ARM: 8294/1: ATAG_DTB_COMPAT: remove the DT workspace's hardcoded 64KB size

There is currently a hardcoded limit of 64KB for the DTB to live in and
be extended with ATAG info.  Some DTBs have outgrown that limit:

$ du -b arch/arm/boot/dts/omap3-n900.dtb
70212   arch/arm/boot/dts/omap3-n900.dtb

Furthermore, the actual size passed to atags_to_fdt() included the stack
size which is obviously wrong.

The initial DTB size is known, so use it to size the allocated workspace
with a 50% growth assumption and relocate the temporary stack above that.
This is also clamped to 32KB min / 1MB max for robustness against bad
DTB data.

Reported-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 68be9017593df10f235ca228a6837aaa11f5c818..132c70e2d2f11cfb4e655ddcb05931be5bd03498 100644 (file)
--- 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 */
+               cmp     r5, #(1 << 15)
+               movlo   r5, #(1 << 15)
+               cmp     r5, #(1 << 20)
+               movhi   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 */