Re: [LTP] [RFC] HOST_{CFLAGS,LDFLAGS} definition

[Joerg Vehlow <lkml@jv-coder.de>]

Hi Petr,
sorry for the resend, forgot the mailing list

Am 1/27/2022 um 11:57 AM schrieb Petr Vorel:
> Hi,
> 
> not sure what I do wrong, but due evaluation in include/mk/config.mk.in:
> 
> ifeq ($(strip $(HOST_CFLAGS)),)
> HOST_CFLAGS := $(CFLAGS)
> endif
> 
> ifeq ($(strip $(HOST_LDFLAGS)),)
> HOST_LDFLAGS := $(LDFLAGS)
> endif
> 
> HOST_CFLAGS and HOST_LDFLAGS must be defined for make (not for configure).
> Of course exporting variables works.
> 
> Also whole point of previous code was to have a default, but that's wrong.
> On some embedded platforms it fails as without properly defined HOST_CFLAGS it
> can inherit flags which aren't usable for host (e.g. -mlongcalls
> -mauto-litpools) and whole compilation fails.

Having the default is required for native builds.
The only problem I see with this is that empty HOST_CFLAGS passed
through the environment is not possible using the current
implementation. It is however possible passing en empte HOST_CFLAGS as
make parameter:

Makefile:
CFLAGS := cflags

ifeq ($(strip $(HOST_CFLAGS)),)
HOST_CFLAGS := $(CFLAGS)
endif

all:
	@echo "Value of HOST_CFLAGS: '${HOST_CFLAGS}'"


$ make
Value of HOST_CFLAGS: 'cflags'

$ make HOST_CFLAGS=host
Value of HOST_CFLAGS: 'host'

$ make HOST_CFLAGS=
Value of HOST_CFLAGS: ''


> IMHO we should change it to (i.e. not inherit anything):
> 
> HOST_CFLAGS := $(HOST_CFLAGS)
> HOST_LDFLAGS := $(HOST_LDFLAGS)
> 
> HOST_CFLAGS += $(WLDFLAGS)
> HOST_LDFLAGS += $(DEBUG_CFLAGS) $(OPT_CFLAGS) $(WCFLAGS)
> 
This wouldn't have any effect if HOST_CFLAGS is passed as parameter to
make and would be even worse than the current solution, if HOST_CFLAGS
is passed on the shell. You do not want any default switches, that are
not absolutely necessary, otherwise you can have the same problem as
before: Incompatibility with the host compiler.

Maybe we should learn from the kernel here. It doesn't have a
HOST_CFLAGS, just a HOSTCC. If you want to add CFLAGS for the host, you
just append it to the HOSTCC.

Joerg

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