tools/perf/build: Fix O=/some/dir perf.o type of targets

If someone specifies a single target, mixed with O=, the following way:

    hubble:~/tip/tools/perf> make O=/tmp/perf util/stat.o
    BUILD: Doing 'make -j8' parallel build
    gcc  -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security -Wformat-y2k [...]

The build might even fail, if a target depends on other targets:

    hubble:~/tip/tools/perf> make O=/tmp/perf perf.o
    ...
    perf.c: In function ‘handle_options’:
    perf.c:155:21: error: ‘PERF_HTML_PATH’ undeclared (first use in this function)

The correct way to invoke such targets is:

    hubble:~/tip/tools/perf> make O=/tmp/perf /tmp/perf/perf.o
    BUILD: Doing 'make -j8' parallel build
    GEN /tmp/perf/common-cmds.h
    CC /tmp/perf/perf.o

But that's unnecessary typing and it's also easy to mistakenly build into the
source directory.

To fix this remove the generic suffix rules and add redirection to $(OUTPUT)
for the most popular .o targets.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-mk0oiukmhgSbrll6chrPkkqr@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 178a1c87db13..a24f6c280b95 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -576,7 +576,21 @@ $(OUTPUT)perf.o perf.spec \
         : $(OUTPUT)PERF-VERSION-FILE
 
 .SUFFIXES:
-.SUFFIXES: .o .c .S .s
+
+#
+# If a target does not match any of the later rules then prefix it by $(OUTPUT)
+# This makes targets like 'make O=/tmp/perf perf.o' work in a natural way.
+#
+ifneq ($(OUTPUT),)
+%.o: $(OUTPUT)%.o
+        @echo "    # Redirected target $@ => $(OUTPUT)$@"
+util/%.o: $(OUTPUT)util/%.o
+        @echo "    # Redirected target $@ => $(OUTPUT)util/$@"
+bench/%.o: $(OUTPUT)bench/%.o
+        @echo "    # Redirected target $@ => $(OUTPUT)bench/$@"
+tests/%.o: $(OUTPUT)tests/%.o
+        @echo "    # Redirected target $@ => $(OUTPUT)tests/$@"
+endif
 
 # These two need to be here so that when O= is not used they take precedence
 # over the general rule for .o