tree a9a99c82ec7b9e8fc21261b3102cdd726ccddb79
parent 2290afc2d4419c34fd58f0894670d01cb756ac3c
author Gilles Peskine <Gilles.Peskine@arm.com> 1636405967 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> 1637071217 +0100

PSA operation structures: move less-used fields to the end

Move fields around to have fewer accesses outside the 128-element Thumb
direct access window.

In psa_hkdf_key_derivation_t, move the large fields (output_block, prk,
hmac) after the state bit-fields. Experimentally, it's slightly better
to put hmac last.

In aead_operation_t, tag_length was outside the window. The details depend
on the sizes of contexts included in ctx. Make the large ctx be the last
field.

In mbedtls_psa_hmac_operation_t, the opad field is outside the window when
SHA-512 is enabled. Moving opad before hash_ctx only saves 4 bytes and made
the structure clumsy, so I left it alone.

Results (arm-none-eabi-gcc 7.3.1, build_arm_none_eabi_gcc_m0plus build):
library/psa_crypto.o: 16246 -> 16166 (diff: 80)
library/psa_crypto_aead.o: 952 -> 928 (diff: 24)

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