Re: Makefile: CC_IMPLICIT_FALLTHROUGH passed quoted as argument to gcc

[Salvatore Bonaccorso]

Hi,

On Mon, Dec 06, 2021 at 11:53:41AM -0800, Kees Cook wrote:
> On Sun, Dec 05, 2021 at 02:54:05AM +0900, Masahiro Yamada wrote:
> > On Sun, Dec 5, 2021 at 1:53 AM Linus Torvalds
> > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Sat, Dec 4, 2021 at 5:13 AM Salvatore Bonaccorso <carnil@xxxxxxxxxx> wrote:
> > > >
> > > > Andreas suggested to replace the
> > > >
> > > > KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
> > > >
> > > > with
> > > >
> > > > KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(patsubst "%",%,$(CONFIG_CC_IMPLICIT_FALLTHROUGH))
> > >
> > > Ugh. I think the external build environment is a bit broken, but
> > > whatever. The above is ugly but I guess it works.
> > >
> > > Another alternative would be to make the Kconfig strings simply not
> > > have '"' as part of them.
> > >
> > > When you do
> > >
> > >     a = "hello"
> > >     print $a
> > >
> > > in any normal language, you generally wouldn't expect it to print the
> > > quotes, it should just print the bare word.
> > >
> > > But that's what the Kconfig string language basically does in this
> > > case. And I guess several users expect and take advantage of that ;(
> > >
> > > Masahiro? Comments?
> > 
> > Yes, you get to the point.
> > 
> > In fact, this is in my TODO list for a while
> > (and this is the reason I was doing prerequisite Kconfig refactoring
> > in the previous development cycle).
> > I will try to find some spare time to complete this work.
> > 
> > 
> > 
> > Kconfig generates two similar files,
> > 
> >  -   .config
> >  -   include/config/auto.conf
> > 
> > Changing the format of the .config is presumably problematic
> > since it is the saved user configuration as well.
> > 
> > It is possible (and more reasonable) to change include/config/auto.conf
> > so strings are not quoted.
> > 
> > In Makefiles, quotations are just normal characters; they have no
> > special functionality.
> > 
> > So, in Makefile context, it is more handy to do
> > 
> >      CONFIG_X=foo bar
> > 
> > instead of
> > 
> >     CONFIG_X="foo bar"
> > 
> > 
> > 
> > One problem is include/config/auto.conf is included not only by Makefiles
> > but also by shell scripts.
> > 
> > 
> > In shell context, the right hand side must be quoted
> > in case the value contains spaces.
> > 
> >    CONFIG_X="foo bar"
> > 
> > 
> > 
> > My plan is to fix
> >   scripts/link-vmlinux.sh
> >   scripts/gen_autoksyms.sh
> > etc. to not directly include the auto.conf.
> > Later, change Kconfig to generate the auto.conf without "".
> > 
> > 
> > 
> > In the meantime,
> > 
> > KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(patsubst
> > "%",%,$(CONFIG_CC_IMPLICIT_FALLTHROUGH))
> > 
> >  or if you prefer slightly shorter form,
> > 
> > KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH:"%"=%)
> > 
> > will be a workaround.
> 
> It'll be nice to get this fixed. There are a few places where there is
> a test for a compiler flag in Kconfig, and then the option is repeated
> in the Makefile, due to the above quoting issues. For example:
> 
> arch/arm64/Kconfig:
> 	config CC_HAS_BRANCH_PROT_PAC_RET
> 	     # GCC 9 or later, clang 8 or later
> 	     def_bool $(cc-option,-mbranch-protection=pac-ret+leaf)
> 
> arch/arm64/Makefile:
> 	branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
> 
> 
> I like the $(CONFIG_CC_IMPLICIT_FALLTHROUGH:"%"=%) solution: it's short.

Does the following look correct, as well from formal style/commit
description? I have not yet done many contributions directly.

Regards,
Salvatore