[PATCH 2/3] selftest/powerpc: Add flags.mk to support pmu buildable

[Michael Ellerman]

Madhavan Srinivasan <maddy at linux.ibm.com> writes:
> When running `make -C powerpc/pmu run_tests` from top level selftests
> directory, currently this error is being reported
>
> make: Entering directory '/home/maddy/linux/tools/testing/selftests/powerpc/pmu'
> Makefile:40: warning: overriding recipe for target 'emit_tests'
> ../../lib.mk:111: warning: ignoring old recipe for target 'emit_tests'
> gcc -m64    count_instructions.c ../harness.c event.c lib.c ../utils.c loop.S  -o /home/maddy/selftest_output//count_instructions
> In file included from count_instructions.c:13:
> event.h:12:10: fatal error: utils.h: No such file or directory
> 12 | #include "utils.h"
>   |          ^~~~~~~~~
> compilation terminated.
>
> This is due to missing of include path in CFLAGS. That is, CFLAGS and
> GIT_VERSION macros are defined in the powerpc/ folder Makefile which
> in this case not involved.
>
> To address the failure incase of executing specific sub-folder test directly,
> a new rule file has been addded by the patch called "flags.mk" under
> selftest/powerpc/ folder and is linked to all the Makefile of powerpc/pmu
> sub-folders.

This patch made my selftest build go from ~10s to ~50s !

I tracked it down to "git describe" being run hundreds of times.

> diff --git a/tools/testing/selftests/powerpc/flags.mk b/tools/testing/selftests/powerpc/flags.mk
> new file mode 100644
> index 000000000000..28374f470126
> --- /dev/null
> +++ b/tools/testing/selftests/powerpc/flags.mk
> @@ -0,0 +1,12 @@
> +#This checks for any ENV variables and add those.
> +
> +#ifeq ($(GIT_VERSION),)
 
This isn't right, # is a comment in make syntax, so this line is just a
comment. It needs to be "ifeq".

> +GIT_VERSION = $(shell git describe --always --long --dirty || echo "unknown")
 
Using '=' here means Make re-runs the command every time the variable is
used. Previously that was OK because the variable was set once and then
exported. But now that it's a Make variable in each file it leads to
"git describe" being run a few hundred times.

I've squashed in those fixes, no need to send a v2.

cheers