Subject: N900 v3.19-rc5 arm atags_to_fdt.c is broken

From: [email-masked] (Pavel Machek)
Date: Tue, 27 Jan 2015 14:37:39 +0100

> > > I would say, problem is because omap3-n900 binary DT is too large
> 
> I agree.
> 
> > OK if that's the case, then your patch makes sense to me. It also
> > seems we can have the temporary stack be larger than the initial
> > stack just for atags_to_fdt.
> 
> The stack size isn't the issue, but rather its location.  We need to 
> position it away from the DT data.  The DT size is known and we could 
> use that, plus some room for the insertion of new data coming from the
> ATAG conversion.
> 
> Something like the following would be a more robust solution:

Tested-by: Pavel Machek <[email-masked]>

(Note, that in 3.19 dts for n900 got too big, so we are actually
triggering old bugs. That means that this is a regression fix, and
should go in ASAP).

> 
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 68be901759..89718de9dd 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -263,16 +263,37 @@ restart:	adr	r0, LC0
>  		 * OK... Let's do some funky business here.
>  		 * If we do have a DTB appended to zImage, and we do have
>  		 * an ATAG list around, we want the later to be translated
> -		 * and folded into the former here.  To be on the safe side,
> -		 * let's temporarily move  the stack away into the malloc
> -		 * area.  No GOT fixup has occurred yet, but none of the
> -		 * code we're about to call uses any global variable.
> +		 * and folded into the former here. No GOT fixup has occurred
> +		 * yet, but none of the code we're about to call uses any
> +		 * global variable.
>  		*/
> -		add	sp, sp, #0x10000
> +
> +		/* Get the initial DTB size */
> +		ldr	r5, [r6, #4]
> +#ifndef __ARMEB__
> +		/* convert to little endian */
> +		eor	r1, r5, r5, ror #16
> +		bic	r1, r1, #0x00ff0000
> +		mov	r5, r5, ror #8
> +		eor	r5, r5, r1, lsr #8
> +#endif
> +		/* 50% DTB growth should be good enough */
> +		add	r5, r5, r5, lsr #1
> +		/* preserve 64-bit alignment */
> +		add	r5, r5, #7
> +		bic	r5, r5, #7
> +		/* clamp to 32KB min and 1MB max */
> +		movs	r1, r5, lsr #15
> +		moveq	r5, #(1 << 15)
> +		movs	r1, r5, lsr #20
> +		movne	r5, #(1 << 20)
> +
> +		/* Temporarily relocate the stack past the DTB work space */
> +		add	sp, sp, r5
>  		stmfd	sp!, {r0-r3, ip, lr}
>  		mov	r0, r8
>  		mov	r1, r6
> -		sub	r2, sp, r6
> +		mov	r2, r5
>  		bl	atags_to_fdt
>  
>  		/*
> @@ -285,11 +306,11 @@ restart:	adr	r0, LC0
>  		bic	r0, r0, #1
>  		add	r0, r0, #0x100
>  		mov	r1, r6
> -		sub	r2, sp, r6
> +		mov	r2, r5
>  		bleq	atags_to_fdt
>  
>  		ldmfd	sp!, {r0-r3, ip, lr}
> -		sub	sp, sp, #0x10000
> +		sub	sp, sp, r5
>  #endif
>  
>  		mov	r8, r6			@ use the appended device tree
> @@ -306,7 +327,7 @@ restart:	adr	r0, LC0
>  		subs	r1, r5, r1
>  		addhi	r9, r9, r1
>  
> -		/* Get the dtb's size */
> +		/* Get the current DTB size */
>  		ldr	r5, [r6, #4]
>  #ifndef __ARMEB__
>  		/* convert r5 (dtb size) to little endian */

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