Re: s390/nospec: add an option to use thunk-extern

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Hi Joe,

c4e789572557 ("s390/nospec: build expoline.o for modules_prepare target") is now in linux.git.

Note: arch/s390/lib/expoline.o is moved to arch/s390/lib/expoline/expoline.o. This means kernel-devel package in fedora should also include this updated file path.

Thanks

On 7/1/22 23:39, Joe Lawrence wrote:
On 7/1/22 5:18 PM, C. Erastus Toe wrote:
On Wed, Jun 29, 2022 at 11:16 AM Joe Lawrence <joe.lawrence@xxxxxxxxxx
<mailto:joe.lawrence@xxxxxxxxxx>> wrote:

     On 6/27/22 8:50 AM, Vasily Gorbik wrote:
     > Hi Joe,
     >
     > sorry for late reply.
     >
     >> I couldn't find the upstream patch post for 1d2ad084800e
     ("s390/nospec:
     >> add an option to use thunk-extern"), so replying off-list here.  Feel
     >> free to cc the appropriate list.
     >>
     >> Regarding this change, as I understand it, when
     CONFIG_EXPOLINE_EXTERN=y
     >> out-of-tree kernel modules will need to link against
     >> arch/s390x/lib/expoline.o, right?
     >>
     >> And if so, shouldn't the top level 'prepare_modules' target create
     >> expoline.o for this purpose?
     >
     > Thanks for bringing this up. I definitely missed out-of-tree
     kernel modules
     > build case without a prebuilt kernel. On the other hand this
     post-linking
     > trick is a rip off from powerpc:
     >
     > KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
     >
     > So, now I wonder why powerpc doesn't have crtsavres.o in
     'prepare_modules'.
     >
     > Anyhow, below is couple of patches to consider. The first one is
     > meant to be backportable, as the second one requires 4efd417f298b.
     >
     > I had to move expoline.S to a separate directory to be able to
     call into
     > its Makefile for 'prepare_modules' and avoid warnings for other
     targets
     > defined in the same Makefile. Not sure if there are better kbuild
     tricks
     > I could use. Another option I thought about is to keep expoline.S
     where
     > it is and add a condition into that Makefile:
     > expoline_prepare: prepare0
     >       $(Q)$(MAKE) $(build)=arch/s390/lib expoline_prepare=1
     arch/s390/lib/expoline.o
     >
     > arch/s390/lib/Makefile:
     > # first target defined
     > obj-$(CONFIG_EXPOLINE_EXTERN) += expoline.o
     > ifndef expoline_prepare
     > # ...other targets...
     >
     > Vasily Gorbik (2):
     >   s390/nospec: build expoline.o for modules_prepare target
     >   s390/nospec: remove unneeded header includes
     >
     >  arch/s390/Makefile                      | 8 +++++++-
     >  arch/s390/include/asm/nospec-insn.h     | 2 --
     >  arch/s390/lib/Makefile                  | 3 ++-
     >  arch/s390/lib/expoline/Makefile         | 3 +++
     >  arch/s390/lib/{ => expoline}/expoline.S | 0
     >  5 files changed, 12 insertions(+), 4 deletions(-)
     >  create mode 100644 arch/s390/lib/expoline/Makefile
     >  rename arch/s390/lib/{ => expoline}/expoline.S (100%)
     >

     Thanks, Vasily.  We'll test these with OOT and the original gitlab
     pipeline where we spotted potential issue with packaging and report
     back.

Hi,

Successfully tested the first patch in a rhel-9 backport. (had to skip
the second as it has dependencies on other patches like [1] that
deprecated symbols like __LC_BR_R1. Without those, the build resulted in
a flood of: depmod: WARNING: <module>.ko needs unknown symbol __LC_BR_R1.)

For ("s390/nospec: build expoline.o for modules_prepare target"),
Tested-by: C. Erastus Toe <ctoe@xxxxxxxxxx <mailto:ctoe@xxxxxxxxxx>>

[1] 4efd417f298b ("s390: raise minimum supported machine generation to z10")


And then for the entire series (tested on top of v5.19-rc4),
Tested-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>


--
Sumanth



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