diff mbox series

[1/2] padata: Do not mark padata_mt_helper() as __init

Message ID 20221129190123.872394-2-nathan@kernel.org
State New
Headers show
Series Fix lack of section mismatch warnings with LTO | expand

Commit Message

Nathan Chancellor Nov. 29, 2022, 7:01 p.m. UTC
When building arm64 allmodconfig + ThinLTO with clang and a proposed
modpost update to account for -ffuncton-sections, the following warning
appears:

  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@kernel.org>
---
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: linux-crypto@vger.kernel.org
---
 kernel/padata.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Masahiro Yamada Nov. 30, 2022, 10:20 p.m. UTC | #1
On Wed, Nov 30, 2022 at 4:02 AM Nathan Chancellor <nathan@kernel.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 ?)

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@kernel.org>
> ---
> Cc: Steffen Klassert <steffen.klassert@secunet.com>
> Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
> Cc: linux-crypto@vger.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
>
Masahiro Yamada Nov. 30, 2022, 10:35 p.m. UTC | #2
On Wed, Nov 30, 2022 at 4:02 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> When building arm64 allmodconfig + ThinLTO with clang and a proposed
> modpost update to account for -ffuncton-sections, the following warning
> appears:
>
>   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@kernel.org>
> ---
> Cc: Steffen Klassert <steffen.klassert@secunet.com>
> Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
> Cc: linux-crypto@vger.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
>

This patch seems wrong.

padata_work_init() does not reference to padata_mt_helper()


padata_work_alloc_mt() and padata_do_multithreaded() do.
Nathan Chancellor Nov. 30, 2022, 10:37 p.m. UTC | #3
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@kernel.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@kernel.org>
> > ---
> > Cc: Steffen Klassert <steffen.klassert@secunet.com>
> > Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
> > Cc: linux-crypto@vger.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
Daniel Jordan Dec. 6, 2022, 8:15 p.m. UTC | #4
On Thu, Dec 01, 2022 at 07:35:59AM +0900, Masahiro Yamada wrote:
> On Wed, Nov 30, 2022 at 4:02 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > When building arm64 allmodconfig + ThinLTO with clang and a proposed
> > modpost update to account for -ffuncton-sections, the following warning
> > appears:
> >
> >   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@kernel.org>
> > ---
> > Cc: Steffen Klassert <steffen.klassert@secunet.com>
> > Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
> > Cc: linux-crypto@vger.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
> >
> 
> This patch seems wrong.
> 
> padata_work_init() does not reference to padata_mt_helper()
> 
> 
> padata_work_alloc_mt() and padata_do_multithreaded() do.

I see LLVM optimizing padata_work_init by embedding padata_mt_helper's
address in its text, which runs afoul of modpost.

I agree with Masahiro, the warning is a false positive since only __init
functions ever cause the embedded address to be used.

We have __ref for situations like this.  That way, padata_mt_helper can
stay properly __init.
Nathan Chancellor Dec. 7, 2022, 6:58 p.m. UTC | #5
On Tue, Dec 06, 2022 at 03:15:26PM -0500, Daniel Jordan wrote:
> On Thu, Dec 01, 2022 at 07:35:59AM +0900, Masahiro Yamada wrote:
> > On Wed, Nov 30, 2022 at 4:02 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > >
> > > When building arm64 allmodconfig + ThinLTO with clang and a proposed
> > > modpost update to account for -ffuncton-sections, the following warning
> > > appears:
> > >
> > >   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@kernel.org>
> > > ---
> > > Cc: Steffen Klassert <steffen.klassert@secunet.com>
> > > Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
> > > Cc: linux-crypto@vger.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
> > >
> > 
> > This patch seems wrong.
> > 
> > padata_work_init() does not reference to padata_mt_helper()
> > 
> > 
> > padata_work_alloc_mt() and padata_do_multithreaded() do.
> 
> I see LLVM optimizing padata_work_init by embedding padata_mt_helper's
> address in its text, which runs afoul of modpost.
> 
> I agree with Masahiro, the warning is a false positive since only __init
> functions ever cause the embedded address to be used.
> 
> We have __ref for situations like this.  That way, padata_mt_helper can
> stay properly __init.

Ah, thank you for pointing out __ref, that seems to be exactly what we
want here. I will send a v2 marking padata_work_init() as __ref shortly.

Cheers,
Nathan
diff mbox series

Patch

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;