tree c67c6645e5fb3a7b290e0fae76fcbd08db0cfaf1
parent cfffc28a8066c3364185279013d9611812e4746e
author Gilles Peskine <Gilles.Peskine@arm.com> 1586727808 +0200
committer Gilles Peskine <Gilles.Peskine@arm.com> 1586892228 +0200

Document and fix the MBEDTLS_xxx_ALT logic for the full config

The intended logic around MBEDTLS_xxx_ALT is to exclude them from full
because they require the alternative implementation of one or more
library functions, except that MBEDTLS_PLATFORM_xxx_ALT are different:
they're alternative implementations of a platform function and they
have a built-in default, so they should be included in full. Document
this.

Fix a bug whereby MBEDTLS_PLATFORM_xxx_ALT didn't catch symbols where
xxx contains an underscore. As a consequence,
MBEDTLS_PLATFORM_GMTIME_R_ALT and MBEDTLS_PLATFORM_NV_SEED_ALT are now
enabled in the full config. Explicitly exclude
MBEDTLS_PLATFORM_SETUP_TEARDOWN_ALT because it behaves like the
non-platform ones, requiring an extra build-time dependency.
Explicitly exclude MBEDTLS_PLATFORM_NV_SEED_ALT from baremetal
because it requires MBEDTLS_ENTROPY_NV_SEED, and likewise explicitly
unset it from builds that unset MBEDTLS_ENTROPY_NV_SEED.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>