[U-Boot] [PATCH v2] SPL: tiny-printf: avoid any BSS usage

[Simon Glass]

On 8 July 2016 at 08:18, Andre Przywara <andre.przywara at arm.com> wrote:
> As printf calls may be executed quite early, we should avoid using any
> BSS stored variables, since some boards put BSS in DRAM, which may not
> have been initialised yet.
> Explicitly mark those "static global" variables as belonging to the
> .data section, to keep tiny-printf clear of any BSS usage.
>
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>

Reviewed-by: Simon Glass <sjg at chromium.org>

Another approach would be to put these vars in a struct, declare it as
a local variable and pass it around. But this works OK too.

> ---
> Changes v1 .. v2:
> - remove NO_BSS macro, use __attribute__ ... directly instead
>
>  lib/tiny-printf.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/lib/tiny-printf.c b/lib/tiny-printf.c
> index 451f4f7..b334f05 100644
> --- a/lib/tiny-printf.c
> +++ b/lib/tiny-printf.c
> @@ -13,11 +13,16 @@
>  #include <stdarg.h>
>  #include <serial.h>
>
> -static char *bf;
> -static char zs;
> +/*
> + * This code in here may execute before the DRAM is initialised, so
> + * we should make sure that it doesn't touch BSS, which some boards
> + * put in DRAM.
> + */
> +static char *bf __attribute__ ((section(".data")));
> +static char zs __attribute__ ((section(".data")));
>
>  /* Current position in sprintf() output string */
> -static char *outstr;
> +static char *outstr __attribute__ ((section(".data")));
>
>  static void out(char c)
>  {
> --
> 2.8.2
>