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SubjectRe: 4.17.x won't boot due to "x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G"
On Sat, Jul 07, 2018 at 10:21:47AM +0900, Masahiro Yamada wrote:
> 2018-07-07 1:29 GMT+09:00 Kirill A. Shutemov <kirill@shutemov.name>:
> > On Fri, Jul 06, 2018 at 11:13:02PM +0900, Masahiro Yamada wrote:
> >> >> LDFLAGS is for internal-use.
> >> >> Please do not override it from the command line.
> >> >
> >> > Can we generate a build error if a user try to override LDFLAGS, CFLAGS or
> >> > other critical internal-use-only variables?
> >>
> >> Yes, Make can check where variables came from.
> >
> > I think we should do this.
> >
> >> >> make LDFLAGS_KERNEL=... LDFLAGS_MODULE=...
> >> >> will allow you to append linker flags.
> >> >
> >> > Okay. It makes me wounder if we should taint kernel in such cases?
> >> > Custom compiler/linker flags are risky and can lead to weird bugs.
> >>
> >> OK.
> >> So, what problem are we discussing?
> >
> > Users set custom LDFLAGS/CFLAGS and break kernel. Then report bug that
> > hard to debug. See
> >
> > https://bugzilla.kernel.org/show_bug.cgi?id=200385
>
>
> CFLAGS is only used under tools/.
> Passing CFLAGS is probably no effect to the kernel.
>
> In Linux makefiles,
> KBUILD_ prefixed variables are used internally.
>
> KBUILD_CFLAGS, KBUILD_CPPFLAGS, KBUILD_AFLAGS, etc.
>
>
> LDFLAGS is an exception. I do not know why.
> Renaming LDFLAGS to KBUILD_LDFLAGS
> will make the code consistent.
>
> At least, it will avoid overriding flags by accident.
>
> Of course, users still can change KBUILD_LDFLAGS
> if they really want.
>
> The build system could add belt and braces checks for that,
> but it is arguable since
> there are lots of lots of internal variables.

I think renaming LDFLAGS to KBUILD_LDFLAGS is good idea.
Would you prepare patch?

--
Kirill A. Shutemov

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