[PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

[PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

[Jan Stancek]

gcov and kasan rely on compiler generated constructor code.
For modules, gcc-8 with gcov enabled generates .init_array section,
but on ppc64le it doesn't get executed. find_module_sections() never
finds .init_array section, because module_frob_arch_sections() renames
it to _init_array.

Avoid renaming .init_array section, so do_mod_ctors() can use it.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
I wasn't able to trace the comment:
  "We don't handle .init for the moment: rename to _init"
to original patch (it pre-dates .git). I'm not sure if it
still applies today, so I limited patch to .init_array. This
fixes gcov for modules for me on ppc64le 5.14.0-rc6.

Renaming issue is also mentioned in kasan patches here:
  https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210319144058.772525-1-dja@axtens

 arch/powerpc/kernel/module_64.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 6baa676e7cb6..c604b13ea6bf 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -299,8 +299,16 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
 					  sechdrs[i].sh_size);
 
 		/* We don't handle .init for the moment: rename to _init */
-		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
+		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init"))) {
+#ifdef CONFIG_CONSTRUCTORS
+			/* find_module_sections() needs .init_array intact */
+			if (strstr(secstrings + sechdrs[i].sh_name,
+				".init_array")) {
+				break;
+			}
+#endif
 			p[0] = '_';
+		}
 
 		if (sechdrs[i].sh_type == SHT_SYMTAB)
 			dedotify((void *)hdr + sechdrs[i].sh_offset,
-- 
2.27.0

Re: [PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

[Christophe Leroy]

Le 17/08/2021 à 15:02, Jan Stancek a écrit :
> gcov and kasan rely on compiler generated constructor code.
> For modules, gcc-8 with gcov enabled generates .init_array section,
> but on ppc64le it doesn't get executed. find_module_sections() never
> finds .init_array section, because module_frob_arch_sections() renames
> it to _init_array.
> 
> Avoid renaming .init_array section, so do_mod_ctors() can use it.
> 
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
> I wasn't able to trace the comment:
>    "We don't handle .init for the moment: rename to _init"

Original patch there: https://github.com/mpe/linux-fullhistory/commit/d6ad6690aa72

> to original patch (it pre-dates .git). I'm not sure if it
> still applies today, so I limited patch to .init_array. This
> fixes gcov for modules for me on ppc64le 5.14.0-rc6.
> 
> Renaming issue is also mentioned in kasan patches here:
>    https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210319144058.772525-1-dja@axtens
> 
>   arch/powerpc/kernel/module_64.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 6baa676e7cb6..c604b13ea6bf 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -299,8 +299,16 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
>   					  sechdrs[i].sh_size);
>   
>   		/* We don't handle .init for the moment: rename to _init */
> -		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
> +		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init"))) {
> +#ifdef CONFIG_CONSTRUCTORS

Please avoid #ifdefery as much as possible.

I think here you can do:

			if (IS_ENABLED(CONFIG_CONSTRUCTORS) &&
			    strstr(secstrings + sechdrs[i].sh_name, ".init_array"))

> +			/* find_module_sections() needs .init_array intact */
> +			if (strstr(secstrings + sechdrs[i].sh_name,
> +				".init_array")) {

No { } for single statements (See 
https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces)

> +				break;
> +			}
> +#endif
>   			p[0] = '_';
> +		}
>   
>   		if (sechdrs[i].sh_type == SHT_SYMTAB)
>   			dedotify((void *)hdr + sechdrs[i].sh_offset,
> 

Re: [PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

[Daniel Axtens]

Jan Stancek <jstancek@redhat.com> writes:

> gcov and kasan rely on compiler generated constructor code.
> For modules, gcc-8 with gcov enabled generates .init_array section,
> but on ppc64le it doesn't get executed. find_module_sections() never
> finds .init_array section, because module_frob_arch_sections() renames
> it to _init_array.
>
> Avoid renaming .init_array section, so do_mod_ctors() can use it.

This (the existing renaming) breaks a KASAN test too, so I'd love to see
this fixed.

However, I don't know that renaming the section is a complete fix: from
memory it is still be possible to get relocations that are too far away
and require separate trampolines. But I wasn't able to construct a
module that exhibited this behaviour and test a fix before I got pulled
away to other things.

Kind regards,
Daniel

>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
> I wasn't able to trace the comment:
>   "We don't handle .init for the moment: rename to _init"
> to original patch (it pre-dates .git). I'm not sure if it
> still applies today, so I limited patch to .init_array. This
> fixes gcov for modules for me on ppc64le 5.14.0-rc6.
>
> Renaming issue is also mentioned in kasan patches here:
>   https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210319144058.772525-1-dja@axtens
>
>  arch/powerpc/kernel/module_64.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 6baa676e7cb6..c604b13ea6bf 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -299,8 +299,16 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
>  					  sechdrs[i].sh_size);
>  
>  		/* We don't handle .init for the moment: rename to _init */
> -		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
> +		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init"))) {
> +#ifdef CONFIG_CONSTRUCTORS
> +			/* find_module_sections() needs .init_array intact */
> +			if (strstr(secstrings + sechdrs[i].sh_name,
> +				".init_array")) {
> +				break;
> +			}
> +#endif
>  			p[0] = '_';
> +		}
>  
>  		if (sechdrs[i].sh_type == SHT_SYMTAB)
>  			dedotify((void *)hdr + sechdrs[i].sh_offset,
> -- 
> 2.27.0

Re: [PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

[Christophe Leroy]

Le 17/08/2021 à 15:02, Jan Stancek a écrit :
> gcov and kasan rely on compiler generated constructor code.
> For modules, gcc-8 with gcov enabled generates .init_array section,
> but on ppc64le it doesn't get executed. find_module_sections() never
> finds .init_array section, because module_frob_arch_sections() renames
> it to _init_array.
> 
> Avoid renaming .init_array section, so do_mod_ctors() can use it.
> 
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>

Does commit d4be60fe66b7 ("powerpc/module_64: use module_init_section 
instead of patching names") fixes your issue ?

If not, please rebase and resubmit.

Thanks
Christophe


> ---
> I wasn't able to trace the comment:
>    "We don't handle .init for the moment: rename to _init"
> to original patch (it pre-dates .git). I'm not sure if it
> still applies today, so I limited patch to .init_array. This
> fixes gcov for modules for me on ppc64le 5.14.0-rc6.
> 
> Renaming issue is also mentioned in kasan patches here:
>    https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210319144058.772525-1-dja@axtens
> 
>   arch/powerpc/kernel/module_64.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 6baa676e7cb6..c604b13ea6bf 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -299,8 +299,16 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
>   					  sechdrs[i].sh_size);
>   
>   		/* We don't handle .init for the moment: rename to _init */
> -		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
> +		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init"))) {
> +#ifdef CONFIG_CONSTRUCTORS
> +			/* find_module_sections() needs .init_array intact */
> +			if (strstr(secstrings + sechdrs[i].sh_name,
> +				".init_array")) {
> +				break;
> +			}
> +#endif
>   			p[0] = '_';
> +		}
>   
>   		if (sechdrs[i].sh_type == SHT_SYMTAB)
>   			dedotify((void *)hdr + sechdrs[i].sh_offset,

Re: [PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

[Jan Stancek]

On Thu, Jul 7, 2022 at 1:20 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 17/08/2021 à 15:02, Jan Stancek a écrit :
> > gcov and kasan rely on compiler generated constructor code.
> > For modules, gcc-8 with gcov enabled generates .init_array section,
> > but on ppc64le it doesn't get executed. find_module_sections() never
> > finds .init_array section, because module_frob_arch_sections() renames
> > it to _init_array.
> >
> > Avoid renaming .init_array section, so do_mod_ctors() can use it.
> >
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Paul Mackerras <paulus@samba.org>
> > Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> > Signed-off-by: Jan Stancek <jstancek@redhat.com>
>
> Does commit d4be60fe66b7 ("powerpc/module_64: use module_init_section
> instead of patching names") fixes your issue ?

Yes, it does gcov for me. Thanks

>
> If not, please rebase and resubmit.
>
> Thanks
> Christophe
>
>
> > ---
> > I wasn't able to trace the comment:
> >    "We don't handle .init for the moment: rename to _init"
> > to original patch (it pre-dates .git). I'm not sure if it
> > still applies today, so I limited patch to .init_array. This
> > fixes gcov for modules for me on ppc64le 5.14.0-rc6.
> >
> > Renaming issue is also mentioned in kasan patches here:
> >    https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210319144058.772525-1-dja@axtens
> >
> >   arch/powerpc/kernel/module_64.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> > index 6baa676e7cb6..c604b13ea6bf 100644
> > --- a/arch/powerpc/kernel/module_64.c
> > +++ b/arch/powerpc/kernel/module_64.c
> > @@ -299,8 +299,16 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
> >                                         sechdrs[i].sh_size);
> >
> >               /* We don't handle .init for the moment: rename to _init */
> > -             while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
> > +             while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init"))) {
> > +#ifdef CONFIG_CONSTRUCTORS
> > +                     /* find_module_sections() needs .init_array intact */
> > +                     if (strstr(secstrings + sechdrs[i].sh_name,
> > +                             ".init_array")) {
> > +                             break;
> > +                     }
> > +#endif
> >                       p[0] = '_';
> > +             }
> >
> >               if (sechdrs[i].sh_type == SHT_SYMTAB)
> >                       dedotify((void *)hdr + sechdrs[i].sh_offset,
>