Lecture 17

• Lecture 17
  • Video
  • Further Improvements
  • Direct Threaded Interpretation
  • Binary Translation

Video

link

Further Improvements

• lookuing up central memory table requires one access and branching, eliminate karna woh

• Every subroutine has same code of extracting instruction and decoding it etc. this is repeatedly done
• so isko predecode karle, decoding before executing

• decode before execution starts and store them in a particular format
• extended opcode and opcode ka combination type maybe
• intermediate representation karra kin dof
• direct thrreaded interpretation

• code array contains instruction ka array
• we directly access dest and src from struct, decode nahi karna
• ab 2 cheeejein hai
  • origginal source
  • predecoded form
  • so 2 program counters
    • TPC
      • intermediate code ke lie
    • SPC
      • source machine code ka
      • instructions nahi a rahe yaha se but still we need it to change or keep track of architecture state

Direct Threaded Interpretation

• predecoded source into intermed form
• instead of storing opcode, store address of subroutine
• ab memory lookup chala gaya and indirect branching bhi fer

• absolute addresses toh depend karenge on runtime..
• so agar dusre system me run karna, toh wapis compile kar

• place offsets instead na wrt base address

• so hamne abhi interpretation dekhlia
  • source code tha, ekek karke dekh rahe instructions
  • inefficient hai

Binary Translation

• interpretation me hamne regs use nahi kie, ham s/w level pe kar rahe the
• take a grp of instructions and do mapping of reg and memory(if reg not available).

• source state thi but target ki nahi dekhi thi hamne interpretation me

• binary translation is logical conclusion of predecoding
• source instruction kko ek predecoded form me laraha tha na mai, now we put directly at target isa level

• we need to map ffrom source state to target state

• Static translations are not always possible
  • someimtes depemndent upon reg values
  • runtime pe pata user input say, so statically kaise karu
  • way code is stored in file(some compiler might store data with code), discoovering that is too difficult, bcz jab tak execute nahi karunga, idk data kis region me hai
  • so dynamic binary translation