On Fri, Jun 21, 2024 at 12:59:21PM -0400, Joe Lawrence wrote:
> On 6/19/24 14:23, Joe Lawrence wrote:
> > On 6/19/24 13:01, Sumanth Korikkar wrote:
> >> Other Note:
> >> The latest kernel is built with -fPIC and linked with -no-pie (reference
> >> commit: ca888b17da9b ("s390: Compile kernel with -fPIC and link with
> >> -no-pie")) which also avoids generation of dynamic symbols and helps
> >> kpatch usecases (when num of sections >=64k sections). Also the build
> >> options would be similar (-fPIC in kernel and -fPIC in kpatch-build)
> >>
> >> For latest kernel, there is no need to add explicit -fPIC again
> >> in kpatch tool.
> >>
> >> But for the intermediate commits, yes, makes sense to add
> >> it in kpatch-build tools and will create one PR.
> >>
> >
> > Interesting! With 00cda11d3b2e ("s390: Compile kernel with -fPIC and
> > link with -no-pie") it sounds like the original vmlinux would be built
> > with -fPIC as well, so the optimization decisions re: __mmput() would
> > likely be the same. I can retry the tests with v6.10-rcX to verify.
> >
>
> To follow up, all of the kpatch-build integration tests work with
> v6.10.0-rc4 :) as the kernel is built with -fPIC and so are the kpatch
> reference and patched builds. For pre-v6.10 kernels, I think there may
> be some instances where a patch author may need to account for slight
> build differences to appease kpatch-build expectations as I noticed here.
>
> --
> Joe
>
Hi Joe,
I tried bisecting provided rhel config with defconfig, but didnt
succeed yet.
However, I tried using KCFLAGS="-fPIE -mno-pic-data-is-text-relative"
instead of KCFLAGS="-fPIC -mno-pic-data-is-text-relative" and it
generated similar output.
* objdump -Dr -j.text --disassemble=mmput kernel/fork.o
Disassembly of section .text:
00000000000011d0 <mmput>:
11d0: c0 04 00 00 00 00 jgnop 11d0 <mmput>
11d6: a7 18 ff ff lhi %r1,-1
11da: eb 01 21 3c 00 f8 laa %r0,%r1,316(%r2)
11e0: 07 e0 bnor %r0
11e2: ec 08 00 06 01 7e cije %r0,1,11ee <mmput+0x1e>
11e8: c0 f4 00 00 00 00 jg 11e8 <mmput+0x18>
11ea: R_390_PC32DBL __s390_indirect_jump_r14+0x2
11ee: c0 f4 00 00 00 00 jg 11ee <mmput+0x1e>
11f0: R_390_PLT32DBL __mmput+0x2
* KCFLAGS="-fPIE -mno-pic-data-is-text-relative -fno-section-anchors" \
make -s -j$(nproc) kernel/fork.o ;
objdump -Dr -j.text --disassemble=mmput kernel/fork.o
kernel/fork.o: file format elf64-s390
Disassembly of section .text:
0000000000001230 <mmput>:
1230: c0 04 00 00 00 00 jgnop 1230 <mmput>
1236: a7 18 ff ff lhi %r1,-1
123a: eb 01 21 3c 00 f8 laa %r0,%r1,316(%r2)
1240: 07 e0 bnor %r0
1242: ec 08 00 06 01 7e cije %r0,1,124e <mmput+0x1e>
1248: c0 f4 00 00 00 00 jg 1248 <mmput+0x18>
124a: R_390_PC32DBL __s390_indirect_jump_r14+0x2
124e: c0 f4 00 00 00 00 jg 124e <mmput+0x1e>
1250: R_390_PLT32DBL __mmput+0x2
* For commit 778666df60f0 ("s390: compile relocatable kernel without -fPIE"),
"-fPIE -mno-pic-data-is-text-relative" could be used to prevent
confusion to the kpatch tool. I will make changes in the kpatch pull request.
* For latest kernel, both vmlinux and kpatch-build uses -fPIC and
hence no changes are necessary in kpatch tool.
Thank you,
Sumanth
