Sunday, November 29, 2009

Bouquet of questions-2

o What is a bus error?

Bus refers to address bus and an error means passing an illegal address to the address bus. There are two signals that can be sent by kernel for an illegal address:

A SIGBUS is issued for an obvious wrong virtual address, there is no address translation and CPU can outright say that address is bogus.

SIGSEGV is issued when after translating the address, CPU realizes that address is bogus.

SIGBUS is always better since it avoids address translation. But which signal to issue, depends on CPU.

o What will be the output?

int a[10];
printf("%d", sizeof(a);

Friday, November 6, 2009

Bouquet of questions

o What is a cache line?

- Smallest unit of data transfer between cache and main memory.
- Finest level of granularity

o How can I get IPC information over processes?

- Use $ipcs

o Tell the value of enum's elements.

enum e_tag{ a, b, c, d=20, e, f, g=20, h

- a=0, b=1, c=3, d=20, e=21, f=22, g=20, h=21

o Why use volatile?

- To avoid compiler optimization on variables involved in two cases:
+ Shared library
+ Value updated implicitly by hardware

Avoid optimization of Load/Store instructions by the compiler.
e.g., If you have a variable(X) that reads from a shared lib variable(Y), while Y is being updated by other process. Compiler would have no idea of this dependency of external value updates and it may remove these LOAD/STORE instructions during compilation.