(In reply to mrwizardwizard from comment #0)
> Created attachment 306623 [details]
> Build log
> 
> Hello,
> 
> when compiling linux kernel 6.9-6.10 with -flto
> 
> compiler outputs:
> 
> ./arch/x86/include/asm/current.h:42:25: error: 'const_pcpu_hot' causes a
> section type conflict with 'pcpu_hot' const_pcpu_hot);
> 

Can you reproduce above on current mainline (v6.11-rc1)?

(In reply to Bagas Sanjaya from comment #1)
> (In reply to mrwizardwizard from comment #0)
> > Created attachment 306623 [details]
> > Build log
> > 
> > Hello,
> > 
> > when compiling linux kernel 6.9-6.10 with -flto
> > 
> > compiler outputs:
> > 
> > ./arch/x86/include/asm/current.h:42:25: error: 'const_pcpu_hot' causes a
> > section type conflict with 'pcpu_hot' const_pcpu_hot);
> > 
> 
> Can you reproduce above on current mainline (v6.11-rc1)?


same messages

mkdir -p /home/mrwizardwizard/Documents/Kernel/linux-6.11-rc1/tools/objtool && make O=/home/mrwizardwizard/Documents/Kernel/linux-6.11-rc1 subdir=tools/objtool --no-print-directory -C objtool 
  INSTALL libsubcmd_headers
  CALL    scripts/checksyscalls.sh
  CC      init/main.o
  AS      arch/x86/entry/entry.o
  AS      arch/x86/entry/entry_64.o
arch/x86/entry/entry_64.o: warning: objtool: __switch_to_asm+0x18: stack layout conflict in alternatives: .altinstr_replacement+0x1d
  CC      arch/x86/entry/syscall_64.o
In file included from ./include/asm-generic/percpu.h:7,
                 from ./arch/x86/include/asm/percpu.h:616,
                 from ./arch/x86/include/asm/current.h:11,
                 from ./arch/x86/include/asm/processor.h:17,
                 from ./arch/x86/include/asm/timex.h:5,
                 from ./include/linux/timex.h:67,
                 from ./include/linux/time32.h:13,
                 from ./include/linux/time.h:60,
                 from ./include/linux/stat.h:19,
                 from ./include/linux/module.h:13,
                 from init/main.c:17:
./arch/x86/include/asm/current.h:42:25: error: 'const_pcpu_hot' causes a section type conflict with 'pcpu_hot'
   42 |                         const_pcpu_hot);
      |                         ^~~~~~~~~~~~~~
./arch/x86/include/asm/current.h:38:42: note: 'pcpu_hot' was declared here
   38 | DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
      |                                          ^~~~~~~~
make[3]: *** [scripts/Makefile.build:244: init/main.o] Error 1
make[2]: *** [scripts/Makefile.build:485: init] Error 2
make[2]: *** Waiting for unfinished jobs....
  CC      arch/x86/entry/common.o
  CC      arch/x86/events/core.o
  CC      arch/x86/entry/vdso/vma.o
In file included from ./include/asm-generic/percpu.h:7,
                 from ./arch/x86/include/asm/percpu.h:616,
                 from ./arch/x86/include/asm/current.h:11,
                 from ./include/linux/sched.h:12,
                 from ./include/linux/ptrace.h:6,
                 from ./include/uapi/asm-generic/bpf_perf_event.h:4,
                 from ./arch/x86/include/generated/uapi/asm/bpf_perf_event.h:1,
                 from ./include/uapi/linux/bpf_perf_event.h:11,
                 from ./include/linux/perf_event.h:18,
                 from arch/x86/events/core.c:15:
./arch/x86/include/asm/current.h:42:25: error: 'const_pcpu_hot' causes a section type conflict with 'pcpu_hot'
   42 |                         const_pcpu_hot);
      |                         ^~~~~~~~~~~~~~
./arch/x86/include/asm/current.h:38:42: note: 'pcpu_hot' was declared here
   38 | DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
      |                                          ^~~~~~~~
make[4]: *** [scripts/Makefile.build:244: arch/x86/events/core.o] Error 1
make[3]: *** [scripts/Makefile.build:485: arch/x86/events] Error 2
make[3]: *** Waiting for unfinished jobs....
  AR      arch/x86/entry/vsyscall/built-in.a
  CC      arch/x86/entry/vdso/extable.o
  LDS     arch/x86/entry/vdso/vdso.lds
  AS      arch/x86/entry/vdso/vdso-note.o
  CC      arch/x86/entry/vdso/vclock_gettime.o
  CC      arch/x86/entry/vdso/vgetcpu.o
  CC      arch/x86/entry/vdso/vgetrandom.o
  AS      arch/x86/entry/vdso/vgetrandom-chacha.o
  HOSTCC  arch/x86/entry/vdso/vdso2c
  VDSO    arch/x86/entry/vdso/vdso64.so.dbg
  OBJCOPY arch/x86/entry/vdso/vdso64.so
  VDSO2C  arch/x86/entry/vdso/vdso-image-64.c
  CC      arch/x86/entry/vdso/vdso-image-64.o
  AR      arch/x86/entry/vdso/built-in.a
  AS      arch/x86/entry/thunk.o
  AR      arch/x86/entry/built-in.a
make[2]: *** [scripts/Makefile.build:485: arch/x86] Error 2
make[1]: *** [/home/mrwizardwizard/Documents/Kernel/linux-6.11-rc1/Makefile:1927: .] Error 2
make: *** [Makefile:224: __sub-make] Error 2

Please attach your .config.

Created attachment 306663 [details]
kernel .config

(In reply to mrwizardwizard from comment #0)

> when compiling linux kernel 6.9-6.10 with -flto

You need a whole lot more patches to successfully compile kernel with GCC LTO. The last revision can be found at:

https://lore.kernel.org/lkml/20221114114344.18650-1-jirislaby@kernel.org/

The patchset defines CONFIG_LTO, which can be used to disable offending optimization, something like the to-be attached patch.

Ideally, a LTO-compatible "const __seg_gs" qualified alias to struct pcpu_hot should be declared, so LTO can retain the disabled optimization, but ...

... the LTO patchset was rejected mainly due to:
- the performance is the same
- the resulting image is bigger
- we need a whole lot of ugly hacks to placate the linker.

Created attachment 306665 [details]
Patch to disable offending optimization for CONFIG_LTO

Untested patch.