Re: [PATCH v4] MIPS: don't overlay relocation data with BSS

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Jan 30, 2020 at 08:38:57AM +0100, Oleksij Rempel wrote:
> .bss __rel_start (OVERLAY) was used to optimize RAM size used by
> barebox. Since .bss and __rel_start overlap, we should clear bss only
> after __rel_start was used. Following patch changed initialization
> sequence to clear .bss before __rel_start:
> 1e5aef61fc6a444 ("MIPS: reloc: init bss and cpu")
> 
> This make relocation buffer unusable and broke relocation with different
> symptoms reported by Antony Pavlov <antonynpavlov@gmail.com>:
>   * iomem output has no information on sdram regions, so memtest is unusable;
>   * pc = 0xa081232c, relocation does not work, barebox is located with 8M offset
>     from start of RAM. The board has 256M and relocation routine
>     should move barebox code much higher;
>   * pc = 0xa081232c, so barebox code works from KSEG1 not from KSEG0 as MMU=y option implies.
> 
> There is a choice of moving .bss clear sequence after __rel_start or
> remove this optimization. Since the use of this optimization is minimal
> and danger to trap in to similar issue is still high, i prefer to remove
> this optimization.
> 
> As result of this change, we need to fix calculation of relocation are
> size:
> relocate_code() calculates relocation area size as a sum (barebox_image_size +
> bss_len). barebox_image_size and bss_len are calculated as (__image_end -
> __image_start) and (__bss_stop - __bss_start) respectively. This doesn't take
> into account relocation data placed between  __image_end and __bss_start.
> However relocation preserves BSS position relative to image start, as if
> relocation data is still there. This causes RAM overflow during BSS
> initialization in main_entry(). This problem may be hidden due to the alignment
> of the `relocaddr`.
> 
> Reported-by: Antony Pavlov <antonynpavlov@gmail.com>
> Fixes: 1e5aef61fc6a444 ("MIPS: reloc: init bss and cpu")
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
> ---
>  arch/mips/lib/barebox.lds.S | 2 +-
>  arch/mips/lib/reloc.c       | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)

Applied, thanks

Sascha


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