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//: Labels are defined by ending names with a ':'. This layer will compute
//: addresses for labels, and compute the offset for instructions using them.
:(scenarios transform)
:(scenario map_label)
== 0x1
# instruction effective address operand displacement immediate
# op subop mod rm32 base index scale r32
# 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
loop:
05 0x0d0c0b0a/imm32 # add to EAX
+translate: label 'loop' is at address 1
:(before "End One-time Setup")
Transform.push_back(replace_labels);
:(code)
void replace_labels(program& p) {
if (p.segments.empty()) return;
segment& code = p.segments.at(0);
map<string, uint32_t> address;
compute_addresses_for_labels(code, address);
if (trace_contains_errors()) return;
drop_labels(code);
if (trace_contains_errors()) return;
replace_labels_with_addresses(code, address);
}
void compute_addresses_for_labels(const segment& code, map<string, uint32_t> address) {
int current_byte = 0;
for (int i = 0; i < SIZE(code.lines); ++i) {
const line& inst = code.lines.at(i);
for (int j = 0; j < SIZE(inst.words); ++j) {
const word& curr = inst.words.at(j);
// hack: if we have any operand metadata left after previous transforms,
// deduce its size
// Maybe we should just move this transform to before instruction
// packing, and deduce the size of *all* operands. But then we'll also
// have to deal with bitfields.
if (has_metadata(curr, "disp32") || has_metadata(curr, "imm32")) {
if (*curr.data.rbegin() == ':')
raise << "'" << to_string(inst) << "': don't use ':' when jumping to labels\n" << end();
current_byte += 4;
}
// automatically handle /disp8 and /imm8 here
else if (*curr.data.rbegin() != ':') {
++current_byte;
}
else {
if (contains_any_operand_metadata(curr))
raise << "'" << to_string(inst) << "': label definition (':') not allowed in operand\n" << end();
if (j > 0)
raise << "'" << to_string(inst) << "': labels can only be the first word in a line.\n" << end();
string label = curr.data.substr(0, SIZE(curr.data)-1);
put(address, label, current_byte);
trace(99, "translate") << "label '" << label << "' is at address " << (current_byte+code.start) << end();
// no modifying current_byte; label definitions won't be in the final binary
}
}
}
}
void drop_labels(segment& code) {
for (int i = 0; i < SIZE(code.lines); ++i) {
line& inst = code.lines.at(i);
remove_if(inst.words.begin(), inst.words.end(), is_label);
}
}
bool is_label(const word& w) {
return *w.data.rbegin() == ':';
}
void replace_labels_with_addresses(const segment& code, map<string, uint32_t> address) {
}
//: Label definitions must be the first word on a line. No jumping inside
//: instructions.
//: They should also be the only word on a line.
//: However, you can absolutely have multiple labels map to the same address,
//: as long as they're on separate lines.
:(scenario multiple_labels_at)
== 0x1
# instruction effective address operand displacement immediate
# op subop mod rm32 base index scale r32
# 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
loop:
loop2:
05 0x0d0c0b0a/imm32 # add to EAX
loop3:
f
+translate: label 'loop' is at address 1
+translate: label 'loop2' is at address 1
+translate: label 'loop3' is at address 6
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