Re: [PATCH v1] MIPS: remove .bss to __rel_start overlay

[Antony Pavlov <antonynpavlov@gmail.com>]

On Tue, 28 Jan 2020 10:28:32 +0100
Oleksij Rempel <o.rempel@pengutronix.de> wrote:

Hi!

Looks like this patch has some undocummented side effects
(or in other words, it makes undocummented fixups).

I have tested this patch on qemu-malta with current master,
ee8960aec018df2de ("ARM: imx6: properly check for IPU presence").
It works fine: memtest works, iomem output looks good.

But the patch fixes several issues and commit message does not contain
any information about it.

I rebuild current master with qemu-malta_defconfig and MMU enabled.

I used this qemu cmdline to enable qemu monitor:

qemu-system-mips -nodefaults -M malta -m 256 -nographic -bios barebox-flash-image
   -net user -net nic,model=rtl8139 -serial mon:stdio

With '-serial mon:stdio' one can invoke qemu monitor with "ctrl-a c" keypress sequence.

So I tried 'info registers' qemu monitor command after barebox startup:

Hit any to stop autoboot:    3
barebox@qemu malta:/ 
barebox@qemu malta:/ 
barebox@qemu malta:/ iomem
0x00000000 - 0xffffffff (size 0x00000000) iomem
  0x180003f8 - 0x180003ff (size 0x00000008) 180003f8.serial@180003f8.of
  0x1e000000 - 0x1e3fffff (size 0x00400000) 1e000000.flash@1e000000.of
  0x1f000900 - 0x1f00093f (size 0x00000040) 1f000900.serial@1f000900.of
  0x1f000b00 - 0x1f000b1f (size 0x00000020) 1f000b00.gpio@1f000b00.of
  0x80000000 - 0x8fffffff (size 0x10000000) kseg0_ram0
barebox@qemu malta:/ QEMU 4.2.0 monitor - type 'help' for more information
(qemu) info registers 
pc=0xa081232c HI=0x00000026 LO=0x20000000 ds 0090 a081232c 1
GPR00: r0 00000000 at 00000000 v0 b80003f8 v1 00000000
GPR04: a0 a0408668 a1 b80003fd a2 b80003f8 a3 ffffffff
GPR08: t0 00000001 t1 00000000 t2 0000005a t3 00000023
GPR12: t4 00000000 t5 00010000 t6 00000040 t7 00000010
GPR16: s0 a0408668 s1 a085cd20 s2 a0860000 s3 a0860000
GPR20: s4 a0860000 s5 00000400 s6 a08613c0 s7 00000001
GPR24: t8 00000008 t9 a0812340 k0 00400000 k1 fffffffa
GPR28: gp 00000000 sp 8fb8fd10 s8 ffffffff ra a0812420
CP0 Status  0x00000000 Cause   0x00000400 EPC    0x00000000
    Config0 0x80008482 Config1 0x9e190c8f LLAddr 0x0000000000000000
    Config2 0x80000000 Config3 0x00000000
    Config4 0x00000000 Config5 0x00000000
(qemu) quit

So I see several issues in current master at once:

  * 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.

Your patch fixes all these symptoms at ones however the commit message
says nothing about them.

> .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.
> 
> 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.
> 
> Fixes: 1e5aef61fc6a444 ("MIPS: reloc: init bss and cpu")
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> ---
>  arch/mips/lib/barebox.lds.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/lib/barebox.lds.S b/arch/mips/lib/barebox.lds.S
> index 693a778980..c954df41f3 100644
> --- a/arch/mips/lib/barebox.lds.S
> +++ b/arch/mips/lib/barebox.lds.S
> @@ -59,7 +59,7 @@ SECTIONS
>  
>  	_end = .;
>  
> -	.bss __rel_start (OVERLAY) : {
> +	.bss : {
>  		__bss_start = .;
>  		*(.sbss.*)
>  		*(.bss.*)
> -- 
> 2.25.0
> 


-- 
Best regards,
  Antony Pavlov

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