#cs240

Location : N'dah Hall, Shah Alam. Date: 25th May 2016 Time: 8.30 PM - 11.30 PM

Supposed it's a celebration pre-graduation dinner for seniors only but since the president of our club said "IT'S A COMPULSORY FOR PART 3 STUDENT TO JOIN THE EVENT!" anddd we here to celebrate part 6 senior of our course. The cost that we paid around RM50 and all my classmates were like "Wow, why it's soo expensive I mean like back then from our campus, we didn't have to pay at all! *with angry faces* " Well from my campus Jasin, to pay for dinner fee sometimes exceed RM50 so we didn't even surprise if we have to pay it that much cost. And so at the beginning of the dinner, it's quite boring and only our class for part 3 had attended this event. It's kinda awkward because we don't even recognise the seniors and so do they. So no conversation with the seniors, at all. We just talked among our class, take some pictures and "syok sendiri" hahaha. But i mean not every senior I don't recognise, I know Luqmanul Hakim a.k.a Bob haha, since he's my senior from SM Teknik Shah Alam and we even from the same course. I didn't know that he's so famous here because back then he's just a quiet person. Well, time changes people.

Heap memory safety

All local pointers point to the SIP’s heap

Pointers only come from SIP’s trusted memory allocator

Pointers are strongly typed

Exchange heap memory safety

EH pointers obey linear type discipline

No double access

Strongly typed

Channel contract agreement

Need to verify that both ends of a channel agree on the channel contract

Kernel ABI agreement

Instruction safety: can’t use privileged instructions inappropriately.

Channel contracts checked for unhanded messages

Channel contracts need all cycles in contract states to contain at least one receive and one send action.

Basically avoid A sending infinite messages to B without waiting for response. This can overflow buffer.

At SIP install time, verifier checks the byte code (byte code in MSIL).

Alternatives: message copying or kernel buffering. Performance not a convincing reason to use exchange heaps—micro benchmarks != application performance.

Kernel responsible for managing the exchange heap’s memory:

It GC’s the exchange heap to eliminate objects held by exited SIPs. 

Singularity also prevents processes from simultaneously accessing objects in shared memory. 

Exchange heap explicitly designed for IPC. 

Linear type discipline for exchange heap objects. 

Each process can have at most one pointer to an exchange heap object at a time. When a process sends a message, the type of the send “system call” forces the sending process to lose that sole pointer to the message. 

Each exchange heap object is accessible to at most one process at a time. 

Sing# is a garbage collected language

Each process has page-disjoint heap. Why?

No shared memory (easy verification)

Simple accounting: memory size == page count

Simple recovery after process exit. Just reclaim all pages for garbage collect.

Simplify experiments with address space designs. what?

Evaluating Hardware Isolation Levels

You can use Singularity to evaluate levels of hardware isolation:

No runtime checks (bounds checks, null pointer checks).

Physical memory: default Singularity; segmentation no paging.

Add 4KB Pages: turn on paging.

Add separate domain: separate duplicate page table for application process, context switches require register %lcr3.

Add ring 3: give application process user privilege. Context switches require protected control transfer (syscall/interrupts).

Software Isolated Processes

Processes run in same address space as kernel, isolated by software only.

Why not use hardware? Performance (kernel crossings are expensive).

Don’t need hardware virtual memory if you have a memory-safe language. Hardware VM needs TLB. TLB has extra cost.