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x86-64 Assembly / Functions & ABI

Callee-saved registers

Learn Callee-saved registers in x86-64 Assembly through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Intermediate

Callee-saved registers is an atomic x86-64 Assembly topic inside Functions & ABI. This lesson focuses on how the Callee-saved registers construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for Callee-saved registers, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.

Topic-specific example

assembly-06-07-callee-saved-registers.asm
assembly Try It Live 
worker:
push rbx
mov rbx,rdi
; use RBX
pop rbx
ret
Edge case / engineering note

For Callee-saved registers, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

Callee-saved registers Mastery Check →
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Return value RAX
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Stack alignment