[Buildroot] ccache dependency issues

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear Thomas De Schampheleire,

On Thu, 1 Aug 2013 12:08:30 +0200, Thomas De Schampheleire wrote:

> >> What do you think of this solution?
> >
> > This indeed looks like a much better solution. I think it would be even
> > better if host-ccache was moved from BASE_TARGETS to
> > DEPENDENCIES_HOST_PREREQ. I.e, the main Makefile chunk
> >
> > ifeq ($(BR2_CCACHE),y)
> > BASE_TARGETS += host-ccache
> > endif
> >
> > would be moved to support/dependencies/dependencies.mk as:
> >
> > ifeq ($(BR2_CCACHE),y)
> > DEPENDENCIES_HOST_PREREQ += host-ccache
> > endif
> >
> > and then we can also remove the usage of HOSTCC_NOCCACHE from
> > package/ccache/ccache.mk.
> >
> > This way, all the package that should not rely on ccache availability
> > are built as part of the 'dependencies' target, and as soon as we enter
> > $(BASE_TARGETS), we now that we have ccache available.
> 
> We will have to start expressing some dependencies between
> dependencies, I think: in order to build ccache, the package has to be
> extracted, but for this one would need host-tar (or host-xzcat for
> example).
> 
> This could be done by creating an order in which
> support/dependencies/check-host-X.mk is included, so that
> DEPENDENCIES_HOST_PREREQ is filled in a fixed order.
> Alternatively, if we make an assumption that we only need such
> dependencies on extract-tools (like tar, xzcat) then we can introduce
> another level of dependencies.
> Yet another alternative is to explicitly express the dependencies like:
> host-ccache: host-tar
> but this is cumbersome, and should also take into account the outcome
> of suitable-host-package.

I believe we don't have to worry about this for now. The
dependencies.mk code looks like this (with ccache added as proposed):

define suitable-host-package
$(shell support/dependencies/check-host-$(1).sh $(2))
endef
-include support/dependencies/check-host-*.mk

ifeq ($(BR2_STRIP_sstrip),y)
DEPENDENCIES_HOST_PREREQ+=host-sstrip
endif

ifeq ($(BR2_CCACHE),y)
DEPENDENCIES_HOST_PREREQ+=host-ccache
endif

So the dependencies such as host-tar and host-xzcat are always pulled
before host-sstrip and host-ccache, so we should be all set. For sure,
this is the case because we don't do top-level parallel build, but
there are already many places in Buildroot that rely on ordering of
dependencies.

> > Does executing cpp through ccache makes sense? For now, HOSTCPP is
> > always 'cpp', regardless of whether ccache is enabled or not, so there
> > should not be any problem.
> 
> Ah, sorry, my mistake. cpp is the pre-processor but I was confusing it with g++
> (very bad naming IMO: the acronym CPP is also often used in the
> context of the C++ language)

Right.

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com