Hello,
I try to understand what happens in this code:
When you call something you are writing:
__ Call(builtin, RelocInfo::CODE_TARGET);
What how it looks:
void MacroAssembler::Call(Handle<Code> code_object,
RelocInfo::Mode rmode,
TypeFeedbackId ast_id) {
#ifdef DEBUG
int end_position = pc_offset() + CallSize(code_object);
#endif
DCHECK(RelocInfo::IsCodeTarget(rmode) ||
rmode == RelocInfo::CODE_AGE_SEQUENCE);
call(code_object, rmode, ast_id);
#ifdef DEBUG
CHECK_EQ(end_position, pc_offset());
#endif
}
Then you go to call(code_object, rmode, ast_id);
void Assembler::call(Handle<Code> target,
RelocInfo::Mode rmode,
TypeFeedbackId ast_id) {
positions_recorder()->WriteRecordedPositions();
EnsureSpace ensure_space(this);
// 1110 1000 #32-bit disp.
emit(0xE8);
emit_code_target(target, rmode, ast_id);
}
Finally:
void Assembler::emit_code_target(Handle<Code> target,
RelocInfo::Mode rmode,
TypeFeedbackId ast_id) {
DCHECK(RelocInfo::IsCodeTarget(rmode) ||
rmode == RelocInfo::CODE_AGE_SEQUENCE);
if (rmode == RelocInfo::CODE_TARGET && !ast_id.IsNone()) {
RecordRelocInfo(RelocInfo::CODE_TARGET_WITH_ID, ast_id.ToInt());
} else {
RecordRelocInfo(rmode);
}
int current = code_targets_.length();
if (current > 0 && code_targets_.last().is_identical_to(target)) {
// Optimization if we keep jumping to the same code target.
emitl(current - 1);
} else {
code_targets_.Add(target);
emitl(current);
}
}
I understand all code besides one things:
int current = code_targets_.length();
emitl(current);
We write index of code object in code_targets, why we don't write address
to object directly?
I grep the code and I've not find appropriate using of code_targets.
But with --print_code I can see that v8 generates call by address, not a
index.
Do you know where v8 translates index from code_targets to appropriate
address?
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