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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. 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. * 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. * 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. 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.