tools: fix cross-compile var clobbering

Currently a number of Makefiles break when used with toolchains that
pass extra flags in CC and other cross-compile related variables (such
as --sysroot).

Thus we get this error when we use a toolchain that puts --sysroot in
the CC var:

  ~/src/linux/tools$ make iio
  [snip]
  iio_event_monitor.c:18:10: fatal error: unistd.h: No such file or directory
    #include <unistd.h>
             ^~~~~~~~~~

This occurs because we clobber several env vars related to
cross-compiling with lines like this:

  CC = $(CROSS_COMPILE)gcc

Although this will point to a valid cross-compiler, we lose any extra
flags that might exist in the CC variable, which can break toolchains
that rely on them (for example, those that use --sysroot).

This easily shows up using a Yocto SDK:

  $ . [snip]/sdk/environment-setup-cortexa8hf-neon-poky-linux-gnueabi

  $ echo $CC
  arm-poky-linux-gnueabi-gcc -march=armv7-a -mfpu=neon -mfloat-abi=hard
  -mcpu=cortex-a8
  --sysroot=[snip]/sdk/sysroots/cortexa8hf-neon-poky-linux-gnueabi

  $ echo $CROSS_COMPILE
  arm-poky-linux-gnueabi-

  $ echo ${CROSS_COMPILE}gcc
  krm-poky-linux-gnueabi-gcc

Although arm-poky-linux-gnueabi-gcc is a cross-compiler, we've lost the
--sysroot and other flags that enable us to find the right libraries to
link against, so we can't find unistd.h and other libraries and headers.
Normally with the --sysroot flag we would find unistd.h in the sdk
directory in the sysroot:

  $ find [snip]/sdk/sysroots -path '*/usr/include/unistd.h'
  [snip]/sdk/sysroots/cortexa8hf-neon-poky-linux-gnueabi/usr/include/unistd.h

The perf Makefile adds CC = $(CROSS_COMPILE)gcc if and only if CC is not
already set, and it compiles correctly with the above toolchain.

So, generalize the logic that perf uses in the common Makefile and
remove the manual CC = $(CROSS_COMPILE)gcc lines from each Makefile.

Note that this patch does not fix cross-compile for all the tools (some
have other bugs), but it does fix it for all except usb and acpi, which
still have other unrelated issues.

I tested both with and without the patch on native and cross-build and
there appear to be no regressions.

Link: http://lkml.kernel.org/r/20180107214028.23771-1-martin@martingkelly.com
Signed-off-by: Martin Kelly <martin@martingkelly.com>
Acked-by: Mark Brown <broonie@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Pali Rohar <pali.rohar@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Robert Moore <robert.moore@intel.com>
Cc: Lv Zheng <lv.zheng@intel.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Valentina Manea <valentina.manea.m@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

13 files changed, 18 insertions, 22 deletions

diff --git a/tools/cgroup/Makefile b/tools/cgroup/Makefile
index 860fa151640a..ffca068e4a76 100644
--- a/tools/cgroup/Makefile
+++ b/tools/cgroup/Makefile
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 # Makefile for cgroup tools
 
-CC = $(CROSS_COMPILE)gcc
 CFLAGS = -Wall -Wextra
 
 all: cgroup_event_listener
diff --git a/tools/gpio/Makefile b/tools/gpio/Makefile
index 805a2c0cf4cd..240eda014b37 100644
--- a/tools/gpio/Makefile
+++ b/tools/gpio/Makefile
@@ -12,8 +12,6 @@ endif
 # (this improves performance and avoids hard-to-debug behaviour);
 MAKEFLAGS += -r
 
-CC = $(CROSS_COMPILE)gcc
-LD = $(CROSS_COMPILE)ld
 CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
 
 ALL_TARGETS := lsgpio gpio-hammer gpio-event-mon
diff --git a/tools/hv/Makefile b/tools/hv/Makefile
index 1139d71fa0cf..5db5e62cebda 100644
--- a/tools/hv/Makefile
+++ b/tools/hv/Makefile
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 # Makefile for Hyper-V tools
 
-CC = $(CROSS_COMPILE)gcc
 WARNINGS = -Wall -Wextra
 CFLAGS = $(WARNINGS) -g $(shell getconf LFS_CFLAGS)
 
diff --git a/tools/iio/Makefile b/tools/iio/Makefile
index a08e7a47d6a3..332ed2f6c2c2 100644
--- a/tools/iio/Makefile
+++ b/tools/iio/Makefile
@@ -12,8 +12,6 @@ endif
 # (this improves performance and avoids hard-to-debug behaviour);
 MAKEFLAGS += -r
 
-CC = $(CROSS_COMPILE)gcc
-LD = $(CROSS_COMPILE)ld
 CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
 
 ALL_TARGETS := iio_event_monitor lsiio iio_generic_buffer
diff --git a/tools/laptop/freefall/Makefile b/tools/laptop/freefall/Makefile
index 5f758c489a20..b572d94255f6 100644
--- a/tools/laptop/freefall/Makefile
+++ b/tools/laptop/freefall/Makefile
@@ -2,7 +2,6 @@
 PREFIX ?= /usr
 SBINDIR ?= sbin
 INSTALL ?= install
-CC = $(CROSS_COMPILE)gcc
 
 TARGET = freefall
 
diff --git a/tools/leds/Makefile b/tools/leds/Makefile
index c379af003807..7b6bed13daaa 100644
--- a/tools/leds/Makefile
+++ b/tools/leds/Makefile
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 # Makefile for LEDs tools
 
-CC = $(CROSS_COMPILE)gcc
 CFLAGS = -Wall -Wextra -g -I../../include/uapi
 
 all: uledmon led_hw_brightness_mon
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 9b0351d3ce34..012328038594 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -146,12 +146,6 @@ define allow-override
     $(eval $(1) = $(2)))
 endef
 
-# Allow setting CC and AR and LD, or setting CROSS_COMPILE as a prefix.
-$(call allow-override,CC,$(CROSS_COMPILE)gcc)
-$(call allow-override,AR,$(CROSS_COMPILE)ar)
-$(call allow-override,LD,$(CROSS_COMPILE)ld)
-$(call allow-override,CXX,$(CROSS_COMPILE)g++)
-
 LD += $(EXTRA_LDFLAGS)
 
 HOSTCC  ?= gcc
diff --git a/tools/power/acpi/Makefile.config b/tools/power/acpi/Makefile.config
index a1883bbb0144..2cccbba64418 100644
--- a/tools/power/acpi/Makefile.config
+++ b/tools/power/acpi/Makefile.config
@@ -56,9 +56,6 @@ INSTALL_SCRIPT = ${INSTALL_PROGRAM}
 # to compile vs uClibc, that can be done here as well.
 CROSS = #/usr/i386-linux-uclibc/usr/bin/i386-uclibc-
 CROSS_COMPILE ?= $(CROSS)
-CC = $(CROSS_COMPILE)gcc
-LD = $(CROSS_COMPILE)gcc
-STRIP = $(CROSS_COMPILE)strip
 HOSTCC = gcc
 
 # check if compiler option is supported
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index fcb3ed0be5f8..dd614463d4d6 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -42,6 +42,24 @@ EXTRA_WARNINGS += -Wformat
 
 CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)
 
+# Makefiles suck: This macro sets a default value of $(2) for the
+# variable named by $(1), unless the variable has been set by
+# environment or command line. This is necessary for CC and AR
+# because make sets default values, so the simpler ?= approach
+# won't work as expected.
+define allow-override
+  $(if $(or $(findstring environment,$(origin $(1))),\
+            $(findstring command line,$(origin $(1)))),,\
+    $(eval $(1) = $(2)))
+endef
+
+# Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
+$(call allow-override,CC,$(CROSS_COMPILE)gcc)
+$(call allow-override,AR,$(CROSS_COMPILE)ar)
+$(call allow-override,LD,$(CROSS_COMPILE)ld)
+$(call allow-override,CXX,$(CROSS_COMPILE)g++)
+$(call allow-override,STRIP,$(CROSS_COMPILE)strip)
+
 ifeq ($(CC_NO_CLANG), 1)
 EXTRA_WARNINGS += -Wstrict-aliasing=3
 endif
diff --git a/tools/spi/Makefile b/tools/spi/Makefile
index 90615e10c79a..815d15589177 100644
--- a/tools/spi/Makefile
+++ b/tools/spi/Makefile
@@ -11,8 +11,6 @@ endif
 # (this improves performance and avoids hard-to-debug behaviour);
 MAKEFLAGS += -r
 
-CC = $(CROSS_COMPILE)gcc
-LD = $(CROSS_COMPILE)ld
 CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
 
 ALL_TARGETS := spidev_test spidev_fdx
diff --git a/tools/usb/Makefile b/tools/usb/Makefile
index 4e6506078494..01d758d73b6d 100644
--- a/tools/usb/Makefile
+++ b/tools/usb/Makefile
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 # Makefile for USB tools
 
-CC = $(CROSS_COMPILE)gcc
 PTHREAD_LIBS = -lpthread
 WARNINGS = -Wall -Wextra
 CFLAGS = $(WARNINGS) -g -I../include
diff --git a/tools/vm/Makefile b/tools/vm/Makefile
index be320b905ea7..20f6cf04377f 100644
--- a/tools/vm/Makefile
+++ b/tools/vm/Makefile
@@ -6,7 +6,6 @@ TARGETS=page-types slabinfo page_owner_sort
 LIB_DIR = ../lib/api
 LIBS = $(LIB_DIR)/libapi.a
 
-CC = $(CROSS_COMPILE)gcc
 CFLAGS = -Wall -Wextra -I../lib/
 LDFLAGS = $(LIBS)
 
diff --git a/tools/wmi/Makefile b/tools/wmi/Makefile
index e664f1167388..e0e87239126b 100644
--- a/tools/wmi/Makefile
+++ b/tools/wmi/Makefile
@@ -2,7 +2,6 @@ PREFIX ?= /usr
 SBINDIR ?= sbin
 INSTALL ?= install
 CFLAGS += -D__EXPORTED_HEADERS__ -I../../include/uapi -I../../include
-CC = $(CROSS_COMPILE)gcc
 
 TARGET = dell-smbios-example