Re: [PATCH v17 4/9] x86/objtool: Add STACK_FRAME_NON_STANDARD macro

[Ingo Molnar <mingo@kernel.org>]

* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> Add a new objtool ignore macro, STACK_FRAME_NON_STANDARD, which can be
> used to tell objtool to skip validation of a function.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
>  MAINTAINERS                   |  1 +
>  arch/x86/kernel/vmlinux.lds.S |  5 ++++-
>  include/linux/objtool.h       | 22 ++++++++++++++++++++++
>  3 files changed, 27 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/objtool.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 7c7cebd..43a940e 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7782,6 +7782,7 @@ OBJTOOL
>  M:	Josh Poimboeuf <jpoimboe@redhat.com>
>  S:	Supported
>  F:	tools/objtool/
> +F:	include/linux/objtool.h
>  
>  OMAP SUPPORT
>  M:	Tony Lindgren <tony@atomide.com>
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 92dc211..6038fe0 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -343,7 +343,10 @@ SECTIONS
>  
>  	/* Sections to be discarded */
>  	DISCARDS
> -	/DISCARD/ : { *(.eh_frame) }
> +	/DISCARD/ : {
> +		*(.eh_frame)
> +		*(__objtool_ignore_*)
> +	}
>  }
>  
>  
> diff --git a/include/linux/objtool.h b/include/linux/objtool.h
> new file mode 100644
> index 0000000..cce9d67
> --- /dev/null
> +++ b/include/linux/objtool.h

So I think this should really be in asm/frame.h, not in an objtool specific 
header.

> @@ -0,0 +1,22 @@
> +#ifndef _LINUX_OBJTOOL_H
> +#define _LINUX_OBJTOOL_H
> +
> +#ifdef CONFIG_STACK_VALIDATION
> +/*
> + * This C macro tells objtool to ignore the function when doing stack metadata
> + * validation.  It should only be used in special cases where you're 100% sure
> + * it won't affect the reliability of frame pointers and kernel stack traces.
> + *
> + * For more information, see tools/objtool/Documentation/stack-validation.txt.
> + */
> +#define STACK_FRAME_NON_STANDARD(_func) \
> +	static void __used __section(__objtool_ignore_func) \
> +		*__objtool_ignore_func_##_func = _func

Likewise, this section should be named __func_non_standard_stack_frame or so, with 
objtool one (but not the only possible) consumer of it.

> +#else /* !CONFIG_STACK_VALIDATION */
> +
> +#define STACK_FRAME_NON_STANDARD(_func)
> +
> +#endif /* CONFIG_STACK_VALIDATION */
> +
> +#endif /* _LINUX_OBJTOOL_H */

The CONFIG_STACK_VALIDATION dependency can be kept.

Thanks,

	Ingo