tools build: Fix feature detection output due to eval expansion

As the first eval expansion is used only to generate Makefile statements,
messages should not be displayed at this stage, as for example conditional
expressions are not evaluated.

It can be seen for example in the output of feature detection for bpftool,
where the number of detected features does not change, despite turning on
the verbose mode (VF = 1) and there are additional features to display.

Fix this issue by escaping the $ before $(info) statements, to ensure that
messages are printed only when the function containing them is actually
executed, and not when it is expanded.

In addition, move the $(info) statement out of feature_print_status, due to
the fact that is called both inside and outside an eval context, and place
it to the caller so that the $ can be escaped when necessary. For symmetry,
move the $(info) statement also out of feature_print_text, and place it to
the caller.

Force the TMP variable evaluation in verbose mode, to display the features
in FEATURE_TESTS that are not in FEATURE_DISPLAY.

Reorder perf feature detection messages (first non-verbose, then verbose
ones) by moving the call to feature_display_entries earlier, before the VF
environment variable check.

Also, remove the newline from that function, as perf might display
additional messages. Move the newline to perf Makefile, and display another
one if displaying the detection result is not deferred as in the case of
bpftool.

Committer testing:

  Collecting the output from:

  $ make VF=1 -C tools/bpf/bpftool/ |& grep "Auto-detecting system features" -A20

  $ diff -u before after
  --- before	2022-08-18 09:59:55.460529231 -0300
  +++ after	2022-08-18 10:01:11.182517282 -0300
  @@ -4,3 +4,5 @@
   ...              libbfd-liberty-z: [ on  ]
   ...                        libcap: [ on  ]
   ...               clang-bpf-co-re: [ on  ]
  +...        disassembler-four-args: [ on  ]
  +...      disassembler-init-styled: [ OFF ]
  $

Fixes: 0afc5cad387db560 ("perf build: Separate feature make support into config/Makefile.feature")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: bpf@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/r/20220818120957.319995-1-roberto.sassu@huaweicloud.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 8 insertions, 11 deletions

diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
index fc6ce0b2535a..9d3afbc37e15 100644
--- a/tools/build/Makefile.feature
+++ b/tools/build/Makefile.feature
@@ -177,7 +177,7 @@ endif
 #
 # Print the result of the feature test:
 #
-feature_print_status = $(eval $(feature_print_status_code)) $(info $(MSG))
+feature_print_status = $(eval $(feature_print_status_code))
 
 define feature_print_status_code
   ifeq ($(feature-$(1)), 1)
@@ -187,7 +187,7 @@ define feature_print_status_code
   endif
 endef
 
-feature_print_text = $(eval $(feature_print_text_code)) $(info $(MSG))
+feature_print_text = $(eval $(feature_print_text_code))
 define feature_print_text_code
     MSG = $(shell printf '...%30s: %s' $(1) $(2))
 endef
@@ -247,21 +247,18 @@ endif
 feature_display_entries = $(eval $(feature_display_entries_code))
 define feature_display_entries_code
   ifeq ($(feature_display),1)
-    $(info )
-    $(info Auto-detecting system features:)
-    $(foreach feat,$(FEATURE_DISPLAY),$(call feature_print_status,$(feat),))
-    ifneq ($(feature_verbose),1)
-      $(info )
-    endif
+    $$(info )
+    $$(info Auto-detecting system features:)
+    $(foreach feat,$(FEATURE_DISPLAY),$(call feature_print_status,$(feat),) $$(info $(MSG)))
   endif
 
   ifeq ($(feature_verbose),1)
-    TMP := $(filter-out $(FEATURE_DISPLAY),$(FEATURE_TESTS))
-    $(foreach feat,$(TMP),$(call feature_print_status,$(feat),))
-    $(info )
+    $(eval TMP := $(filter-out $(FEATURE_DISPLAY),$(FEATURE_TESTS)))
+    $(foreach feat,$(TMP),$(call feature_print_status,$(feat),) $$(info $(MSG)))
   endif
 endef
 
 ifeq ($(FEATURE_DISPLAY_DEFERRED),)
   $(call feature_display_entries)
+  $(info )
 endif