linux-kernel - Re: [PATCH 1/2] padata: Do not mark padata_mt_helper() as _

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Date:   Wed, 30 Nov 2022 15:37:55 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Nicolas Schier <nicolas@...sle.eu>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Vincent Donnefort <vdonnefort@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux-crypto@...r.kernel.org
Subject: Re: [PATCH 1/2] padata: Do not mark padata_mt_helper() as __init

On Thu, Dec 01, 2022 at 07:20:47AM +0900, Masahiro Yamada wrote:
> On Wed, Nov 30, 2022 at 4:02 AM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > When building arm64 allmodconfig + ThinLTO with clang and a proposed
> > modpost update to account for -ffuncton-sections, the following warning
> > appears:
> 
> 
> 
> How to enable -ffuncton-sections for ARCH=arm64 ?
> (in other words, how to set CONFIG_LD_DEAD_CODE_DATA_ELIMINATION ?)

clang LTO implies -fdata-sections and -ffunction-sections.

$ cat foo.c
int foo(void)
{
        return 0;
}

$ cat bar.c
extern int foo(void);

int bar(void)
{
        return foo();
}

$ clang -c -o foo.{o,c}
$ clang -c -o bar.{o,c}
$ ld.lld -r -o foobar {foo,bar}.o
$ llvm-readelf -s foobar

Symbol table '.symtab' contains 9 entries:
   Num:    Value          Size Type    Bind   Vis       Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
     1: 0000000000000000     0 FILE    LOCAL  DEFAULT   ABS foo.c
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT     1 .text
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT     3 .eh_frame
     4: 0000000000000000     0 SECTION LOCAL  DEFAULT     5 .llvm_addrsig
     5: 0000000000000000     0 FILE    LOCAL  DEFAULT   ABS bar.c
     6: 0000000000000000     0 SECTION LOCAL  DEFAULT     2 .comment
     7: 0000000000000000     8 FUNC    GLOBAL DEFAULT     1 foo
     8: 0000000000000010    11 FUNC    GLOBAL DEFAULT     1 bar

$ clang -flto -c -o foo.{o,c}
$ clang -flto -c -o bar.{o,c}
$ ld.lld -r -o foobar {foo,bar}.o
$ llvm-readelf -s foobar

Symbol table '.symtab' contains 10 entries:
   Num:    Value          Size Type    Bind   Vis       Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
     1: 0000000000000000     0 FILE    LOCAL  DEFAULT   ABS ld-temp.o
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT     1 .text
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT     2 .text.foo
     4: 0000000000000000     0 SECTION LOCAL  DEFAULT     3 .text.bar
     5: 0000000000000000     0 SECTION LOCAL  DEFAULT     6 .eh_frame
     6: 0000000000000000     0 SECTION LOCAL  DEFAULT     8 .llvm_addrsig
     7: 0000000000000000     0 SECTION LOCAL  DEFAULT     5 .comment
     8: 0000000000000000     8 FUNC    GLOBAL DEFAULT     2 foo
     9: 0000000000000000    13 FUNC    GLOBAL DEFAULT     3 bar

> In upstream, it is only possible for mips and powerpc.
> 
> ./arch/mips/Kconfig:82: select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
> ./arch/powerpc/Kconfig:237: select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
> 
> 
> 
> Is there another proposal to add it for arm64,
> or is this about a downstream kernel?
> 
> 
> 
> 
> 
> >
> >   WARNING: modpost: vmlinux.o: section mismatch in reference: padata_work_init (section: .text.padata_work_init) -> padata_mt_helper (section: .init.text)
> >   WARNING: modpost: vmlinux.o: section mismatch in reference: padata_work_init (section: .text.padata_work_init) -> padata_mt_helper (section: .init.text)
> >
> > In both cases, an __init function calls padata_work_init(), which is not
> > marked __init, with padata_mt_helper(), another __init function, as a
> > work function argument.
> >
> > padata_work_init() is called from non-init paths, otherwise it could be
> > marked __init to resolve the warning. Instead, remove __init from
> > padata_mt_helper() to resolve the warning.
> >
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> > Cc: Steffen Klassert <steffen.klassert@...unet.com>
> > Cc: Daniel Jordan <daniel.m.jordan@...cle.com>
> > Cc: linux-crypto@...r.kernel.org
> > ---
> >  kernel/padata.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/padata.c b/kernel/padata.c
> > index e5819bb8bd1d..c2271d7e446d 100644
> > --- a/kernel/padata.c
> > +++ b/kernel/padata.c
> > @@ -45,7 +45,7 @@ struct padata_mt_job_state {
> >  };
> >
> >  static void padata_free_pd(struct parallel_data *pd);
> > -static void __init padata_mt_helper(struct work_struct *work);
> > +static void padata_mt_helper(struct work_struct *work);
> >
> >  static int padata_index_to_cpu(struct parallel_data *pd, int cpu_index)
> >  {
> > @@ -425,7 +425,7 @@ static int padata_setup_cpumasks(struct padata_instance *pinst)
> >         return err;
> >  }
> >
> > -static void __init padata_mt_helper(struct work_struct *w)
> > +static void padata_mt_helper(struct work_struct *w)
> >  {
> >         struct padata_work *pw = container_of(w, struct padata_work, pw_work);
> >         struct padata_mt_job_state *ps = pw->pw_data;
> > --
> > 2.38.1
> >
> 
> 
> -- 
> Best Regards
> Masahiro Yamada