[PATCH] perf build: Improve fix for "argument list too long" error

["Benoît Monin" <benoit.monin@bootlin.com>]

The orphaned pmu-events JSON files are passed to the shell via
`echo "$^"`, which puts the whole list into a single argument. With
a long enough output directory path and enough files, exec'ing
/bin/sh fails with:

  make[5]: /bin/sh: Argument list too long
  make[5]: *** [pmu-events/Build:228: prune_orphans] Error 127

This only happens with out-of-tree builds, when setting O= to a
relatively long path.

To reproduce, build once with JEVENTS_ARCH=all, then rebuild with
a smaller JEVENTS_ARCH without cleaning first, so the leftover files
become orphans. Using nds32 (which leaves ~1100 orphans), an output
path of only ~70 characters is already enough to trigger it:

  OUT=/any/long/path (at least 70 characters)
  make -C tools/perf JEVENTS_ARCH=all   O=$OUT -j$(nproc)
  make -C tools/perf JEVENTS_ARCH=nds32 O=$OUT -j$(nproc)

Express the orphan file list as paths relative to $(OUT_DIR) by
stripping the common prefix and restoring it with printf, the same
approach used in scripts/Makefile.clean, so the shell arguments stay
short.

Fixes: b6712d91f8f5 ("perf build: Prevent "argument list too long" error")
Suggested-by: Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>
Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
Tested-by: Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>
---
 tools/perf/pmu-events/Build | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
index 372773b998e4..4c7b082cb2bb 100644
--- a/tools/perf/pmu-events/Build
+++ b/tools/perf/pmu-events/Build
@@ -223,9 +223,11 @@ ifneq ($(strip $(ORPHAN_FILES)),)
 # of a build step.
 quiet_cmd_rm = RM      ...$(words $^) orphan file(s)...
 
-# The list of files can be long. Use xargs to prevent issues.
+# The list of files can be long. Remove the $(OUT_DIR)/ prefix, and
+# restore it with printf, to prevent "Argument list too long"
+# (see scripts/Makefile.clean).
 prune_orphans: $(ORPHAN_FILES)
-	$(Q)$(call echo-cmd,rm)echo "$^" | xargs rm -f
+	$(Q)$(call echo-cmd,rm)printf '$(OUT_DIR)/%s ' $(patsubst $(OUT_DIR)/%,%,$(ORPHAN_FILES)) | xargs rm -f
 
 JEVENTS_DEPS += prune_orphans
 endif

---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20260925-perf-orphan-args-5e60becd1916

Best regards,
--  
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com