[Buildroot] [PATCH 1/1] package/mbedtls: custom configuration file

[Thomas Petazzoni]

Hello Pieter,

Thanks for the proposal. See below for some questions/comments.

On Mon, 28 Sep 2020 11:29:45 +0200
Pieter De Gendt <pieter.degendt at gmail.com> wrote:

> diff --git a/package/mbedtls/mbedtls.mk b/package/mbedtls/mbedtls.mk
> index 5094434e6c..fa74197004 100644
> --- a/package/mbedtls/mbedtls.mk
> +++ b/package/mbedtls/mbedtls.mk
> @@ -68,4 +68,12 @@ else ifeq ($(BR2_microblaze)$(BR2_MIPS_CPU_MIPS32R6)$(BR2_MIPS_CPU_MIPS64R6),y)
>  MBEDTLS_POST_CONFIGURE_HOOKS += MBEDTLS_DISABLE_ASM
>  endif
>  
> +define MBEDTLS_OVERRIDE_CONFIG
> +	cp $(BR2_PACKAGE_MBEDTLS_CUSTOM_CONFIG) $(@D)/include/mbedtls/config.h
> +endef
> +
> +ifneq ($(call qstrip,$(BR2_PACKAGE_MBEDTLS_CUSTOM_CONFIG)),)
> +MBEDTLS_POST_CONFIGURE_HOOKS += MBEDTLS_OVERRIDE_CONFIG
> +endif

We prefer to enclose everything in the conditional block, and do the
qstripping once:

MBEDTLS_CUSTOM_CONFIG = $(call qstrip,$(BR2_PACKAGE_MBEDTLS_CUSTOM_CONFIG))

ifneq ($(MBEDTLS_CUSTOM_CONFIG),)
define MBEDTLS_OVERRIDE_CONFIG
	..
endef
MBEDTLS_POST_CONFIGURE_HOOKS += MBEDTLS_OVERRIDE_CONFIG
endif

However, what bothers me a bit is how it completely overrides all the
configuration logic that takes place before in mbedtls.mk. For example,
if you enable BR2_PACKAGE_MBEDTLS_COMPRESSION=y and use your option to
have a custom configuration file, then what
BR2_PACKAGE_MBEDTLS_COMPRESSION=y does will be ignored.

So, we would have to make BR2_PACKAGE_MBEDTLS_COMPRESSION disappear
when BR2_PACKAGE_MBEDTLS_CUSTOM_CONFIG, but then, how do you bring zlib
as a build dependency of mbedtls ?

We need to decide if the custom configuration file should override all
tweaks, or if all tweaks should be applied on top of the custom
configuration file.

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com