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x86-64 Assembly / Loops & Arrays

REP MOVSB

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

10 min read • Intermediate

REP MOVSB is an atomic x86-64 Assembly topic inside Loops & Arrays. This lesson focuses on how the REP MOVSB construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for REP MOVSB, 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-05-10-rep-movsb.asm
assembly Try It Live 
lea rsi,[rel src]
lea rdi,[rel dst]
mov rcx,5
cld
rep movsb
section .data
src db 'hello'
dst times 5 db 0
Edge case / engineering note

For REP MOVSB, 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

REP MOVSB Mastery Check →
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