[XEN,0/3] build: reduce number of $(shell) execution on make 4.4

Message

Anthony PERARD June 21, 2023, 4:19 p.m. UTC

Patch series available in this git branch:
https://xenbits.xen.org/git-http/people/aperard/xen-unstable.git br.build-exported-shell-command-value-v1

With GNU make 4.4, the number of execution of the command present in $(shell )
in exported variables increased greatly. This is probably because as of make
4.4, exported variable are also added to the environment of $(shell )
construct.

From the annoncement:

    https://lists.gnu.org/archive/html/info-gnu/2022-10/msg00008.html
    > * WARNING: Backward-incompatibility!
    >   Previously makefile variables marked as export were not exported to commands
    >   started by the $(shell ...) function.  Now, all exported variables are
    >   exported to $(shell ...).  If this leads to recursion during expansion, then
    >   for backward-compatibility the value from the original environment is used.
    >   To detect this change search for 'shell-export' in the .FEATURES variable.

Also, there's a new paragraph in the GNU make manual, but it's a warning about
exporting all variable, still it might be relevant to the new observed
behavior:

    https://www.gnu.org/software/make/manual/make.html#Variables_002fRecursion
    > Adding a variable’s value to the environment requires it to be expanded. If
    > expanding a variable has side-effects (such as the info or eval or similar
    > functions) then these side-effects will be seen every time a command is
    > invoked.

The issue was reported on IRC by jandryuk.

So, I've locate a few obvious candidate to fix, maybe there's more $(shell) to
change?

Anthony PERARD (3):
  build: define ARCH and SRCARCH later
  build: evaluate XEN_BUILD_* and XEN_DOMAIN on first use
  Config.mk: evaluate XEN_COMPILE_ARCH and XEN_OS on first use

 Config.mk    |  6 +++---
 xen/Makefile | 21 +++++++++++----------
 2 files changed, 14 insertions(+), 13 deletions(-)