[PATCH] trace-cmd: Allow building with GNU Make 4.4

[Michal Sojka <michal.sojka@xxxxxxx>]

Make 4.4 introduces several backward incompatibilities and the result
is that building trace-cmd with it never finishes. It seems that make
ends up in some kind of infinite recursion. The symptoms are:

    $ make -d
    GNU Make 4.4
    Built for x86_64-pc-linux-gnu
    Copyright (C) 1988-2022 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.
    Reading makefiles...
    Reading makefile 'Makefile'...
    Makefile:79: not recursively expanding pkgconfig_dir to export to shell function
    Makefile:79: not recursively expanding pkgconfig_dir to export to shell function
    Makefile:224: not recursively expanding LIBTRACECMD_SHARED_VERSION to export to shell function
    Makefile:79: not recursively expanding pkgconfig_dir to export to shell function
    Makefile:224: not recursively expanding LIBTRACECMD_SHARED_VERSION to export to shell function
    Makefile:225: not recursively expanding LIBTRACECMD_SHARED_SO to export to shell function
    Makefile:79: not recursively expanding pkgconfig_dir to export to shell function
    Makefile:79: not recursively expanding pkgconfig_dir to export to shell function

Build succeeds if recursively expanded variables (defined with '='),
which use $(shell ...) as its value, are replaced with simply expanded
variables (defined with ':=').

Signed-off-by: Michal Sojka <michal.sojka@xxxxxxx>
---
 Makefile | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/Makefile b/Makefile
index bda49dd..d50e625 100644
--- a/Makefile
+++ b/Makefile
@@ -221,8 +221,8 @@ LIBS ?= -ldl
 LIBTRACECMD_DIR = $(obj)/lib/trace-cmd
 LIBTRACECMD_STATIC = $(LIBTRACECMD_DIR)/libtracecmd.a
 LIBTRACECMD_SHARED = $(LIBTRACECMD_DIR)/libtracecmd.so.$(LIBTRACECMD_VERSION)
-LIBTRACECMD_SHARED_VERSION = $(shell echo $(LIBTRACECMD_SHARED) | sed -e 's/\(\.so\.[0-9]*\).*/\1/')
-LIBTRACECMD_SHARED_SO = $(shell echo $(LIBTRACECMD_SHARED) | sed -e 's/\(\.so\).*/\1/')
+LIBTRACECMD_SHARED_VERSION := $(shell echo $(LIBTRACECMD_SHARED) | sed -e 's/\(\.so\.[0-9]*\).*/\1/')
+LIBTRACECMD_SHARED_SO := $(shell echo $(LIBTRACECMD_SHARED) | sed -e 's/\(\.so\).*/\1/')
 
 export LIBTRACECMD_STATIC LIBTRACECMD_SHARED
 export LIBTRACECMD_SHARED_VERSION LIBTRACECMD_SHARED_SO
@@ -230,12 +230,12 @@ export LIBTRACECMD_SHARED_VERSION LIBTRACECMD_SHARED_SO
 LIBTRACEEVENT=libtraceevent
 LIBTRACEFS=libtracefs
 
-TEST_LIBTRACEEVENT = $(shell sh -c "$(PKG_CONFIG) --atleast-version $(LIBTRACEEVENT_MIN_VERSION) $(LIBTRACEEVENT) > /dev/null 2>&1 && echo y")
-TEST_LIBTRACEFS = $(shell sh -c "$(PKG_CONFIG) --atleast-version $(LIBTRACEFS_MIN_VERSION) $(LIBTRACEFS) > /dev/null 2>&1 && echo y")
+TEST_LIBTRACEEVENT := $(shell sh -c "$(PKG_CONFIG) --atleast-version $(LIBTRACEEVENT_MIN_VERSION) $(LIBTRACEEVENT) > /dev/null 2>&1 && echo y")
+TEST_LIBTRACEFS := $(shell sh -c "$(PKG_CONFIG) --atleast-version $(LIBTRACEFS_MIN_VERSION) $(LIBTRACEFS) > /dev/null 2>&1 && echo y")
 
 ifeq ("$(TEST_LIBTRACEEVENT)", "y")
-LIBTRACEEVENT_CFLAGS = $(shell sh -c "$(PKG_CONFIG) --cflags $(LIBTRACEEVENT)")
-LIBTRACEEVENT_LDLAGS = $(shell sh -c "$(PKG_CONFIG) --libs $(LIBTRACEEVENT)")
+LIBTRACEEVENT_CFLAGS := $(shell sh -c "$(PKG_CONFIG) --cflags $(LIBTRACEEVENT)")
+LIBTRACEEVENT_LDLAGS := $(shell sh -c "$(PKG_CONFIG) --libs $(LIBTRACEEVENT)")
 else
 .PHONY: warning
 warning:
@@ -253,8 +253,8 @@ endif
 export LIBTRACEEVENT_CFLAGS LIBTRACEEVENT_LDLAGS
 
 ifeq ("$(TEST_LIBTRACEFS)", "y")
-LIBTRACEFS_CFLAGS = $(shell sh -c "$(PKG_CONFIG) --cflags $(LIBTRACEFS)")
-LIBTRACEFS_LDLAGS = $(shell sh -c "$(PKG_CONFIG) --libs $(LIBTRACEFS)")
+LIBTRACEFS_CFLAGS := $(shell sh -c "$(PKG_CONFIG) --cflags $(LIBTRACEFS)")
+LIBTRACEFS_LDLAGS := $(shell sh -c "$(PKG_CONFIG) --libs $(LIBTRACEFS)")
 else
 .PHONY: warning
 warning:
@@ -324,11 +324,11 @@ endif
 export ZLIB_LDLAGS
 
 ifndef NO_LIBZSTD
-TEST_LIBZSTD = $(shell sh -c "$(PKG_CONFIG) --atleast-version 1.4.0 libzstd > /dev/null 2>&1 && echo y")
+TEST_LIBZSTD := $(shell sh -c "$(PKG_CONFIG) --atleast-version 1.4.0 libzstd > /dev/null 2>&1 && echo y")
 
 ifeq ("$(TEST_LIBZSTD)", "y")
-LIBZSTD_CFLAGS = $(shell sh -c "$(PKG_CONFIG) --cflags libzstd")
-LIBZSTD_LDLAGS = $(shell sh -c "$(PKG_CONFIG) --libs libzstd")
+LIBZSTD_CFLAGS := $(shell sh -c "$(PKG_CONFIG) --cflags libzstd")
+LIBZSTD_LDLAGS := $(shell sh -c "$(PKG_CONFIG) --libs libzstd")
 CFLAGS += -DHAVE_ZSTD
 ZSTD_INSTALLED=1
 $(info    Have ZSTD compression support)
-- 
2.38.1