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Add note on platform-specific barriers

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Describe the approach of platform-specific code and draw a comparison
with the constant-time module.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
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David Horstmann 2023-10-30 17:13:54 +00:00
parent e045b55c65
commit 15b5beea0c
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docs/architecture/psa-shared-memory.md
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@ -245,7 +245,7 @@ Once the copying code is implemented, it should be evaluated to see whether comp
If copying behaviour is preserved by all major compilers then assume that compiler optimization is not a problem.
If copying behaviour is optimized away by the compiler, further investigation is needed. Experiment with using the `volatile` keyword to force the compiler not to optimize accesses to the copied buffers.
If copying behaviour is optimized away by the compiler, further investigation is needed. Experiment with using the `volatile` keyword to force the compiler not to optimize accesses to the copied buffers. If the `volatile` keyword is not sufficient, we may be able to use compiler or target-specific techniques to prevent optimization, for example memory barriers or empty `asm` blocks. These may be implemented and verified for important platforms while retaining a C implementation that is likely to be correct on most platforms as a fallback - the same approach taken by the constant-time module.
**Open questions: Will the compiler optimize away copies? If so, can it be prevented from doing so in a portable way?**