[RFC 1/3] arm: factor out current_stack_pointer

[Mark Rutland]

On Thu, Mar 15, 2018 at 05:08:57PM +0000, Zubin Mithra wrote:
> Multiple header files that rely on current_stack_pointer do not have the
> necessary include <asm/thread_info.h>, and are thus fragile to changes
> in the header soup.
> 
> Subsequent patches will affect the header soup such that including
> <asm/thread_info.h> will result in a circular header include. Factor
> current_thread_info into its own header and have all the users include
> this header explicitely.

Nit: s/explicitely/explicitly/

> Signed-off-by: Zubin Mithra <zsm at chromium.org>

I can't remember precisely what the circular include dependency was that
necessitated this for arm64, but regardless this looks reasonable to me.
FWIW:

Acked-by: Mark Rutland <mark.rutland at arm.com>

... though we'll need the rest of the THREAD_INFO_IN_TASK patches for
this to be a worthwhile change.

Thanks,
Mark.

> ---
>  arch/arm/include/asm/percpu.h        | 2 ++
>  arch/arm/include/asm/stack_pointer.h | 9 +++++++++
>  arch/arm/include/asm/thread_info.h   | 6 +-----
>  arch/arm/kernel/return_address.c     | 1 +
>  arch/arm/kernel/stacktrace.c         | 1 +
>  arch/arm/kernel/unwind.c             | 1 +
>  6 files changed, 15 insertions(+), 5 deletions(-)
>  create mode 100644 arch/arm/include/asm/stack_pointer.h
> 
> diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
> index a89b4076cde4..6a19e634d0cf 100644
> --- a/arch/arm/include/asm/percpu.h
> +++ b/arch/arm/include/asm/percpu.h
> @@ -16,6 +16,8 @@
>  #ifndef _ASM_ARM_PERCPU_H_
>  #define _ASM_ARM_PERCPU_H_
>  
> +#include <asm/stack_pointer.h>
> +
>  /*
>   * Same as asm-generic/percpu.h, except that we store the per cpu offset
>   * in the TPIDRPRW. TPIDRPRW only exists on V6K and V7
> diff --git a/arch/arm/include/asm/stack_pointer.h b/arch/arm/include/asm/stack_pointer.h
> new file mode 100644
> index 000000000000..5a6a8c6d9208
> --- /dev/null
> +++ b/arch/arm/include/asm/stack_pointer.h
> @@ -0,0 +1,9 @@
> +#ifndef __ASM_STACK_POINTER_H
> +#define __ASM_STACK_POINTER_H
> +
> +/*
> + * how to get the current stack pointer in C
> + */
> +register unsigned long current_stack_pointer asm ("sp");
> +
> +#endif
> diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
> index e71cc35de163..56317024d221 100644
> --- a/arch/arm/include/asm/thread_info.h
> +++ b/arch/arm/include/asm/thread_info.h
> @@ -25,6 +25,7 @@
>  struct task_struct;
>  
>  #include <asm/types.h>
> +#include <asm/stack_pointer.h>
>  
>  typedef unsigned long mm_segment_t;
>  
> @@ -75,11 +76,6 @@ struct thread_info {
>  	.addr_limit	= KERNEL_DS,					\
>  }
>  
> -/*
> - * how to get the current stack pointer in C
> - */
> -register unsigned long current_stack_pointer asm ("sp");
> -
>  /*
>   * how to get the thread information struct from C
>   */
> diff --git a/arch/arm/kernel/return_address.c b/arch/arm/kernel/return_address.c
> index 36ed35073289..d76e64250816 100644
> --- a/arch/arm/kernel/return_address.c
> +++ b/arch/arm/kernel/return_address.c
> @@ -14,6 +14,7 @@
>  #if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
>  #include <linux/sched.h>
>  
> +#include <asm/stack_pointer.h>
>  #include <asm/stacktrace.h>
>  
>  struct return_address_data {
> diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
> index a56e7c856ab5..d519b8e0797f 100644
> --- a/arch/arm/kernel/stacktrace.c
> +++ b/arch/arm/kernel/stacktrace.c
> @@ -4,6 +4,7 @@
>  #include <linux/stacktrace.h>
>  
>  #include <asm/sections.h>
> +#include <asm/stack_pointer.h>
>  #include <asm/stacktrace.h>
>  #include <asm/traps.h>
>  
> diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
> index 0bee233fef9a..860f8ac187e0 100644
> --- a/arch/arm/kernel/unwind.c
> +++ b/arch/arm/kernel/unwind.c
> @@ -45,6 +45,7 @@
>  #include <linux/spinlock.h>
>  #include <linux/list.h>
>  
> +#include <asm/stack_pointer.h>
>  #include <asm/stacktrace.h>
>  #include <asm/traps.h>
>  #include <asm/unwind.h>
> -- 
> 2.16.2.804.g6dcf76e118-goog
>