Re: [RFC PATCH 4/4] kernel: add support for init_array constructors

[Peter Oberparleiter <oberpar@linux.vnet.ibm.com>]

On 23.08.2013 10:39, Frantisek Hrbata wrote:
> This adds the .init_array section as yet another section with constructors. This
> is needed because gcc is adding __gcov_init calls to .init_array.
> 
> Signed-off-by: Frantisek Hrbata <fhrbata@redhat.com>
> ---
>  include/asm-generic/vmlinux.lds.h | 1 +
>  include/linux/module.h            | 2 ++
>  kernel/module.c                   | 6 ++++++
>  3 files changed, 9 insertions(+)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 69732d2..c55d8d9 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -468,6 +468,7 @@
>  #define KERNEL_CTORS()	. = ALIGN(8);			   \
>  			VMLINUX_SYMBOL(__ctors_start) = .; \
>  			*(.ctors)			   \
> +			*(.init_array)			   \

This is exactly how I (would) have done it.

>  			VMLINUX_SYMBOL(__ctors_end) = .;
>  #else
>  #define KERNEL_CTORS()
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 46f1ea0..89ff829 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -374,6 +374,8 @@ struct module
>  	/* Constructor functions. */
>  	ctor_fn_t *ctors;
>  	unsigned int num_ctors;
> +	ctor_fn_t *init_array;
> +	unsigned int num_init_array;

I think it would be safe to re-use the ctors-related fields here. Each GCC
version will only ever create either of .ctors or .init_array, but never
both. The only case where separate fields would be required, would be when
linking a kernel module from multiple object files compiled with different
versions of GCC.

>  #endif
>  };
>  #ifndef MODULE_ARCH_INIT
> diff --git a/kernel/module.c b/kernel/module.c
> index 2069158..581ae89 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2760,6 +2760,9 @@ static void find_module_sections(struct module *mod, struct load_info *info)
>  #ifdef CONFIG_CONSTRUCTORS
>  	mod->ctors = section_objs(info, ".ctors",
>  				  sizeof(*mod->ctors), &mod->num_ctors);

When reusing mod->ctors, you could check for mod->ctors == NULL here and
fill in the values from section_objs(".init_array").

> +	mod->init_array = section_objs(info, ".init_array",
> +				  sizeof(*mod->init_array),
> +				  &mod->num_init_array);
>  #endif
> 
>  #ifdef CONFIG_TRACEPOINTS
> @@ -3024,6 +3027,9 @@ static void do_mod_ctors(struct module *mod)
> 
>  	for (i = 0; i < mod->num_ctors; i++)
>  		mod->ctors[i]();
> +
> +	for (i = 0; i < mod->num_init_array; i++)
> +		mod->init_array[i]();
>  #endif
>  }
> 

-- 
Peter Oberparleiter
Linux on System z Development - IBM Germany