Re: RISC-V: erizo: large gap between bss and stack regions

[Sascha Hauer <sha@pengutronix.de>]

On Wed, Apr 14, 2021 at 03:54:43PM +0300, Antony Pavlov wrote:
> On Wed, 14 Apr 2021 13:20:44 +0200
> Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
> 
> > On 14.04.21 13:07, Antony Pavlov wrote:
> > > On Wed, 14 Apr 2021 11:54:27 +0200
> > > Sascha Hauer <sha@pengutronix.de> wrote:
> > > 
> > >> On Wed, Apr 14, 2021 at 08:54:22AM +0300, Antony Pavlov wrote:
> > >>> Hi Ahmad!
> > >>>
> > >>> Here is the iomem command output on erizo:
> > >>>
> > >>> barebox:/ iomem
> > >>> 0x00000000 - 0xffffffff (size 0x00000000) iomem
> > >>>   0x80000000 - 0x807fffff (size 0x00800000) ram0
> > >>>     0x804ffd00 - 0x805ffcff (size 0x00100000) malloc space
> > >>>     0x805ffd00 - 0x805fffe6 (size 0x000002e7) board data
> > >>>     0x80600000 - 0x80636b1f (size 0x00036b20) barebox
> > >>>     0x80636b20 - 0x8063ec9b (size 0x0000817c) barebox data
> > >>>     0x8063ec9c - 0x80643147 (size 0x000044ac) bss
> > >>>     0x807e0000 - 0x807fffff (size 0x00020000) stack
> > >>>   0x90000000 - 0x9000001f (size 0x00000020) 90000000.uart@90000000.of
> > >>>   0x91000000 - 0x91000003 (size 0x00000004) 91000000.gpio@91000000.of
> > >>>   0x91000004 - 0x91000007 (size 0x00000004) 91000000.gpio@91000000.of
> > >>>
> > >>> I see large unused region between bss and stack regions (>1600 Kbytes).
> > >>
> > >> That's normal. The compressed barebox knows the size of the uncompressed
> > >> barebox, but it doesn't know the size of the bss segment above it. For
> > >> that reason we have a very pessimistic estimate of:
> > >>
> > >> #define MAX_BSS_SIZE SZ_1M
> > >>
> > >> The barebox binary itself is then aligned to the previous 1MiB
> > >> boundary, so barebox usually starts at 2MiB below the end of SDRAM.
> > >> That's a bit wasteful for boards with very little memory like the erizo,
> > >> but that's how things are at the moment.
> > > 
> > > Can we make it configurable via Kconfig?
> > 
> > Or even better: Could we easily add to the piggy data the size of bss
> > it contains?
> > 
> 
> On MIPS we already have:
> 
>    bss_len = (unsigned long)&__bss_stop - (unsigned long)__bss_start;

When running in the decompressor that gives you the bss size of the
decompressor binary, but we need the bss size of barebox proper.

Sascha

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