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Move non-normative parts of "A" extensions (atomics) into NOTE block #1822

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Jan 25, 2025
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Move non-normative parts of "A" extensions (atomics) into NOTE block #1822

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0f21952
a-st-ext: mark examples as a note
radimkrcmar Jan 23, 2025
eccfc4f
a-st-ext: remove manual page breaks
radimkrcmar Jan 23, 2025
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13 changes: 6 additions & 7 deletions src/a-st-ext.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -227,8 +227,8 @@ instruction unless the _rl_ bit is also set. LR._rl_ and SC._aq_
instructions are not guaranteed to provide any stronger ordering than
those with both bits clear, but may result in lower performance.

<<<

[NOTE]
====
[[cas]]
[source,asm]
.Sample code for compare-and-swap function using LR/SC.
Expand All @@ -250,6 +250,7 @@ those with both bits clear, but may result in lower performance.
LR/SC can be used to construct lock-free data structures. An example
using LR/SC to implement a compare-and-swap function is shown in
<<cas>>. If inlined, compare-and-swap functionality need only take four instructions.
====
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[[sec:lrscseq]]
=== Eventual Success of Store-Conditional Instructions
Expand Down Expand Up @@ -434,15 +435,15 @@ both imply additional unnecessary ordering as compared to AMOs with the
corresponding _aq_ or _rl_ bit set.
====

[NOTE]
====
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An example code sequence for a critical section guarded by a
test-and-test-and-set spinlock is shown in
Example <<critical>>. Note the first AMO is marked _aq_ to
order the lock acquisition before the critical section, and the second
AMO is marked _rl_ to order the critical section before the lock
relinquishment.

<<<

[[critical]]
[source,asm]
.Sample code for mutual exclusion. `a0` contains the address of the lock.
Expand All @@ -457,9 +458,7 @@ relinquishment.
# ...
amoswap.w.rl x0, x0, (a0) # Release lock by storing 0.

[NOTE]
====
We recommend the use of the AMO Swap idiom shown above for both lock
We recommend the use of the AMO Swap idiom shown in <<critical>> for both lock
acquire and release to simplify the implementation of speculative lock
elision. cite:[Rajwar:2001:SLE]
====
Expand Down
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