Alias in Storage Allocation

• Program data can be stored in memory in 2 ways:

  • Storage in global area
    • memory pages are allocated statically, i.e. all data is put at a fixed (virtual) address at load time
    • loading such data takes often 2 instructions, since the load immediate instruction in MIPS is limited by 64 KB offset: ldadr R1,addr #load base pointer
    • ldw R2,R1+offset #load base+offset
    • COMMON block data, global data, SAVE data, malloc, mmap
    • compilation with -static: all variables are allocated in global area
  • Storage on the stack
    • memory pages are allocated dynamically during program exec
    • each subroutine gets new stack area for local data
    • loading data from the stack requires single instruction ldw R2,TOS+offset #load TopOfStack+offset
    • local (automatic) variables, temporary storage, alloca data
  • Routines called from a parallel region :
    • Allocate private stack area
    • Variables allocated on private stack are private.
    • Variables in global area are shared (aliases).

Previous slide

Next slide

Back to first slide

View graphic version