ccache: move environment variables to the configuration file

Move some environment variables to the configuration file, so there's
less happening in the class.

Some changes were made as part of the move:
- max_size was removed so that the per-recipe caches don't grown without
  limit. The default cache is 5GB.
- compiler_check was extended to check both the specs and the version,
  so that a version change that doesn't affect the specs will still mean
  a recompile.

Signed-off-by: Ross Burton <ross.burton@arm.com>
---
 meta/classes/ccache.bbclass | 13 -------------
 meta/conf/ccache.conf       | 15 +++++++++++++--
 2 files changed, 13 insertions(+), 15 deletions(-)

On Wed, Jul 16, 2025 at 2:50 AM Ross Burton via lists.openembedded.org
<ross.burton=arm.com@lists.openembedded.org> wrote:
>
> Move some environment variables to the configuration file, so there's
> less happening in the class.
>
> Some changes were made as part of the move:
> - max_size was removed so that the per-recipe caches don't grown without
>   limit. The default cache is 5GB.
> - compiler_check was extended to check both the specs and the version,
>   so that a version change that doesn't affect the specs will still mean
>   a recompile.
>
> Signed-off-by: Ross Burton <ross.burton@arm.com>
> ---
>  meta/classes/ccache.bbclass | 13 -------------
>  meta/conf/ccache.conf       | 15 +++++++++++++--
>  2 files changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/meta/classes/ccache.bbclass b/meta/classes/ccache.bbclass
> index 2d6a3ea7229..5ce23e50f34 100644
> --- a/meta/classes/ccache.bbclass
> +++ b/meta/classes/ccache.bbclass
> @@ -42,23 +42,10 @@ CCACHE_NATIVE_RECIPES_ALLOWED ?= ""
>  # in different builds.
>  export CCACHE_BASEDIR ?= "${TMPDIR}"
>
> -# Used for sharing cache files after compiler is rebuilt
> -export CCACHE_COMPILERCHECK ?= "%compiler% -dumpspecs"
> -
>  export CCACHE_CONFIGPATH ?= "${COREBASE}/meta/conf/ccache.conf"
>
>  export CCACHE_DIR ?= "${CCACHE_TOP_DIR}/${MULTIMACH_TARGET_SYS}/${PN}"
>
> -# Fixed errors:
> -# ccache: error: Failed to create directory /run/user/0/ccache-tmp: Permission denied
> -export CCACHE_TEMPDIR ?= "${CCACHE_DIR}/tmp"
> -
> -# We need to stop ccache considering the current directory or the
> -# debug-prefix-map target directory to be significant when calculating
> -# its hash. Without this the cache would be invalidated every time
> -# ${PV} or ${PR} change.
> -export CCACHE_NOHASHDIR ?= "1"
> -
>  python() {
>      """
>      Enable ccache for the recipe
> diff --git a/meta/conf/ccache.conf b/meta/conf/ccache.conf
> index 499e5327b8c..ea658708a1f 100644
> --- a/meta/conf/ccache.conf
> +++ b/meta/conf/ccache.conf
> @@ -1,7 +1,18 @@
> -max_size = 0
> -
>  # Avoid spurious cache misses caused by recipe sysroot creation: Creating a
>  # recipe sysroot hardlinks all dependent files into place. Hardlinking updates
>  # the file's ctime which in turn interferes with ccache's include_file_ctime
>  # check.
>  sloppiness = include_file_ctime
> +
> +# Only rebuild if the compiler version or specs have changed, as we rebuild
> +# compilers more than is usual.
> +compiler_check = %compiler% -dumpversion; %compiler% -dumpspecs

-dumpspecs is very gcc centric option and clang does not support it,
previously we overwrote CCACHE_COMPILERCHECK
in clang bbclass to something like %compiler% -v, how do we get
that parity with this approach ?

> +
> +# We need to stop ccache considering the current directory or the
> +# debug-prefix-map target directory to be significant when calculating
> +# its hash. Without this the cache would be invalidated every time
> +# ${PV} or ${PR} change.
> +hash_dir = false
> +
> +# If ccache runs under pseudo it will try to create files in /run/user/0/ccahe-tmp
> +temporary_dir = $CCACHE_DIR/tmp
> --
> 2.43.0
>
>
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On 17 Jul 2025, at 02:23, Khem Raj <raj.khem@gmail.com> wrote:
>> +# Only rebuild if the compiler version or specs have changed, as we rebuild
>> +# compilers more than is usual.
>> +compiler_check = %compiler% -dumpversion; %compiler% -dumpspecs
> 
> -dumpspecs is very gcc centric option and clang does not support it,
> previously we overwrote CCACHE_COMPILERCHECK
> in clang bbclass to something like %compiler% -v, how do we get
> that parity with this approach ?

Ah.  I’ll drop that change for now.

Maybe we should just check the version and leave it at that?

Ross

On Thu, Jul 17, 2025 at 5:14 AM Ross Burton <Ross.Burton@arm.com> wrote:
>
> On 17 Jul 2025, at 02:23, Khem Raj <raj.khem@gmail.com> wrote:
> >> +# Only rebuild if the compiler version or specs have changed, as we rebuild
> >> +# compilers more than is usual.
> >> +compiler_check = %compiler% -dumpversion; %compiler% -dumpspecs
> >
> > -dumpspecs is very gcc centric option and clang does not support it,
> > previously we overwrote CCACHE_COMPILERCHECK
> > in clang bbclass to something like %compiler% -v, how do we get
> > that parity with this approach ?
>
> Ah.  I’ll drop that change for now.
>
> Maybe we should just check the version and leave it at that?

My hunch is that using
CCACHE_COMPILERCHECK=content
should be good and it will be faster than trying to find the version of compiler
because it will do gcc -v or clang -v for every compiler invocation which could
more expensive than doing a checksum on compiler binary content.

>
> Ross