Re: ppc64le vmlinuz is huge when building with BTF

Re: ppc64le vmlinuz is huge when building with BTF

[Naveen N Rao]

[Cc linuxppc-dev]

Dominique Martinet wrote:
> 
> Alan Maguire wrote on Thu, Jun 15, 2023 at 03:31:49PM +0100:
>> However the problem I suspect is this:
>> 
>>  51 .debug_info   0a488b55  0000000000000000  0000000000000000  026f8d20
>>  2**0
>>                   CONTENTS, READONLY, DEBUGGING
>> [...]
>> 
>> The debug info hasn't been stripped, so I suspect the packaging spec
>> file or equivalent - in perhaps trying to preserve the .BTF section -
>> is preserving debug info too. DWARF needs to be there at BTF
>> generation time in vmlinux but is usually stripped for non-debug
>> packages.
> 
> Thanks Alan and Eduard!
> I guess I should have checked that first, it helps.
> 
> We're not stripping anything in vmlinuz for other archs -- the linker
> script already should be including only the bare minimum to decompress
> itself (+compressed useful bits), so I guess it's a Kbuild issue for the
> arch.

For a related discussion, see:
http://lore.kernel.org/CAK18DXZKs2PNmLndeGYqkPxmrrBR=6ca3bhyYCj=GhyA7dHfAQ@mail.gmail.com

> We can add a strip but I unfortunately have no way of testing ppc build,
> I'll ask around the build linux-kbuild and linuxppc-dev lists if that's
> expected; it shouldn't be that bad now that's figured out.

Stripping vmlinux would indeed be the way to go. As mentioned in the 
above link, fedora also packages a strip'ed vmlinux for ppc64le:
https://src.fedoraproject.org/rpms/kernel/blob/4af17bffde7a1eca9ab164e5de0e391c277998a4/f/kernel.spec#_1797


- Naveen

Re: ppc64le vmlinuz is huge when building with BTF

[Dominique Martinet]

Naveen N Rao wrote on Fri, Jun 16, 2023 at 04:28:53PM +0530:
> > We're not stripping anything in vmlinuz for other archs -- the linker
> > script already should be including only the bare minimum to decompress
> > itself (+compressed useful bits), so I guess it's a Kbuild issue for the
> > arch.
> 
> For a related discussion, see:
> http://lore.kernel.org/CAK18DXZKs2PNmLndeGYqkPxmrrBR=6ca3bhyYCj=GhyA7dHfAQ@mail.gmail.com

Thanks, I didn't know that ppc64le boots straight into vmlinux, as 'make
install' somehow installs something called 'vmlinuz-lts' (-lts coming
out of localversion afaiu, but vmlinuz would come from the build
scripts) ; this is somewhat confusing as vmlinuz on other archs is a
compressed/pre-processed binary so I'd expect it to at least be
stripped...

> > We can add a strip but I unfortunately have no way of testing ppc build,
> > I'll ask around the build linux-kbuild and linuxppc-dev lists if that's
> > expected; it shouldn't be that bad now that's figured out.
> 
> Stripping vmlinux would indeed be the way to go. As mentioned in the above
> link, fedora also packages a strip'ed vmlinux for ppc64le:
> https://src.fedoraproject.org/rpms/kernel/blob/4af17bffde7a1eca9ab164e5de0e391c277998a4/f/kernel.spec#_1797

It feels somewhat wrong to add a strip just for ppc64le after make
install, but I guess we probably ought to do the same...
I don't have any hardware to test booting the result though, I'll submit
an update and ask for someone to test when it's done.
(bit busy but that doesn't take long, will do that tomorrow morning
before I forget)

Thanks!
-- 
Dominique Martinet | Asmadeus

Re: ppc64le vmlinuz is huge when building with BTF

[Naveen N Rao]

Dominique Martinet wrote:
> Naveen N Rao wrote on Fri, Jun 16, 2023 at 04:28:53PM +0530:
>> > We're not stripping anything in vmlinuz for other archs -- the linker
>> > script already should be including only the bare minimum to decompress
>> > itself (+compressed useful bits), so I guess it's a Kbuild issue for the
>> > arch.
>> 
>> For a related discussion, see:
>> http://lore.kernel.org/CAK18DXZKs2PNmLndeGYqkPxmrrBR=6ca3bhyYCj=GhyA7dHfAQ@mail.gmail.com
> 
> Thanks, I didn't know that ppc64le boots straight into vmlinux, as 'make
> install' somehow installs something called 'vmlinuz-lts' (-lts coming
> out of localversion afaiu, but vmlinuz would come from the build
> scripts) ; this is somewhat confusing as vmlinuz on other archs is a
> compressed/pre-processed binary so I'd expect it to at least be
> stripped...

As far as I can tell, kernel's install script doesn't give out that 
name, so 'vmlinuz' is likely coming from the distro's 
/[s]bin/installkernel script. It probably needs an override to retain 
'vmlinux'. 

> 
>> > We can add a strip but I unfortunately have no way of testing ppc build,
>> > I'll ask around the build linux-kbuild and linuxppc-dev lists if that's
>> > expected; it shouldn't be that bad now that's figured out.
>> 
>> Stripping vmlinux would indeed be the way to go. As mentioned in the above
>> link, fedora also packages a strip'ed vmlinux for ppc64le:
>> https://src.fedoraproject.org/rpms/kernel/blob/4af17bffde7a1eca9ab164e5de0e391c277998a4/f/kernel.spec#_1797
> 
> It feels somewhat wrong to add a strip just for ppc64le after make
> install, but I guess we probably ought to do the same...
> I don't have any hardware to test booting the result though, I'll submit
> an update and ask for someone to test when it's done.
> (bit busy but that doesn't take long, will do that tomorrow morning
> before I forget)

Thanks! You're right that it's likely just powerpc that is different 
here. It sure would be nice if we can iron out issues with our zImage.


- Naveen