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Tweak compiler optimization evaluation section

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* Remove references to the platform - this is unlikely to affect whether
copies are optimized.
* Note that the evaluation should test extreme optimisation settings.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
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David Horstmann 2023-10-20 18:14:36 +01:00
parent 4e54abf182
commit 17b3716c5a
1 changed files with 3 additions and 3 deletions
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docs/architecture/psa-shared-memory.md
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@ -238,12 +238,12 @@ Copy what needs copying. This is broadly straightforward, however there are a fe
It is unclear whether the compiler will attempt to optimize away copying operations.
Once the copying code is implemented, it should be evaluated to see whether compiler optimization is a problem. Specifically, for the major compilers and platforms supported by Mbed TLS:
Once the copying code is implemented, it should be evaluated to see whether compiler optimization is a problem. Specifically, for the major compilers supported by Mbed TLS:
* Write a small program that uses a PSA function which copies inputs or outputs.
* Build the program with link-time optimization / full-program optimization enabled (e.g. `-flto` with `gcc`).
* Build the program with link-time optimization / full-program optimization enabled (e.g. `-flto` with `gcc`). Try also enabling the most extreme optimization options such as `-Ofast` (`gcc`) and `-Oz` (`clang`).
* Inspect the generated code with `objdump` or a similar tool to see if copying operations are preserved.
If copying behaviour is preserved by all major compilers and platforms then assume that compiler optimization is not a problem.
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.