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

[Yann E. MORIN]

Pieter, Thomas, All,

On 2020-10-01 09:29 +0200, Pieter De Gendt spake thusly:
> On Wed, Sep 30, 2020 at 9:57 PM Thomas Petazzoni
> <thomas.petazzoni at bootlin.com> wrote:
> > 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
[--SNIP--]
> > 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.
> 
> I understand why you are bothered with completely overriding the configuration,
> however I couldn't think of a workable alternative. There are a lot of
> settings in the
> config.h file. See: https://tls.mbed.org/api/config_8h.html
> 
> Agreed, there are more settings that don't require altering the
> dependency chain,
> but exposing all in buildroot would be a lot of work and hard to maintain?
> 
> Applying tweaks on the custom config also feels a bit awkward, since
> you already
> took the effort of creating the custom config and the "sed" commands might not
> even apply.

But that is what we are doing with the user-provided configuration files
for:
  - uClibc-ng
  - the linux kernel
  - busybox
  - uboot
  - and probably a few others as well...

So it would feel natural that we do the same for mbedtls, so that there
is a consistent behaviour across the board.

Regards,
Yann E. MORIN.

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