void
AsmJSProfilingFrameIterator::initFromFP(const AsmJSActivation &activation)
{
uint8_t *fp = activation.fp();
// If a signal was handled while entering an activation, the frame will
// still be null.
if (!fp) {
JS_ASSERT(done());
return;
}
// Since we don't have the pc for fp, start unwinding at the caller of fp,
// whose pc we do have via fp->returnAddress. This means that the innermost
// frame is skipped but this is fine because:
// - for FFI calls, the innermost frame is a thunk, so the first frame that
// shows up is the function calling the FFI;
// - for Math and other builtin calls, when profiling is activated, we
// patch all call sites to instead call through a thunk; and
// - for interrupts, we just accept that we'll lose the innermost frame.
void *pc = ReturnAddressFromFP(fp);
const AsmJSModule::CodeRange *codeRange = module_->lookupCodeRange(pc);
JS_ASSERT(codeRange);
codeRange_ = codeRange;
stackAddress_ = fp;
switch (codeRange->kind()) {
case AsmJSModule::CodeRange::Entry:
callerPC_ = nullptr;
callerFP_ = nullptr;
break;
case AsmJSModule::CodeRange::Function:
fp = CallerFPFromFP(fp);
callerPC_ = ReturnAddressFromFP(fp);
callerFP_ = CallerFPFromFP(fp);
AssertMatchesCallSite(*module_, codeRange, callerPC_, callerFP_, fp);
break;
case AsmJSModule::CodeRange::IonFFI:
case AsmJSModule::CodeRange::SlowFFI:
case AsmJSModule::CodeRange::Interrupt:
case AsmJSModule::CodeRange::Inline:
case AsmJSModule::CodeRange::Thunk:
MOZ_CRASH("Unexpected CodeRange kind");
}
// Since, despite the above reasoning for skipping a frame, we do want FFI
// trampolines and interrupts to show up in the profile (so they can
// accumulate self time and explain performance faults), an "exit reason" is
// stored on all the paths leaving asm.js and the iterator logic treats this
// reason as its own frame. If we have exited asm.js code without setting an
// exit reason, the reason will be None and this means the code was
// asynchronously interrupted.
exitReason_ = activation.exitReason();
if (exitReason_ == AsmJSExit::None)
exitReason_ = AsmJSExit::Interrupt;
JS_ASSERT(!done());
}
