Hi Frank 2018-08-22 3:02 GMT+09:00 Frank Rowand <frowand.list@xxxxxxxxx>: > On 08/21/18 00:18, Masahiro Yamada wrote: >> Hi Frank, >> >> >> 2018-08-21 14:37 GMT+09:00 Frank Rowand <frowand.list@xxxxxxxxx>: >>> On 08/20/18 19:08, Masahiro Yamada wrote: >>>> Hi Frank, >>>> >>>> 2018-08-21 10:31 GMT+09:00 Frank Rowand <frowand.list@xxxxxxxxx>: >>>>> On 08/20/18 14:32, Rob Herring wrote: >>>>>> On Mon, Aug 20, 2018 at 1:55 PM Frank Rowand <frowand.list@xxxxxxxxx> wrote: >>>>>>> >>>>>>> On 07/03/18 18:59, Masahiro Yamada wrote: >>>>>>>> It is tedious to specify extra compiler options for every file. >>>>>>>> HOST_EXTRACFLAGS is useful to add options to all files in a >>>>>>>> directory. >>>>>>>> >>>>>>>> -I$(src)/libfdt is needed for all the files in this directory >>>>>>>> to include libfdt_env.h etc. from scripts/dtc/libfdt/. >>>>>>>> >>>>>>>> On the other hand, -I$(src) is used to include check-in headers >>>>>>>> from generated C files. Thus, I added it only to dtc-lexer.lex.o >>>>>>>> and dtc-parser.tab.o . >>>>>>>> >>>>>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> >>>>>>>> --- >>>>>>>> >>>>>>>> scripts/dtc/Makefile | 18 ++++-------------- >>>>>>>> 1 file changed, 4 insertions(+), 14 deletions(-) >>>>>>>> >>>>>>>> diff --git a/scripts/dtc/Makefile b/scripts/dtc/Makefile >>>>>>>> index 9cac65b..1c943e0 100644 >>>>>>>> --- a/scripts/dtc/Makefile >>>>>>>> +++ b/scripts/dtc/Makefile >>>>>>>> @@ -9,21 +9,11 @@ dtc-objs := dtc.o flattree.o fstree.o data.o livetree.o treesource.o \ >>>>>>>> dtc-objs += dtc-lexer.lex.o dtc-parser.tab.o >>>>>>>> >>>>>>>> # Source files need to get at the userspace version of libfdt_env.h to compile >>>>>>>> +HOST_EXTRACFLAGS := -I$(src)/libfdt >>>>>>> >>>>>>> Shouldn't that be += instead of :=? >>>>>> >>>>>> I don't think so. The definition is local to the file (and reset >>>>>> before each makefile is included). >>>>>> >>>>>> Rob >>>>>> >>>>> >>>>> Every other place where HOST_EXTRACFLAGS is assigned a value, += is used >>>>> instead of :=, including the example in Documentation/kbuild/makefiles.txt >>>>> >>>>> What makes scripts/dtc/Makefile different than the other makefiles? >>>>> >>>>> -Frank >>>>> >>>> >>>> >>>> := and += work in the same way in here. >>> >>> Unless I do: HOST_EXTRACFLAGS=xxx make >>> where "xxx" is some random flag I feel like adding in a particular build. >> >> >> >> This is not the intended usage of HOST_EXTRACFLAGS. > > I seem to have found a useful feature for making a specific object in a > development context with additional compiler flags. But a feature that > you say is not intended. > > I do understand that there is an intended difference between HOSTCFLAGS > and HOST_EXTRACFLAGS. But I do not agree that using HOST_EXTRACFLAGS > on the make commandline when building a single object in a development > context is abuse. > > >> HOST_EXTRACFLAGS is supposed to be set by Makefile in the kernel tree. > > But it is not set, thus it is currently available (and has been for many > years) for the usage that I specified above. Right. People often find something that happens to work. HOST_EXTRACFLAGS=xxx make works, but make HOST_EXTRACFLAGS=xxx does not because it really overrides += in makefiles. > >> Documentation/kbuild/makefiles.txt explains this: >> >> To set flags that will take effect for all host programs created >> in that Makefile, use the variable HOST_EXTRACFLAGS. >> >> >> >> If you want to pass additional host compiler flags, >> please use HOSTCFLAGS instead. > > That will not work because the top level Makefile has: > > HOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \ > > >> Documentation/kbuild/kbuild.txt lists officially supported >> environment variables / command line variables.> >> HOSTCFLAGS >> -------------------------------------------------- >> Additional flags to be passed to $(HOSTCC) when building host programs. > > HOSTCFLAGS is not in my 4.18.0 Documentation/kbuild/kbuild.txt. What version are > you looking at? > > $ git log -n1 > commit 94710cac0ef4ee177a63b5227664b38c95bbf703 > Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Date: Sun Aug 12 13:41:04 2018 -0700 > > Linux 4.18 > $ git grep HOSTCFLAGS Documentation/kbuild/kbuild.txt > $ Please check the latest Linus tree. Commit f92d19e0ef9bbbb2984845682e740934ad45473b was merged in this MW. > > But this is where I concede that HOST_EXTRACFLAGS is also not listed as > an officially supported environment variable or command line variable. I > had not checked here for that limitation. > > >> >> >> Maybe I should add >> >> HOST_EXTRACFLAGS := >> HOST_EXTRACXXFLAGS := >> >> to the top of scripts/Makefile.build >> to reset the variables explicitly >> in case people try to abuse them. > > Yes, if you intend that it not be possible to initialize them in the make > command then you should initialize them. If you do that, it is easy > enough for me to patch the initialization out in cases where I want the > extra functionality. -- Best Regards Masahiro Yamada
