Date:   Sun, 7 Jan 2018 10:31:53 -0800
From:   Martin Kelly <martin@...tingkelly.com>
To:     Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:     kernel-kbuild@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-embedded@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>,
        Matt Mackall <mpm@...enic.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tools: fix cross-compile var export

On 01/07/2018 08:11 AM, Paul Gortmaker wrote:
> [[PATCH] tools: fix cross-compile var export] On 06/01/2018 (Sat 12:16) Martin Kelly wrote:
> 
>> From: Martin Kelly <martin@...tingkelly.com>
>>
>> Currently in a number of Makefiles, we clobber the CC, LD, and/or STRIP env vars
>> when cross-compiling, which breaks any additional flags that might be set (such
>> as sysroot). This easily shows up by using, for instance, a Yocto SDK.
>>
>> Fix this by more carefully overriding the flags in the way that the perf
>> Makefile does.
>>
>> This patch does not fix cross-compile for all the tools (some have other bugs),
>> but it does appear to fix it for these:
>>
>> - cgroup
>> - freefall
>> - gpio
>> - hv
>> - iio
>> - leds
>> - spi
>> - vm
>> - wmi
>>
>> Signed-off-by: Martin Kelly <martin@...tingkelly.com>
>> ---
>> This patch touches multiple subsystems, and there doesn't appear to be a global
>> tools maintainer, so I sent this to linux-embedded kernel-janitors, and
>> linux-kbuild. Please let me know if there is a better place for it.
> 
> I think you will have better luck if you go subsystem by subsystem, e.g.
> send gpio change to gpio maintainer, usb change to usb maintainer and so
> on.  In addition, you'll want to try and understand/explain why those
> lines were added in the 1st place and how it won't break other existing
> use cases by removing them.  Maybe "git blame" will help for that...
> 
> P.
> --
> 

I can send patches subsystem-by-subsystem, but this patch fixes a single 
bug that applies to many Makefiles. It fixes it by putting the correct 
logic into tools/scripts/Makefile.include, which each Makefiles 
includes. If I do this subsystem-by-subsystem, we will just duplicate 
these lines into every Makefile:

+$(call allow-override,CC,$(CROSS_COMPILE)gcc)
+$(call allow-override,AR,$(CROSS_COMPILE)ar)
+$(call allow-override,LD,$(CROSS_COMPILE)ld)
+$(call allow-override,CXX,$(CROSS_COMPILE)g++)
+$(call allow-override,CXX,$(CROSS_COMPILE)strip)

We could do this, but it's a lot of code duplication and means that 
anyone making a new Makefile must also copy the lines or their Makefile 
will have this bug. Since the bug fix generically applies everywhere, I 
think it's most correct for it to go into the common Makefile.

If there is really no maintainer for the tools/scripts/Makefile.include 
file, then maybe I have to send subsystem-by-subsystem, but that seems 
less than ideal.

I do understand why the CC = $(CROSS_COMPILE)gcc lines exist; it is to 
enable cross-compile when you set the $CROSS_COMPILE env var and to use 
native gcc when that is not set. The bug is that if you already have $CC 
set to your cross-compiler (which is what the Yocto SDK and other 
toolchains do), then most of your command-line gets clobbered. Here's an 
example from an ARM Yocto SDK I have:

$ echo $CC
arm-poky-linux-gnueabi-gcc -march=armv7-a -mfpu=neon -mfloat-abi=hard 
-mcpu=cortex-a8 
--sysroot=/home/martin/src/poky/build/sdk/sysroots/cortexa8hf-neon-poky-linux-gnueabi

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

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

Although arm-poky-linux-gnueabi-gcc is a cross-compiler, we've lost many 
build flags, notably --sysroot, which enables us to find the right 
libraries to link against. Without this change, I get this kind of error 
in all the affected Makefiles:

martin@...cade:~/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 unistd.h is in the sysroot, but we've dropped the 
--sysroot flag:
$ find /home/martin/src/poky/build/sdk/sysroots -path 
'*/usr/include/unistd.h'
/home/martin/src/poky/build/sdk/sysroots/cortexa8hf-neon-poky-linux-gnueabi/usr/include/unistd.h

With the change, we add do CC = $(CROSS_COMPILE)gcc if and only if CC is 
not already set. I'm happy to add all these details to the commit 
description.

>>
>>   tools/cgroup/Makefile            |  1 -
>>   tools/gpio/Makefile              |  2 --
>>   tools/hv/Makefile                |  1 -
>>   tools/iio/Makefile               |  2 --
>>   tools/laptop/freefall/Makefile   |  1 -
>>   tools/leds/Makefile              |  1 -
>>   tools/perf/Makefile.perf         |  6 ------
>>   tools/power/acpi/Makefile.config |  3 ---
>>   tools/scripts/Makefile.include   | 18 ++++++++++++++++++
>>   tools/spi/Makefile               |  2 --
>>   tools/usb/Makefile               |  1 -
>>   tools/vm/Makefile                |  1 -
>>   tools/wmi/Makefile               |  1 -
>>   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 31503819454d..68c2d7b059b3 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 68cf1360a3f3..3035ce5f6b36 100644
>> --- a/tools/perf/Makefile.perf
>> +++ b/tools/perf/Makefile.perf
>> @@ -144,12 +144,6 @@ 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 3fab179b1aba..09b2d0f07f66 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,CXX,$(CROSS_COMPILE)strip)
>> +
>>   ifeq ($(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
>>   
>> -- 
>> 2.11.0
>>

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