[v2] ARM: atags_to_fdt: don't warn about stack size

Commit Message

Arnd Bergmann Feb. 18, 2016, 4:26 p.m. UTC

The merge_fdt_bootargs() function by definition consumes more than 1024
bytes of stack because it has a 1024 byte command line on the stack,
meaning that we always get a warning when building this file:

arch/arm/boot/compressed/atags_to_fdt.c: In function 'merge_fdt_bootargs':
arch/arm/boot/compressed/atags_to_fdt.c:98:1: warning: the frame size of 1032 bytes is larger than 1024 bytes [-Wframe-larger-than=]

However, as this is the decompressor and we know that it has a very shallow
call chain, and we do not actually risk overflowing the kernel stack
at runtime here.

This just shuts up the warning by slightly increasing the limit for this
file.

Signed-off-by: Arnd Bergmann <[e-mail]>
---
On Thursday 18 February 2016 11:13:52 Nicolas Pitre wrote:
> What about setting the warning to 2048 instead?

Sure, actually 1280 is more than enough I think.

Comments

Nicolas Pitre Feb. 18, 2016, 5:14 p.m. UTC | #1

On Thu, 18 Feb 2016, Arnd Bergmann wrote:

> The merge_fdt_bootargs() function by definition consumes more than 1024
> bytes of stack because it has a 1024 byte command line on the stack,
> meaning that we always get a warning when building this file:
> 
> arch/arm/boot/compressed/atags_to_fdt.c: In function 'merge_fdt_bootargs':
> arch/arm/boot/compressed/atags_to_fdt.c:98:1: warning: the frame size of 1032 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> 
> However, as this is the decompressor and we know that it has a very shallow
> call chain, and we do not actually risk overflowing the kernel stack
> at runtime here.
> 
> This just shuts up the warning by slightly increasing the limit for this
> file.
> 
> Signed-off-by: Arnd Bergmann <[e-mail]>

Acked-by: Nicolas Pitre <[e-mail]>


> ---
> On Thursday 18 February 2016 11:13:52 Nicolas Pitre wrote:
> > What about setting the warning to 2048 instead?
> 
> Sure, actually 1280 is more than enough I think.
> 
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 7a6a58ef8aaf..2cc63038d6c8 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -85,6 +85,8 @@ $(addprefix $(obj)/,$(libfdt) $(libfdt_hdrs)): $(obj)/%: $(srctree)/scripts/dtc/
>  $(addprefix $(obj)/,$(libfdt_objs) atags_to_fdt.o): \
>  	$(addprefix $(obj)/,$(libfdt_hdrs))
>  
> +CFLAGS_atags_to_fdt.o += -Wframe-larger-than=1280
> +
>  ifeq ($(CONFIG_ARM_ATAG_DTB_COMPAT),y)
>  OBJS	+= $(libfdt_objs) atags_to_fdt.o
>  endif
> 
>

Arnd Bergmann Feb. 19, 2016, 4:58 p.m. UTC | #2

On Thursday 18 February 2016 17:26:56 Arnd Bergmann wrote:
> On Thursday 18 February 2016 11:13:52 Nicolas Pitre wrote:
> > What about setting the warning to 2048 instead?
> 
> Sure, actually 1280 is more than enough I think.
> 
It turns out that doesn't fix the problem though, as the new
argument gets prepended and the existing flag overrides it.

I have modified the patch now to do both:

CFLAGS_REMOVE_atags_to_fdt.o += -Wframe-larger-than=${CONFIG_FRAME_WARN}
CFLAGS_atags_to_fdt.o += -Wframe-larger-than=1280

	Arnd

Patch

diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 7a6a58ef8aaf..2cc63038d6c8 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -85,6 +85,8 @@  $(addprefix $(obj)/,$(libfdt) $(libfdt_hdrs)): $(obj)/%: $(srctree)/scripts/dtc/
 $(addprefix $(obj)/,$(libfdt_objs) atags_to_fdt.o): \
 	$(addprefix $(obj)/,$(libfdt_hdrs))
 
+CFLAGS_atags_to_fdt.o += -Wframe-larger-than=1280
+
 ifeq ($(CONFIG_ARM_ATAG_DTB_COMPAT),y)
 OBJS	+= $(libfdt_objs) atags_to_fdt.o
 endif