perf build: Fix out of tree build related to installation of sysreg-defs

[ Upstream commit efae55b ]

It seems that a previous modification to sysreg-defs, which corrected
emitting the header to the specified output directory, exposed missing
subdir, prefix variables.

This breaks out of tree builds of perf as the file is now built into the
output directory, but still tries to descend into output directory as a
subdir.

Fixes: a29ee6a ("perf build: Ensure sysreg-defs Makefile respects output dir")
Reviewed-by: Oliver Upton <[email protected]>
Reviewed-by: Tycho Andersen <[email protected]>
Signed-off-by: Ethan Adams <[email protected]>
Tested-by: Tycho Andersen <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

tools/perf/Makefile.perf

@@ -458,18 +458,19 @@ SHELL = $(SHELL_PATH)
 
 arm64_gen_sysreg_dir := $(srctree)/tools/arch/arm64/tools
 ifneq ($(OUTPUT),)
-  arm64_gen_sysreg_outdir := $(OUTPUT)
+  arm64_gen_sysreg_outdir := $(abspath $(OUTPUT))
 else
   arm64_gen_sysreg_outdir := $(CURDIR)
 endif
 
 arm64-sysreg-defs: FORCE
-	$(Q)$(MAKE) -C $(arm64_gen_sysreg_dir) O=$(arm64_gen_sysreg_outdir)
+	$(Q)$(MAKE) -C $(arm64_gen_sysreg_dir) O=$(arm64_gen_sysreg_outdir) \
+		prefix= subdir=
 
 arm64-sysreg-defs-clean:
 	$(call QUIET_CLEAN,arm64-sysreg-defs)
 	$(Q)$(MAKE) -C $(arm64_gen_sysreg_dir) O=$(arm64_gen_sysreg_outdir) \
-		clean > /dev/null
+		prefix= subdir= clean > /dev/null
 
 beauty_linux_dir := $(srctree)/tools/perf/trace/beauty/include/linux/
 linux_uapi_dir := $(srctree)/tools/include/uapi/linux