[U-Boot] [RFC] bug.h: Drop filename from BUG/WARNING logs if building for TPL/SPL

[Andreas Dannenberg]

On Wed, Jul 10, 2019 at 04:30:44PM -0500, Andreas Dannenberg wrote:
> On several platforms space is very tight when building for SPL or TPL.
> To claw back a few bytes to be used for code remove the __FILE__ name
> from the BUG() and WARN() type macros. Since those macros still print
> the function name plus a line number this should not really affect
> the ability to backtrace an actual BUG/WARN message to a specific
> piece of code.
> 
> Signed-off-by: Andreas Dannenberg <dannenberg at ti.com>
> ---
> 
> I was looking for a way to shave off a few bytes from the SPL code size
> (TI AM335x) and looking at the hexdump of the SPL I found well why not
> further reduce some strings down in size... I was already aware of the
> recent compiler optimizations to drop some of the irrelevant path from
> the __FILE__ macro but I wanted to go one step beyond this. Dropping
> all the path from __FILE__ via preprocessor macro can't be easily done
> as others have already found so I decided to drop __FILE__ altogether
> (code below) and was excited about the improvements I got...

Just some quick examples about the savings...

Using buildman "bloat" reporting (-B) I see the SPL .text size for AM335x
to be reduced by 12 bytes. And for AM43xx the size goes down by 52
bytes. The benefit of the proposed change really depends on a) whether a
given platform uses SPL, and b) how many calls to BUG/WARN it has. The
USB drivers in AM335x/AM43xx are really the "heavy hitters" here. I'm
sure I could find additional examples/platforms to highlight savings if
needed.

Anyways I'm not proud of the proposed change but merely wanted to see
with this RFC if there isn't any way to do further optimizations on the
__FILE__ topic that are not overly intrusive specifically as it comes to
SPL.

Best Regards,
Andreas


> 
> Then of course using Google I found there was prior art, specifically
> this discussion here:
> 
> "[U-Boot] __FILE__ usage and and SPL limits for SRAM"
> https://patchwork.ozlabs.org/patch/746922/
> 
> 
> So I made this submission to "RFC" to simply re-ignite the subject to
> see if we can somehow find some path to proceed with such a change...
> 
> I like about the proposal referenced above that it touches more places
> than what I came up with, however it is missing the TPL/SPL aspect
> which I thought would be a good way to alleviate some of the concerns
> raised (Wolfgang) around not having __FILE__ in the log...
> 
> Maybe a combination of the approaches could be workable?
> 
> At the end of the day SPL/TPL are intended for very memory-constrained
> environments, so I feel changes like the proposed that don't really
> affect any of the existing functionality are good candidates to
> consider...
> 
> Regards,
> Andreas
> 
>  include/linux/bug.h | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/bug.h b/include/linux/bug.h
> index 29f84168a3..36b5fddfae 100644
> --- a/include/linux/bug.h
> +++ b/include/linux/bug.h
> @@ -5,9 +5,22 @@
>  #include <linux/build_bug.h>
>  #include <linux/compiler.h>
>  #include <linux/printk.h>
> +#include <linux/kconfig.h>
> +
> +#if defined(CONFIG_TPL_BUILD) || defined(CONFIG_SPL_BUILD)
> +/*
> + * In case of TPL/SPL use a short format not including __FILE__
> + * to reduce image size
> + */
> +#define BUG_WARN_LOC_FMT	"%d@%s()"
> +#define BUG_WARN_LOC_ARGS	__LINE__, __func__
> +#else
> +#define BUG_WARN_LOC_FMT	"%s:%d/%s()"
> +#define BUG_WARN_LOC_ARGS	__FILE__, __LINE__, __func__
> +#endif
>  
>  #define BUG() do { \
> -	printk("BUG at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
> +	printk("BUG at " BUG_WARN_LOC_FMT "!\n", BUG_WARN_LOC_ARGS);	\
>  	panic("BUG!"); \
>  } while (0)
>  
> @@ -16,7 +29,7 @@
>  #define WARN_ON(condition) ({						\
>  	int __ret_warn_on = !!(condition);				\
>  	if (unlikely(__ret_warn_on))					\
> -		printk("WARNING at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
> +		printk("WARNING at " BUG_WARN_LOC_FMT "!\n", BUG_WARN_LOC_ARGS); \
>  	unlikely(__ret_warn_on);					\
>  })
>  
> -- 
> 2.17.1
>