html/linux/101_write.subx.html


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<a href='https://github.com/akkartik/mu/blob/main/linux/101_write.subx'>https://github.com/akkartik/mu/blob/main/linux/101_write.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># _write: write to a file descriptor (fd)</span>
<span id="L2" class="LineNr"> 2 </span>
<span id="L3" class="LineNr"> 3 </span>== code
<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>
<span id="L7" class="LineNr"> 7 </span>
<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>    bb/copy-to-ebx  0/imm32
<span id="L10" class="LineNr">10 </span>    e8/call  <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L11" class="LineNr">11 </span>
<span id="L12" class="LineNr">12 </span><span class="subxMinorFunction">_write</span>:  <span class="subxComment"># fd: int, s: (addr array byte)</span>
<span id="L13" class="LineNr">13 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L14" class="LineNr">14 </span>    55/push-ebp
<span id="L15" class="LineNr">15 </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="L16" class="LineNr">16 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L17" class="LineNr">17 </span>    50/push-eax
<span id="L18" class="LineNr">18 </span>    51/push-ecx
<span id="L19" class="LineNr">19 </span>    52/push-edx
<span id="L20" class="LineNr">20 </span>    53/push-ebx
<span id="L21" class="LineNr">21 </span>    <span class="subxComment"># syscall(write, fd, (data) s+4, (size) *s)</span>
<span id="L22" class="LineNr">22 </span>    <span class="subxS1Comment"># . ebx = fd</span>
<span id="L23" class="LineNr">23 </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="L24" class="LineNr">24 </span>    <span class="subxS1Comment"># . var data/ecx: (addr byte) = s+4</span>
<span id="L25" class="LineNr">25 </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="L26" class="LineNr">26 </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="L27" class="LineNr">27 </span>    <span class="subxS1Comment"># . var size/edx: int = *s</span>
<span id="L28" class="LineNr">28 </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="L29" class="LineNr">29 </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="L30" class="LineNr">30 </span>    <span class="subxS1Comment"># . syscall</span>
<span id="L31" class="LineNr">31 </span>    e8/call  <a href='000init.subx.html#L29'>syscall_write</a>/disp32
<span id="L32" class="LineNr">32 </span>    <span class="subxComment"># if (eax &lt; 0) abort</span>
<span id="L33" class="LineNr">33 </span>    3d/compare-eax-with  0/imm32
<span id="L34" class="LineNr">34 </span>    0f 8c/jump-if-&lt;  $_write:abort/disp32
<span id="L35" class="LineNr">35 </span><span class="Constant">$_write:end</span>:
<span id="L36" class="LineNr">36 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L37" class="LineNr">37 </span>    5b/pop-to-ebx
<span id="L38" class="LineNr">38 </span>    5a/pop-to-edx
<span id="L39" class="LineNr">39 </span>    59/pop-to-ecx
<span id="L40" class="LineNr">40 </span>    58/pop-to-eax
<span id="L41" class="LineNr">41 </span>    <span class="subxS1Comment"># . epilogue</span>
<span id="L42" class="LineNr">42 </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="L43" class="LineNr">43 </span>    5d/pop-to-ebp
<span id="L44" class="LineNr">44 </span>    c3/return
<span id="L45" class="LineNr">45 </span>
<span id="L46" class="LineNr">46 </span><span class="Constant">$_write:abort</span>:
<span id="L47" class="LineNr">47 </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="L48" class="LineNr">48 </span>    <span class="subxS1Comment"># . syscall(exit, 255)</span>
<span id="L49" class="LineNr">49 </span>    bb/copy-to-ebx  0xff/imm32
<span id="L50" class="LineNr">50 </span>    e8/call  <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L51" class="LineNr">51 </span>    <span class="subxComment"># never gets here</span>
<span id="L52" class="LineNr">52 </span>
<span id="L53" class="LineNr">53 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
</pre>
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<!-- vim: set foldmethod=manual : -->
//: A big convenience high-level languages provide is the ability to name memory
//: locations. In Mu, a transform called 'transform_names' provides this
//: convenience.

:(scenario transform_names)
def main [
  x:num <- copy 0
]
+name: assign x 1
+mem: storing 0 in location 1

:(scenarios transform)
:(scenario transform_names_fails_on_use_before_define)
% Hide_errors = true;
def main [
  x:num <- copy y:num
]
+error: main: tried to read ingredient 'y' in 'x:num <- copy y:num' but it hasn't been written to yet
# todo: detect conditional defines

:(after "Transform.push_back(compute_container_sizes)")
Transform.push_back(transform_names);  // idempotent

:(before "End Globals")
map<recipe_ordinal, map<string, int> > Name;

//: the Name map is a global, so save it before tests and reset it for every
//: test, just to be safe.
:(before "End Globals")
map<recipe_ordinal, map<string, int> > Name_snapshot;
:(before "End save_snapshots")
Name_snapshot = Name;
:(before "End restore_snapshots")
Name = Name_snapshot;

:(code)
void transform_names(const recipe_ordinal r) {
  recipe& caller = get(Recipe, r);
  trace(9991, "transform") << "--- transform names for recipe " << caller.name << end();
  bool names_used = false;
  bool numeric_locations_used = false;
  map<string, int>& names = Name[r];
  // store the indices 'used' so far in the map
  int& curr_idx = names[""];
  ++curr_idx;  // avoid using index 0, benign skip in some other cases
  for (int i = 0;  i < SIZE(caller.steps);  ++i) {
    instruction& inst = caller.steps.at(i);
    // End transform_names(inst) Special-cases
    // map names to addresses
    for (int in = 0;  in < SIZE(inst.ingredients);  ++in) {
      reagent& ingredient = inst.ingredients.at(in);
      // Begin transform_names Ingredient Special-cases(ingredient, inst, caller)
      if (is_disqualified(ingredient, inst, caller.name)) continue;
      if (is_numeric_location(ingredient)) numeric_locations_used = true;
      if (is_named_location(ingredient)) names_used = true;
      if (is_integer(ingredient.name)) continue;
      if (!already_transformed(ingredient, names)) {
        raise << maybe(caller.name) << "tried to read ingredient '" << ingredient.name << "' in '" << to_original_string(inst) << "' but it hasn't been written to yet\n" << end();
        // use-before-set Error
        return;
      }
      int v = lookup_name(ingredient, r);
      if (v >= 0) {
        ingredient.set_value(v);
        // Done Placing Ingredient(ingredient, inst, caller)
      }
      else {
        raise << maybe(caller.name) << "can't find a place to store '" << ingredient.name << "'\n" << end();
        return;
      }
    }
    for (int out = 0;  out < SIZE(inst.products);  ++out) {
      reagent& product = inst.products.at(out);
      // Begin transform_names Product Special-cases(product, inst, caller)
      if (is_disqualified(product, inst, caller.name)) continue;
      if (is_numeric_location(product)) numeric_locations_used = true;
      if (is_named_location(product)) names_used = true;
      if (is_integer(product.name)) continue;
      if (names.find(product.name) == names.end()) {
        trace(9993, "name") << "assign " << product.name << " " << curr_idx << end();
        names[product.name] = curr_idx;
        curr_idx += size_of(product);
      }
      int v = lookup_name(product, r);
      if (v >= 0) {
        product.set_value(v);
        // Done Placing Product(product, inst, caller)
      }
      else {
        raise << maybe(caller.name) << "can't find a place to store '" << product.name << "'\n" << end();
        return;
      }
    }
  }
  if (names_used && numeric_locations_used)
    raise << maybe(caller.name) << "mixing variable names and numeric addresses\n" << end();
}

bool is_disqualified(/*mutable*/ reagent& x, const instruction& inst, const string& recipe_name) {
  if (!x.type) {
    raise << maybe(recipe_name) << "missing type for '" << x.original_string << "' in '" << to_original_string(inst) << "'\n" << end();
    // missing-type Error 1
    return true;
  }
  if (is_raw(x)) return true;
  if (is_literal(x)) return true;
  // End is_disqualified Special-cases
  if (x.initialized) return true;
  return false;
}

bool already_transformed(const reagent& r, const map<string, int>& names) {
  return contains_key(names, r.name);
}

int lookup_name(const reagent& r, const recipe_ordinal default_recipe) {
  return Name[default_recipe][r.name];
}

type_ordinal skip_addresses(type_tree* type) {
  while (type && is_compound_type_starting_with(type, "address"))
    type = type->right;
  if (!type) return -1;  // error handled elsewhere
  if (type->atom) return type->value;
  const type_tree* base_type = type;
  // Update base_type in skip_addresses
  if (base_type->atom)
    return base_type->value;
  assert(base_type->left->atom);
  return base_type->left->value;
}

int find_element_name(const type_ordinal t, const string& name, const string& recipe_name) {
  const type_info& container = get(Type, t);
  for (int i = 0;  i < SIZE(container.elements);  ++i)
    if (container.elements.at(i).name == name) return i;
  raise << maybe(recipe_name) << "unknown element '" << name << "' in container '" << get(Type, t).name << "'\n" << end();
  return -1;
}

bool is_numeric_location(const reagent& x) {
  if (is_literal(x)) return false;
  if (is_raw(x)) return false;
  if (x.name == "0") return false;  // used for chaining lexical scopes
  return is_integer(x.name);
}

bool is_named_location(const reagent& x) {
  if (is_literal(x)) return false;
  if (is_raw(x)) return false;
  if (is_special_name(x.name)) return false;
  return !is_integer(x.name);
}

// all names here should either be disqualified or also in bind_special_scenario_names
bool is_special_name(const string& s) {
  if (s == "_") return true;
  if (s == "0") return true;
  // End is_special_name Special-cases
  return false;
}

:(scenario transform_names_supports_containers)
def main [
  x:point <- merge 34, 35
  y:num <- copy 3
]
+name: assign x 1
# skip location 2 because x occupies two locations
+name: assign y 3

:(scenario transform_names_supports_static_arrays)
def main [
  x:@:num:3 <- create-array
  y:num <- copy 3
]
+name: assign x 1
# skip locations 2, 3, 4 because x occupies four locations
+name: assign y 5

:(scenario transform_names_passes_dummy)
# _ is just a dummy result that never gets consumed
def main [
  _, x:num <- copy 0, 1
]
+name: assign x 1
-name: assign _ 1

//: an escape hatch to suppress name conversion that we'll use later
:(scenarios run)
:(scenario transform_names_passes_raw)
% Hide_errors = true;
def main [
  x:num/raw <- copy 0
]
-name: assign x 1
+error: can't write to location 0 in 'x:num/raw <- copy 0'

:(scenarios transform)
:(scenario transform_names_fails_when_mixing_names_and_numeric_locations)
% Hide_errors = true;
def main [
  x:num <- copy 1:num
]
+error: main: mixing variable names and numeric addresses

:(scenario transform_names_fails_when_mixing_names_and_numeric_locations_2)
% Hide_errors = true;
def main [
  x:num <- copy 1
  1:num <- copy x:num
]
+error: main: mixing variable names and numeric addresses

:(scenario transform_names_does_not_fail_when_mixing_names_and_raw_locations)
def main [
  x:num <- copy 1:num/raw
]
-error: main: mixing variable names and numeric addresses
$error: 0

:(scenario transform_names_does_not_fail_when_mixing_names_and_literals)
def main [
  x:num <- copy 1
]
-error: main: mixing variable names and numeric addresses
$error: 0

//:: Support element names for containers in 'get' and 'get-location' and 'put'.
//: (get-location is implemented later)

:(before "End update GET offset_value in Check")
else {
  if (!offset.initialized) {
    raise << maybe(get(Recipe, r).name) << "uninitialized offset '" << offset.name << "' in '" << to_original_string(inst) << "'\n" << end();
    break;
  }
  offset_value = offset.value;
}

:(scenario transform_names_transforms_container_elements)
def main [
  p:&:point <- copy 0
  a:num <- get *p:&:point, y:offset
  b:num <- get *p:&:point, x:offset
]
+name: element y of type point is at offset 1
+name: element x of type point is at offset 0

:(before "End transform_names(inst) Special-cases")
// replace element names of containers with offsets
if (inst.name == "get" || inst.name == "get-location" || inst.name == "put") {
  //: avoid raising any errors here; later layers will support overloading new
  //: instructions with the same names (static dispatch), which could lead to
  //: spurious errors
  if (SIZE(inst.ingredients) < 2)
    break;  // error raised elsewhere
  if (!is_literal(inst.ingredients.at(1)))
    break;  // error raised elsewhere
  if (inst.ingredients.at(1).name.find_first_not_of("0123456789") != string::npos) {
    // since first non-address in base type must be a container, we don't have to canonize
    type_ordinal base_type = skip_addresses(inst.ingredients.at(0).type);
    if (contains_key(Type, base_type)) {  // otherwise we'll raise an error elsewhere
      inst.ingredients.at(1).set_value(find_element_name(base_type, inst.ingredients.at(1).name, get(Recipe, r).name));
      trace(9993, "name") << "element " << inst.ingredients.at(1).name << " of type " << get(Type, base_type).name << " is at offset " << no_scientific(inst.ingredients.at(1).value) << end();
    }
  }
}

:(scenario missing_type_in_get)
% Hide_errors = true;
def main [
  get a, x:offset
]
+error: main: missing type for 'a' in 'get a, x:offset'

//: this test is actually illegal so can't call run
:(scenarios transform)
:(scenario transform_names_handles_containers)
def main [
  a:point <- copy 0/unsafe
  b:num <- copy 0/unsafe
]
+name: assign a 1
+name: assign b 3

//:: Support variant names for exclusive containers in 'maybe-convert'.

:(scenarios run)
:(scenario transform_names_handles_exclusive_containers)
def main [
  12:num <- copy 1
  13:num <- copy 35
  14:num <- copy 36
  20:point, 22:bool <- maybe-convert 12:number-or-point/unsafe, p:variant
]
+name: variant p of type number-or-point has tag 1
+mem: storing 1 in location 22
+mem: storing 35 in location 20
+mem: storing 36 in location 21

:(before "End transform_names(inst) Special-cases")
// convert variant names of exclusive containers
if (inst.name == "maybe-convert") {
  if (SIZE(inst.ingredients) != 2) {
    raise << maybe(get(Recipe, r).name) << "exactly 2 ingredients expected in '" << to_original_string(inst) << "'\n" << end();
    break;
  }
  assert(is_literal(inst.ingredients.at(1)));
  if (inst.ingredients.at(1).name.find_first_not_of("0123456789") != string::npos) {
    // since first non-address in base type must be an exclusive container, we don't have to canonize
    type_ordinal base_type = skip_addresses(inst.ingredients.at(0).type);
    if (contains_key(Type, base_type)) {  // otherwise we'll raise an error elsewhere
      inst.ingredients.at(1).set_value(find_element_name(base_type, inst.ingredients.at(1).name, get(Recipe, r).name));
      trace(9993, "name") << "variant " << inst.ingredients.at(1).name << " of type " << get(Type, base_type).name << " has tag " << no_scientific(inst.ingredients.at(1).value) << end();
    }
  }
}

:(scenario missing_type_in_maybe_convert)
% Hide_errors = true;
def main [
  maybe-convert a, x:variant
]
+error: main: missing type for 'a' in 'maybe-convert a, x:variant'