Chapter 17: Assembly Basics and Calling Conventions

Vol 3: Computer Core Expedition · Chapter 17

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Metadata Card

Attribute	Value
Keywords	ABI, Registers, Calling Conventions, Stack Frames, Inline Assembly

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Your Progress

"Assembly reveals the true nature of CPU execution. Every C statement, every function call, every variable access — all become explicit register operations and memory accesses."

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Encounter 1: RISC-V Registers

Name	Usage
x0 (zero)	Always zero
x1 (ra)	Return address
x2 (sp)	Stack pointer
x3 (gp)	Global pointer
x5-x7, x28-x31 (t0-t6)	Temporaries
x8-x9, x18-x27 (s0-s11)	Saved registers
x10-x17 (a0-a7)	Function arguments / return values

Encounter 2: Calling Convention

1. Caller saves any temporaries needed after the call
2. Arguments in a0-a7
3. jal jumps to function, saves return address in ra
4. Callee saves s0-s11 it will use
5. Callee adjusts sp for local variables
6. Return value in a0
7. Callee restores sp, s0-s11, then ret

Encounter 3: Stack Frame Structure

High addresses
    ... (caller's frame)
    return address (ra)
    saved s0
    local variables
    argument build area
SP → (empty for next call)
Low addresses

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Verification Checklist

• [ ] Can identify common RISC-V registers
• [ ] Can describe the calling convention (who saves what)
• [ ] Can draw a stack frame diagram
• [ ] Can read basic RISC-V assembly

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Chapter 18: Performance Engineering