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SubjectRe: [PATCH 2/3] kbuild: clamp SUBLEVEL to 255
On Mon, Feb 08, 2021 at 01:48:06PM +0000, David Laight wrote:
> From: Sasha Levin
> > Sent: 06 February 2021 03:51
> >
> > Right now if SUBLEVEL becomes larger than 255 it will overflow into the
> > territory of PATCHLEVEL, causing havoc in userspace that tests for
> > specific kernel version.
> >
> > While userspace code tests for MAJOR and PATCHLEVEL, it doesn't test
> > SUBLEVEL at any point as ABI changes don't happen in the context of
> > stable tree.
> >
> > Thus, to avoid overflows, simply clamp SUBLEVEL to it's maximum value in
> > the context of LINUX_VERSION_CODE. This does not affect "make
> > kernelversion" and such.
> >
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> > Makefile | 12 +++++++++---
> > 1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 49ac1b7fe8e99..157be50c691e5 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1258,9 +1258,15 @@ define filechk_utsrelease.h
> > endef
> >
> > define filechk_version.h
> > - echo \#define LINUX_VERSION_CODE $(shell \
> > - expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + 0$(SUBLEVEL)); \
> > - echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))'
> > + if [ $(SUBLEVEL) -gt 255 ]; then \
> > + echo \#define LINUX_VERSION_CODE $(shell \
> > + expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + 255); \
> > + else \
> > + echo \#define LINUX_VERSION_CODE $(shell \
> > + expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + $(SUBLEVEL)); \
> > + fi; \
> > + echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + \
> > + ((c) > 255 ? 255 : (c)))'
> > endef
>
> Why not use KERNEL_VERSION to define LINUX_VERSION_CODE ?
> Basically just:
> echo '#define LINUX_VERSION_CODE KERNEL_VERSION($(VERSION), $(PATCHLEVEL)+0, $(SUBLEVEL)+0)'

Because we are "clamping" LINUX_VERSION_CODE() at a x.y.255, while
KERNEL_VERSION() continues on with the "real" minor number.

thanks,

greg k-h

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