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Note that application code needs PSA_WANT_xxx too

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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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Gilles Peskine 2020-11-16 12:04:40 +01:00
parent 1b1f3fb96d
commit 198024cd02
1 changed files with 2 additions and 2 deletions
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docs/proposed/psa-conditional-inclusion-c.md
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@ -5,7 +5,7 @@ This document is a proposed interface for deciding at build time which cryptogra
This is currently a proposal for Mbed TLS. It is not currently on track for standardization in PSA.
Time-stamp: "2020/11/16 11:00:23 GMT"
Time-stamp: "2020/11/16 11:04:35 GMT"
## Introduction
@ -119,7 +119,7 @@ These symbols are not part of the public interface of Mbed TLS towards applicati
When `MBEDTLS_PSA_CRYPTO_CONFIG` is set, the header file `mbedtls/config.h` needs to define all the `MBEDTLS_xxx_C` configuration symbols, including the ones deduced from the PSA Crypto configuration. It does this by including the new header file **`mbedtls/config_psa.h`**, which defines the `MBEDTLS_PSA_BUILTIN_xxx` symbols and deduces the corresponding `MBEDTLS_xxx_C` (and other) symbols.
When `MBEDTLS_PSA_CRYPTO_CONFIG` is not set, the configuration of Mbed TLS works as before, and the inclusion of non-PSA code only depends on `MBEDTLS_xxx` symbols defined (or not) in `mbedtls/config.h`. In this case, `mbedtls/config_psa.h` deduces PSA configuration symbols (`PSA_WANT_xxx`, `MBEDTLS_PSA_BUILTIN_xxx`) from classic configuration symbols (`MBEDTLS_xxx`). The definitions in `mbedtls/config_psa.h` are only needed to build the PSA parts of the library and code that uses these parts. Note that `psa/crypto_struct.h` and `psa/crypto_sizes.h` include definitions that depend on the configuration, so `mbedtls/config_psa.h` needs to be included in or before these headers (it isn't enough to include it only from files in `library`).
When `MBEDTLS_PSA_CRYPTO_CONFIG` is not set, the configuration of Mbed TLS works as before, and the inclusion of non-PSA code only depends on `MBEDTLS_xxx` symbols defined (or not) in `mbedtls/config.h`. In this case, `mbedtls/config_psa.h` deduces PSA configuration symbols (`PSA_WANT_xxx`, `MBEDTLS_PSA_BUILTIN_xxx`) from classic configuration symbols (`MBEDTLS_xxx`). The `PSA_WANT_xxx` definitions in `mbedtls/config_psa.h` are needed not only to build the PSA parts of the library, but also to build code that uses these parts. This includes structure definitions in `psa/crypto_struct.h`, size calculations in `psa/crypto_sizes.h`, and application code that contains code that's specific to a given cryptographic mechanism (which is reflected in Mbed TLS in code under `MBEDTLS_USE_PSA_CRYPTO` and in conditional compilation guards in tests and sample programs).
`mbedtls/config_psa.h` includes two header files: