ptrdiff_t Assembler::LinkAndGetOffsetTo(BufferOffset branch, Label* label) {
if (armbuffer_.oom())
return js::jit::LabelBase::INVALID_OFFSET;
if (label->bound()) {
// The label is bound: all uses are already linked.
ptrdiff_t branch_offset = ptrdiff_t(branch.getOffset() / element_size);
ptrdiff_t label_offset = ptrdiff_t(label->offset() / element_size);
return label_offset - branch_offset;
}
if (!label->used()) {
// The label is unbound and unused: store the offset in the label itself
// for patching by bind().
label->use(branch.getOffset());
return js::jit::LabelBase::INVALID_OFFSET;
}
// The label is unbound but used. Create an implicit linked list between
// the branches, and update the linked list head in the label struct.
ptrdiff_t prevHeadOffset = static_cast<ptrdiff_t>(label->offset());
label->use(branch.getOffset());
VIXL_ASSERT(prevHeadOffset - branch.getOffset() != js::jit::LabelBase::INVALID_OFFSET);
return prevHeadOffset - branch.getOffset();
}
void MozBaseAssembler::WritePoolGuard(BufferOffset branch, Instruction* inst, BufferOffset dest) {
int byteOffset = dest.getOffset() - branch.getOffset();
VIXL_ASSERT(byteOffset % kInstructionSize == 0);
int instOffset = byteOffset >> kInstructionSizeLog2;
Assembler::b(inst, instOffset);
}
static ptrdiff_t
EncodeOffset(BufferOffset cur, BufferOffset next)
{
MOZ_ASSERT(next.assigned() && cur.assigned());
ptrdiff_t offset = next.getOffset() - cur.getOffset();
MOZ_ASSERT(offset % kInstructionSize == 0);
return offset / kInstructionSize;
}
// A common implementation for the LinkAndGet<Type>OffsetTo helpers.
//
// If the label is bound, returns the offset as a multiple of 1 << elementShift.
// Otherwise, links the instruction to the label and returns the raw offset to
// encode. (This will be an instruction count.)
//
// The offset is calculated by aligning the PC and label addresses down to a
// multiple of 1 << elementShift, then calculating the (scaled) offset between
// them. This matches the semantics of adrp, for example. (Assuming that the
// assembler buffer is page-aligned, which it probably isn't.)
//
// For an unbound label, the returned offset will be encodable in the provided
// branch range. If the label is already bound, the caller is expected to make
// sure that it is in range, and emit the necessary branch instrutions if it
// isn't.
//
ptrdiff_t
MozBaseAssembler::LinkAndGetOffsetTo(BufferOffset branch, ImmBranchRangeType branchRange,
unsigned elementShift, Label* label)
{
if (armbuffer_.oom())
return kEndOfLabelUseList;
if (label->bound()) {
// The label is bound: all uses are already linked.
ptrdiff_t branch_offset = ptrdiff_t(branch.getOffset() >> elementShift);
ptrdiff_t label_offset = ptrdiff_t(label->offset() >> elementShift);
return label_offset - branch_offset;
}