akkartik/mu/blob/master/050_write.subx' > https://github.com/akkartik/mu/blob/master/050_write.subx< / a >
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< pre id = 'vimCodeElement' >
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< span id = "L1" class = "LineNr" > 1 < / span > < span class = "subxComment" > # _write: write to a file descriptor (fd)< / span >
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< span id = "L2" class = "LineNr" > 2 < / span >
< span id = "L3" class = "LineNr" > 3 < / span > == code
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< span id = "L4" class = "LineNr" > 4 < / span > < span class = "subxComment" > # instruction effective address register displacement immediate< / span >
< span id = "L5" class = "LineNr" > 5 < / span > < span class = "subxS1Comment" > # . op subop mod rm32 base index scale r32< / span >
< span id = "L6" class = "LineNr" > 6 < / span > < span class = "subxS1Comment" > # . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes< / span >
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< span id = "L7" class = "LineNr" > 7 < / span >
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< span id = "L8" class = "LineNr" > 8 < / span > < span class = "SpecialChar" > Entry< / span > : < span class = "subxComment" > # just exit; can't test _write just yet< / span >
< span id = "L9" class = "LineNr" > 9 < / span > < span class = "subxS1Comment" > # . syscall(exit, 0)< / span >
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< span id = "L10" class = "LineNr" > 10 < / span > bb/copy-to-ebx 0/imm32
< span id = "L11" class = "LineNr" > 11 < / span > b8/copy-to-eax 1/imm32/exit
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< span id = "L12" class = "LineNr" > 12 < / span > cd/syscall 0x80/imm8
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< span id = "L13" class = "LineNr" > 13 < / span >
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< span id = "L14" class = "LineNr" > 14 < / span > < span class = "subxComment" > # Since this is the first file of SubX code, a note about type comments.< / span >
< span id = "L15" class = "LineNr" > 15 < / span > < span class = "subxComment" > # Eventually we'll build a slightly higher-level safe language atop SubX.< / span >
< span id = "L16" class = "LineNr" > 16 < / span > < span class = "subxComment" > # Even though we don't have the safe language yet, we'll start thinking in< / span >
< span id = "L17" class = "LineNr" > 17 < / span > < span class = "subxComment" > # terms of the higher-level types in comments.< / span >
< span id = "L18" class = "LineNr" > 18 < / span > < span class = "subxComment" > #< / span >
< span id = "L19" class = "LineNr" > 19 < / span > < span class = "subxComment" > # Mu will have two kinds of addresses:< / span >
< span id = "L20" class = "LineNr" > 20 < / span > < span class = "subxComment" > # - 'ref' which is used to point to a unique element, because machine< / span >
< span id = "L21" class = "LineNr" > 21 < / span > < span class = "subxComment" > # code can't store large types in registers.< / span >
< span id = "L22" class = "LineNr" > 22 < / span > < span class = "subxComment" > # - 'handle' which can point to a heap allocation, different heap allocations< / span >
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< span id = "L23" class = "LineNr" > 23 < / span > < span class = "subxComment" > # at different times, or even at times nothing at all. (Later on handles< / span >
< span id = "L24" class = "LineNr" > 24 < / span > < span class = "subxComment" > # will turn into fat pointers to enable safe reclamation. But in unsafe< / span >
< span id = "L25" class = "LineNr" > 25 < / span > < span class = "subxComment" > # levels we'll just never reclaim them, and handles will be word-sized just< / span >
< span id = "L26" class = "LineNr" > 26 < / span > < span class = "subxComment" > # like refs.)< / span >
< span id = "L27" class = "LineNr" > 27 < / span > < span class = "subxComment" > #< / span >
< span id = "L28" class = "LineNr" > 28 < / span > < span class = "subxComment" > # The type 'address' can be obtained from either a ref or handle, but it can< / span >
< span id = "L29" class = "LineNr" > 29 < / span > < span class = "subxComment" > # only be stored on the stack (say to pass objects by reference).< / span >
< span id = "L30" class = "LineNr" > 30 < / span > < span class = "subxComment" > # Conversely, a ref can't be copied into another ref, only to an address (which< / span >
< span id = "L31" class = "LineNr" > 31 < / span > < span class = "subxComment" > # by construction has a shorter lifetime).< / span >
< span id = "L32" class = "LineNr" > 32 < / span > < span class = "subxComment" > #< / span >
< span id = "L33" class = "LineNr" > 33 < / span > < span class = "subxComment" > # Beginnings of a lattice of types:< / span >
< span id = "L34" class = "LineNr" > 34 < / span > < span class = "subxComment" > # You can convert a ref or handle to an address, but not the other way around.< / span >
< span id = "L35" class = "LineNr" > 35 < / span > < span class = "subxComment" > # You can convert addresses to ints, but not the other way around.< / span >
< span id = "L36" class = "LineNr" > 36 < / span >
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< span id = "L37" class = "LineNr" > 37 < / span > < span class = "subxMinorFunction" > _write< / span > : < span class = "subxComment" > # fd : int, s : (addr array byte)< / span >
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< span id = "L38" class = "LineNr" > 38 < / span > < span class = "subxS1Comment" > # . prologue< / span >
< span id = "L39" class = "LineNr" > 39 < / span > 55/push-ebp
< span id = "L40" class = "LineNr" > 40 < / span > 89/copy 3/mod/direct 5/rm32/ebp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 4/r32/esp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "subxComment" > # copy esp to ebp< / span >
< span id = "L41" class = "LineNr" > 41 < / span > < span class = "subxS1Comment" > # . save registers< / span >
< span id = "L42" class = "LineNr" > 42 < / span > 50/push-eax
< span id = "L43" class = "LineNr" > 43 < / span > 51/push-ecx
< span id = "L44" class = "LineNr" > 44 < / span > 52/push-edx
< span id = "L45" class = "LineNr" > 45 < / span > 53/push-ebx
< span id = "L46" class = "LineNr" > 46 < / span > < span class = "subxComment" > # syscall(write, fd, (data) s+4, (size) *s)< / span >
< span id = "L47" class = "LineNr" > 47 < / span > < span class = "subxS1Comment" > # . fd : ebx< / span >
< span id = "L48" class = "LineNr" > 48 < / span > 8b/copy 1/mod/*+disp8 5/rm32/ebp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 3/r32/ebx 8/disp8 < span class = "Normal" > . < / span > < span class = "subxComment" > # copy *(ebp+8) to ebx< / span >
< span id = "L49" class = "LineNr" > 49 < / span > < span class = "subxS1Comment" > # . data : ecx = s+4< / span >
< span id = "L50" class = "LineNr" > 50 < / span > 8b/copy 1/mod/*+disp8 5/rm32/ebp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 1/r32/ecx 0xc/disp8 < span class = "Normal" > . < / span > < span class = "subxComment" > # copy *(ebp+12) to ecx< / span >
< span id = "L51" class = "LineNr" > 51 < / span > 81 0/subop/add 3/mod/direct 1/rm32/ecx < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 4/imm32 < span class = "subxComment" > # add to ecx< / span >
< span id = "L52" class = "LineNr" > 52 < / span > < span class = "subxS1Comment" > # . size : edx = *s< / span >
< span id = "L53" class = "LineNr" > 53 < / span > 8b/copy 1/mod/*+disp8 5/rm32/ebp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 2/r32/edx 0xc/disp8 < span class = "Normal" > . < / span > < span class = "subxComment" > # copy *(ebp+12) to edx< / span >
< span id = "L54" class = "LineNr" > 54 < / span > 8b/copy 0/mod/indirect 2/rm32/edx < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 2/r32/edx < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "subxComment" > # copy *edx to edx< / span >
< span id = "L55" class = "LineNr" > 55 < / span > < span class = "subxS1Comment" > # . syscall< / span >
< span id = "L56" class = "LineNr" > 56 < / span > b8/copy-to-eax 4/imm32/write
< span id = "L57" class = "LineNr" > 57 < / span > cd/syscall 0x80/imm8
< span id = "L58" class = "LineNr" > 58 < / span > < span class = "subxComment" > # if (eax < 0) abort< / span >
< span id = "L59" class = "LineNr" > 59 < / span > 3d/compare-eax-with 0/imm32
< span id = "L60" class = "LineNr" > 60 < / span > 0f 8c/jump-if-lesser $_write:abort/disp32
< span id = "L61" class = "LineNr" > 61 < / span > < span class = "Constant" > $_write:end< / span > :
< span id = "L62" class = "LineNr" > 62 < / span > < span class = "subxS1Comment" > # . restore registers< / span >
< span id = "L63" class = "LineNr" > 63 < / span > 5b/pop-to-ebx
< span id = "L64" class = "LineNr" > 64 < / span > 5a/pop-to-edx
< span id = "L65" class = "LineNr" > 65 < / span > 59/pop-to-ecx
< span id = "L66" class = "LineNr" > 66 < / span > 58/pop-to-eax
< span id = "L67" class = "LineNr" > 67 < / span > < span class = "subxS1Comment" > # . epilogue< / span >
< span id = "L68" class = "LineNr" > 68 < / span > 89/copy 3/mod/direct 4/rm32/esp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > 5/r32/ebp < span class = "Normal" > . < / span > < span class = "Normal" > . < / span > < span class = "subxComment" > # copy ebp to esp< / span >
< span id = "L69" class = "LineNr" > 69 < / span > 5d/pop-to-ebp
< span id = "L70" class = "LineNr" > 70 < / span > c3/return
< span id = "L71" class = "LineNr" > 71 < / span >
< span id = "L72" class = "LineNr" > 72 < / span > < span class = "Constant" > $_write:abort< / span > :
< span id = "L73" class = "LineNr" > 73 < / span > < span class = "subxComment" > # can't write a message here for risk of an infinite loop, so we'll use a special exit code instead< / span >
< span id = "L74" class = "LineNr" > 74 < / span > < span class = "subxS1Comment" > # . syscall(exit, 255)< / span >
< span id = "L75" class = "LineNr" > 75 < / span > bb/copy-to-ebx 0xff/imm32
< span id = "L76" class = "LineNr" > 76 < / span > b8/copy-to-eax 1/imm32/exit
< span id = "L77" class = "LineNr" > 77 < / span > cd/syscall 0x80/imm8
< span id = "L78" class = "LineNr" > 78 < / span > < span class = "subxComment" > # never gets here< / span >
< span id = "L79" class = "LineNr" > 79 < / span >
< span id = "L80" class = "LineNr" > 80 < / span > < span class = "subxS2Comment" > # . . vim: nowrap:textwidth=0< / span >
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