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I was 'returning' a phantom value from 'write' when the underlying '_write'
returns nothing.

In general, returning counts of bytes written is not so useful for error
checking when my primitives abstract away from that. We'll come back to
error signalling later.
This commit is contained in:
Kartik Agaram 2018-12-03 16:38:44 -08:00
parent 5082923e81
commit 5e27c7f13e
5 changed files with 53 additions and 53 deletions
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98
html/subx/056write.subx.html
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@ -92,55 +92,55 @@ if ('onhashchange' in window) {
<span id="L27" class="LineNr"> 27 </span> b8/copy-to-EAX 1/imm32
<span id="L28" class="LineNr"> 28 </span> cd/syscall 0x80/imm8
<span id="L29" class="LineNr"> 29 </span>
<span id="L30" class="LineNr"> 30 </span><span class="subxFunction">write</span>: <span class="subxComment"># f : fd or (address stream), s : (address array byte) -&gt; bytes_written/EAX</span>
<span id="L31" class="LineNr"> 31 </span> <span class="subxComment"># (If we ever leave the Linux kernel behind, it may be better to return</span>
<span id="L32" class="LineNr"> 32 </span> <span class="subxComment"># the number of bytes *not* written. Success would then be signaled by</span>
<span id="L33" class="LineNr"> 33 </span> <span class="subxComment"># returning 0.)</span>
<span id="L34" class="LineNr"> 34 </span> <span class="subxS1Comment"># . prolog</span>
<span id="L35" class="LineNr"> 35 </span> 55/push-EBP
<span id="L36" class="LineNr"> 36 </span> 89/copy 3/mod/direct 5/rm32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/r32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy ESP to EBP</span>
<span id="L37" class="LineNr"> 37 </span> <span class="subxComment"># if (f &lt; 0x08000000) _write(f, s), return # f can't be a user-mode address, so treat it as a kernel file descriptor</span>
<span id="L38" class="LineNr"> 38 </span> 81 7/subop/compare 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/disp8 0x08000000/imm32 <span class="subxComment"># compare *(EBP+8)</span>
<span id="L39" class="LineNr"> 39 </span> 7d/jump-if-greater-or-equal $write:fake/disp8
<span id="L40" class="LineNr"> 40 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L41" class="LineNr"> 41 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+12)</span>
<span id="L42" class="LineNr"> 42 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+8)</span>
<span id="L43" class="LineNr"> 43 </span> <span class="subxS2Comment"># . . call</span>
<span id="L44" class="LineNr"> 44 </span> e8/call _write/disp32
<span id="L45" class="LineNr"> 45 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L46" class="LineNr"> 46 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/imm32 <span class="subxComment"># add to ESP</span>
<span id="L47" class="LineNr"> 47 </span> eb/jump $write:end/disp8
<span id="L48" class="LineNr"> 48 </span><span class="Constant">$write:fake</span>:
<span id="L49" class="LineNr"> 49 </span> <span class="subxComment"># otherwise, treat 'f' as a stream to append to</span>
<span id="L50" class="LineNr"> 50 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L51" class="LineNr"> 51 </span> 51/push-ECX
<span id="L52" class="LineNr"> 52 </span> 52/push-EDX
<span id="L53" class="LineNr"> 53 </span> 53/push-EBX
<span id="L54" class="LineNr"> 54 </span> <span class="subxComment"># ECX = f</span>
<span id="L55" class="LineNr"> 55 </span> 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 1/r32/ECX 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(EBP+8) to ECX</span>
<span id="L56" class="LineNr"> 56 </span> <span class="subxComment"># EDX = f-&gt;write</span>
<span id="L57" class="LineNr"> 57 </span> 8b/copy 0/mod/indirect 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 2/r32/EDX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy *ECX to EDX</span>
<span id="L58" class="LineNr"> 58 </span> <span class="subxComment"># EBX = f-&gt;length</span>
<span id="L59" class="LineNr"> 59 </span> 8b/copy 1/mod/*+disp8 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 3/r32/EBX 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(ECX+8) to EBX</span>
<span id="L60" class="LineNr"> 60 </span> <span class="subxComment"># EAX = _append-3(&amp;f-&gt;data[f-&gt;write], &amp;f-&gt;data[f-&gt;length], s)</span>
<span id="L61" class="LineNr"> 61 </span> <span class="subxS2Comment"># . . push s</span>
<span id="L62" class="LineNr"> 62 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+12)</span>
<span id="L63" class="LineNr"> 63 </span> <span class="subxS2Comment"># . . push &amp;f-&gt;data[f-&gt;length]</span>
<span id="L64" class="LineNr"> 64 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 3/index/EBX <span class="CommentedCode"> . </span> 3/r32/EBX 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy ECX+EBX+12 to EBX</span>
<span id="L65" class="LineNr"> 65 </span> 53/push-EBX
<span id="L66" class="LineNr"> 66 </span> <span class="subxS2Comment"># . . push &amp;f-&gt;data[f-&gt;write]</span>
<span id="L67" class="LineNr"> 67 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 2/index/EDX <span class="CommentedCode"> . </span> 3/r32/EBX 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy ECX+EDX+12 to EBX</span>
<span id="L68" class="LineNr"> 68 </span> 53/push-EBX
<span id="L69" class="LineNr"> 69 </span> <span class="subxS2Comment"># . . call</span>
<span id="L70" class="LineNr"> 70 </span> e8/call _append-3/disp32
<span id="L71" class="LineNr"> 71 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L72" class="LineNr"> 72 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/imm32 <span class="subxComment"># add to ESP</span>
<span id="L73" class="LineNr"> 73 </span> <span class="subxComment"># f-&gt;write += EAX</span>
<span id="L74" class="LineNr"> 74 </span> 01/add 0/mod/indirect 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/r32/EAX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># add EAX to *ECX</span>
<span id="L75" class="LineNr"> 75 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L76" class="LineNr"> 76 </span> 5b/pop-to-EBX
<span id="L77" class="LineNr"> 77 </span> 5a/pop-to-EDX
<span id="L78" class="LineNr"> 78 </span> 59/pop-to-ECX
<span id="L30" class="LineNr"> 30 </span><span class="subxComment"># TODO: come up with a way to signal when a write to disk fails</span>
<span id="L31" class="LineNr"> 31 </span><span class="subxFunction">write</span>: <span class="subxComment"># f : fd or (address stream), s : (address array byte) -&gt; &lt;void&gt;</span>
<span id="L32" class="LineNr"> 32 </span> <span class="subxS1Comment"># . prolog</span>
<span id="L33" class="LineNr"> 33 </span> 55/push-EBP
<span id="L34" class="LineNr"> 34 </span> 89/copy 3/mod/direct 5/rm32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 4/r32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy ESP to EBP</span>
<span id="L35" class="LineNr"> 35 </span> <span class="subxComment"># if (f &lt; 0x08000000) _write(f, s), return # f can't be a user-mode address, so treat it as a kernel file descriptor</span>
<span id="L36" class="LineNr"> 36 </span> 81 7/subop/compare 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/disp8 0x08000000/imm32 <span class="subxComment"># compare *(EBP+8)</span>
<span id="L37" class="LineNr"> 37 </span> 7d/jump-if-greater-or-equal $write:fake/disp8
<span id="L38" class="LineNr"> 38 </span> <span class="subxS2Comment"># . . push args</span>
<span id="L39" class="LineNr"> 39 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+12)</span>
<span id="L40" class="LineNr"> 40 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+8)</span>
<span id="L41" class="LineNr"> 41 </span> <span class="subxS2Comment"># . . call</span>
<span id="L42" class="LineNr"> 42 </span> e8/call _write/disp32
<span id="L43" class="LineNr"> 43 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L44" class="LineNr"> 44 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 8/imm32 <span class="subxComment"># add to ESP</span>
<span id="L45" class="LineNr"> 45 </span> eb/jump $write:end/disp8
<span id="L46" class="LineNr"> 46 </span><span class="Constant">$write:fake</span>:
<span id="L47" class="LineNr"> 47 </span> <span class="subxComment"># otherwise, treat 'f' as a stream to append to</span>
<span id="L48" class="LineNr"> 48 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L49" class="LineNr"> 49 </span> 50/push-EAX
<span id="L50" class="LineNr"> 50 </span> 51/push-ECX
<span id="L51" class="LineNr"> 51 </span> 52/push-EDX
<span id="L52" class="LineNr"> 52 </span> 53/push-EBX
<span id="L53" class="LineNr"> 53 </span> <span class="subxComment"># ECX = f</span>
<span id="L54" class="LineNr"> 54 </span> 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 1/r32/ECX 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(EBP+8) to ECX</span>
<span id="L55" class="LineNr"> 55 </span> <span class="subxComment"># EDX = f-&gt;write</span>
<span id="L56" class="LineNr"> 56 </span> 8b/copy 0/mod/indirect 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 2/r32/EDX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy *ECX to EDX</span>
<span id="L57" class="LineNr"> 57 </span> <span class="subxComment"># EBX = f-&gt;length</span>
<span id="L58" class="LineNr"> 58 </span> 8b/copy 1/mod/*+disp8 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 3/r32/EBX 8/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy *(ECX+8) to EBX</span>
<span id="L59" class="LineNr"> 59 </span> <span class="subxComment"># EAX = _append-3(&amp;f-&gt;data[f-&gt;write], &amp;f-&gt;data[f-&gt;length], s)</span>
<span id="L60" class="LineNr"> 60 </span> <span class="subxS2Comment"># . . push s</span>
<span id="L61" class="LineNr"> 61 </span> ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># push *(EBP+12)</span>
<span id="L62" class="LineNr"> 62 </span> <span class="subxS2Comment"># . . push &amp;f-&gt;data[f-&gt;length]</span>
<span id="L63" class="LineNr"> 63 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 3/index/EBX <span class="CommentedCode"> . </span> 3/r32/EBX 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy ECX+EBX+12 to EBX</span>
<span id="L64" class="LineNr"> 64 </span> 53/push-EBX
<span id="L65" class="LineNr"> 65 </span> <span class="subxS2Comment"># . . push &amp;f-&gt;data[f-&gt;write]</span>
<span id="L66" class="LineNr"> 66 </span> 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 2/index/EDX <span class="CommentedCode"> . </span> 3/r32/EBX 0xc/disp8 <span class="CommentedCode"> . </span> <span class="subxComment"># copy ECX+EDX+12 to EBX</span>
<span id="L67" class="LineNr"> 67 </span> 53/push-EBX
<span id="L68" class="LineNr"> 68 </span> <span class="subxS2Comment"># . . call</span>
<span id="L69" class="LineNr"> 69 </span> e8/call _append-3/disp32
<span id="L70" class="LineNr"> 70 </span> <span class="subxS2Comment"># . . discard args</span>
<span id="L71" class="LineNr"> 71 </span> 81 0/subop/add 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0xc/imm32 <span class="subxComment"># add to ESP</span>
<span id="L72" class="LineNr"> 72 </span> <span class="subxComment"># f-&gt;write += EAX</span>
<span id="L73" class="LineNr"> 73 </span> 01/add 0/mod/indirect 1/rm32/ECX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 0/r32/EAX <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># add EAX to *ECX</span>
<span id="L74" class="LineNr"> 74 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L75" class="LineNr"> 75 </span> 5b/pop-to-EBX
<span id="L76" class="LineNr"> 76 </span> 5a/pop-to-EDX
<span id="L77" class="LineNr"> 77 </span> 59/pop-to-ECX
<span id="L78" class="LineNr"> 78 </span> 58/pop-to-EAX
<span id="L79" class="LineNr"> 79 </span><span class="Constant">$write:end</span>:
<span id="L80" class="LineNr"> 80 </span> <span class="subxS1Comment"># . epilog</span>
<span id="L81" class="LineNr"> 81 </span> 89/copy 3/mod/direct 4/rm32/ESP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> 5/r32/EBP <span class="CommentedCode"> . </span> <span class="CommentedCode"> . </span> <span class="subxComment"># copy EBP to ESP</span>

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@ -27,10 +27,8 @@
b8/copy-to-EAX 1/imm32
cd/syscall 0x80/imm8
write: # f : fd or (address stream), s : (address array byte) -> bytes_written/EAX
# (If we ever leave the Linux kernel behind, it may be better to return
# the number of bytes *not* written. Success would then be signaled by
# returning 0.)
# TODO: come up with a way to signal when a write to disk fails
write: # f : fd or (address stream), s : (address array byte) -> <void>
# . prolog
55/push-EBP
89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
@ -48,6 +46,7 @@ write: # f : fd or (address stream), s : (address array byte) -> bytes_written/
$write:fake:
# otherwise, treat 'f' as a stream to append to
# . save registers
50/push-EAX
51/push-ECX
52/push-EDX
53/push-EBX
@ -76,6 +75,7 @@ $write:fake:
5b/pop-to-EBX
5a/pop-to-EDX
59/pop-to-ECX
58/pop-to-EAX
$write:end:
# . epilog
89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP

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