On Sun, 2018-09-23 at 16:16 +0200, Hauke Mehrtens wrote:
> Hi,
>
> I tried to compile backports against kernel 4.18 and 4.19-rc4 (header
> files from Ubuntu) and ran into this problem when it wants to link the
> kernel:
>
> LD [M]
> /home/hauke/compat-wireless/backports-4.19-rc4-1/drivers/net/wireless/realtek/rtlwifi/rtl_usb.o
> Building modules, stage 2.
> scripts/Makefile.lib:10: *** Recursive variable 'KBUILD_CFLAGS'
> references itself (eventually). Stop.
Hmm. I vaguely remember something like that with our driver, but can't
find it now? I also remember trying to fix it in the upstream kernel ...
Ah yes. This patch:
-subdir-ccflags-y = $(call cc-option,...)
+subdir-ccflags-y := $(call cc-option,...)
My commit log said:
In newer kernels, calling cc-option will use KBUILD_CFLAGS,
which itself gets subdir-ccflags-y added to it. Thus, we get
it referencing itself, since nothing here is evaluated until
KBUILD_CFLAGS is used: KBUILD_CFLAGS contains subdir-ccflags-y,
that in turn contains cc-option call, containing KBUILD_CFLAGS.
To avoid that, use := assignment to subdir-ccflags-y. This
causes make to also evaluate += immediately, cc-option calls
are done right away and we don't end up with KBUILD_CFLAGS
referencing itself.
This fixes build of the driver on kernels 4.15 and higher.
Really in our driver - and it was ChromeOS-specific code too - it was +=
but we had to start with := instead of =.
I don't see something like this in rtlwifi though?
Ah, but we have
subdir-ccflags-y += $(call cc-option, -fno-pie) $(call cc-option, -no-pie)
in backports, so I guess this would help:
--- a/backport/Makefile.kernel
+++ b/backport/Makefile.kernel
@@ -30,7 +30,7 @@ NOSTDINC_FLAGS := \
$(CFLAGS)
endif
-subdir-ccflags-y += $(call cc-option, -fno-pie) $(call cc-option, -no-pie)
+subdir-ccflags-y := $(call cc-option, -fno-pie) $(call cc-option, -no-pie)
ifeq ($(CPTCFG_KERNEL_4_3),y)
subdir-ccflags-y += -Wno-pointer-sign
endif
johannes
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