linux-kernel - Re: [PATCH/RFC] powerpc/module_64: allow .init

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Date:   Tue, 17 Aug 2021 15:22:38 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Jan Stancek <jstancek@...hat.com>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org,
        linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] powerpc/module_64: allow .init_array constructors to
 run



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@...erman.id.au>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Signed-off-by: Jan Stancek <jstancek@...hat.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,
>