ARM: 6750/1: improvements to compressed/head.S

In the case of a conflict between the memory used by the compressed
kernel with its decompressor code and the memory used for the
decompressed kernel, we currently store the later after the former and
relocate it afterwards.

This would be more efficient to do this the other way around i.e.
relocate the compressed data up front instead, resulting in a smaller
copy.  That also has the advantage of making the code smaller and more
straight forward.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 110 insertions, 129 deletions

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 920f4dbd4883..39859216af00 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -174,9 +174,7 @@ not_angel:
                  */
 
                 .text
-                adr     r0, LC0
-                ldmia   r0, {r1, r2, r3, r5, r6, r11, ip}
-                ldr     sp, [r0, #28]
+
 #ifdef CONFIG_AUTO_ZRELADDR
                 @ determine final kernel image address
                 mov     r4, pc
@@ -185,35 +183,108 @@ not_angel:
 #else
                 ldr     r4, =zreladdr
 #endif
-                subs    r0, r0, r1              @ calculate the delta offset
 
-                                                @ if delta is zero, we are
-                beq     not_relocated           @ running at the address we
-                                                @ were linked at.
+                bl      cache_on
+
+restart:        adr     r0, LC0
+                ldmia   r0, {r1, r2, r3, r5, r6, r9, r11, r12}
+                ldr     sp, [r0, #32]
+
+                /*
+                 * We might be running at a different address.  We need
+                 * to fix up various pointers.
+                 */
+                sub     r0, r0, r1              @ calculate the delta offset
+                add     r5, r5, r0              @ _start
+                add     r6, r6, r0              @ _edata
 
+#ifndef CONFIG_ZBOOT_ROM
+                /* malloc space is above the relocated stack (64k max) */
+                add     sp, sp, r0
+                add     r10, sp, #0x10000
+#else
                 /*
-                 * We're running at a different address.  We need to fix
-                 * up various pointers:
-                 *   r5 - zImage base address (_start)
-                 *   r6 - size of decompressed image
-                 *   r11 - GOT start
-                 *   ip - GOT end
+                 * With ZBOOT_ROM the bss/stack is non relocatable,
+                 * but someone could still run this code from RAM,
+                 * in which case our reference is _edata.
                  */
-                add     r5, r5, r0
+                mov     r10, r6
+#endif
+
+/*
+ * Check to see if we will overwrite ourselves.
+ *   r4  = final kernel address
+ *   r5  = start of this image
+ *   r9  = size of decompressed image
+ *   r10 = end of this image, including  bss/stack/malloc space if non XIP
+ * We basically want:
+ *   r4 >= r10 -> OK
+ *   r4 + image length <= r5 -> OK
+ */
+                cmp     r4, r10
+                bhs     wont_overwrite
+                add     r10, r4, r9
+                cmp     r10, r5
+                bls     wont_overwrite
+
+/*
+ * Relocate ourselves past the end of the decompressed kernel.
+ *   r5  = start of this image
+ *   r6  = _edata
+ *   r10 = end of the decompressed kernel
+ * Because we always copy ahead, we need to do it from the end and go
+ * backward in case the source and destination overlap.
+ */
+                /* Round up to next 256-byte boundary. */
+                add     r10, r10, #256
+                bic     r10, r10, #255
+
+                sub     r9, r6, r5              @ size to copy
+                add     r9, r9, #31             @ rounded up to a multiple
+                bic     r9, r9, #31             @ ... of 32 bytes
+                add     r6, r9, r5
+                add     r9, r9, r10
+
+1:              ldmdb   r6!, {r0 - r3, r10 - r12, lr}
+                cmp     r6, r5
+                stmdb   r9!, {r0 - r3, r10 - r12, lr}
+                bhi     1b
+
+                /* Preserve offset to relocated code. */
+                sub     r6, r9, r6
+
+                bl      cache_clean_flush
+
+                adr     r0, BSYM(restart)
+                add     r0, r0, r6
+                mov     pc, r0
+
+wont_overwrite:
+/*
+ * If delta is zero, we are running at the address we were linked at.
+ *   r0  = delta
+ *   r2  = BSS start
+ *   r3  = BSS end
+ *   r4  = kernel execution address
+ *   r7  = architecture ID
+ *   r8  = atags pointer
+ *   r11 = GOT start
+ *   r12 = GOT end
+ *   sp  = stack pointer
+ */
+                teq     r0, #0
+                beq     not_relocated
                 add     r11, r11, r0
-                add     ip, ip, r0
+                add     r12, r12, r0
 
 #ifndef CONFIG_ZBOOT_ROM
                 /*
                  * If we're running fully PIC === CONFIG_ZBOOT_ROM = n,
                  * we need to fix up pointers into the BSS region.
-                 *   r2 - BSS start
-                 *   r3 - BSS end
-                 *   sp - stack pointer
+                 * Note that the stack pointer has already been fixed up.
                  */
                 add     r2, r2, r0
                 add     r3, r3, r0
-                add     sp, sp, r0
 
                 /*
                  * Relocate all entries in the GOT table.
@@ -221,7 +292,7 @@ not_angel:
 1:              ldr     r1, [r11, #0]           @ relocate entries in the GOT
                 add     r1, r1, r0              @ table.  This fixes up the
                 str     r1, [r11], #4           @ C references.
-                cmp     r11, ip
+                cmp     r11, r12
                 blo     1b
 #else
 
@@ -234,7 +305,7 @@ not_angel:
                 cmphs   r3, r1                  @ _end < entry
                 addlo   r1, r1, r0              @ table.  This fixes up the
                 str     r1, [r11], #4           @ C references.
-                cmp     r11, ip
+                cmp     r11, r12
                 blo     1b
 #endif
 
@@ -246,76 +317,24 @@ not_relocated:	mov	r0, #0
                 cmp     r2, r3
                 blo     1b
 
-                /*
-                 * The C runtime environment should now be setup
-                 * sufficiently.  Turn the cache on, set up some
-                 * pointers, and start decompressing.
-                 */
-                bl      cache_on
-
-                mov     r1, sp                  @ malloc space above stack
-                add     r2, sp, #0x10000        @ 64k max
-
 /*
- * Check to see if we will overwrite ourselves.
- *   r4 = final kernel address
- *   r5 = start of this image
- *   r6 = size of decompressed image
- *   r2 = end of malloc space (and therefore this image)
- * We basically want:
- *   r4 >= r2 -> OK
- *   r4 + image length <= r5 -> OK
+ * The C runtime environment should now be setup sufficiently.
+ * Set up some pointers, and start decompressing.
+ *   r4  = kernel execution address
+ *   r7  = architecture ID
+ *   r8  = atags pointer
  */
-                cmp     r4, r2
-                bhs     wont_overwrite
-                add     r0, r4, r6
-                cmp     r0, r5
-                bls     wont_overwrite
-
-                mov     r5, r2                  @ decompress after malloc space
-                mov     r0, r5
+                mov     r0, r4
+                mov     r1, sp                  @ malloc space above stack
+                add     r2, sp, #0x10000        @ 64k max
                 mov     r3, r7
                 bl      decompress_kernel
-
-                add     r0, r0, #127 + 128      @ alignment + stack
-                bic     r0, r0, #127            @ align the kernel length
-/*
- * r0     = decompressed kernel length
- * r1-r3  = unused
- * r4     = kernel execution address
- * r5     = decompressed kernel start
- * r7     = architecture ID
- * r8     = atags pointer
- * r9-r12,r14 = corrupted
- */
-                add     r1, r5, r0              @ end of decompressed kernel
-                adr     r2, reloc_start
-                ldr     r3, LC1
-                add     r3, r2, r3
-1:              ldmia   r2!, {r9 - r12, r14}    @ copy relocation code
-                stmia   r1!, {r9 - r12, r14}
-                ldmia   r2!, {r9 - r12, r14}
-                stmia   r1!, {r9 - r12, r14}
-                cmp     r2, r3
-                blo     1b
-                mov     sp, r1
-                add     sp, sp, #128            @ relocate the stack
-
                 bl      cache_clean_flush
- ARM(           add     pc, r5, r0              ) @ call relocation code
- THUMB(         add     r12, r5, r0             )
- THUMB(         mov     pc, r12                 ) @ call relocation code
-
-/*
- * We're not in danger of overwriting ourselves.  Do this the simple way.
- *
- * r4     = kernel execution address
- * r7     = architecture ID
- */
-wont_overwrite: mov     r0, r4
-                mov     r3, r7
-                bl      decompress_kernel
-                b       call_kernel
+                bl      cache_off
+                mov     r0, #0                  @ must be zero
+                mov     r1, r7                  @ restore architecture number
+                mov     r2, r8                  @ restore atags pointer
+                mov     pc, r4                  @ call kernel
 
                 .align  2
                 .type   LC0, #object
@@ -323,11 +342,11 @@ LC0:		.word	LC0			@ r1
                 .word   __bss_start             @ r2
                 .word   _end                    @ r3
                 .word   _start                  @ r5
-                .word   _image_size             @ r6
+                .word   _edata                  @ r6
+                .word   _image_size             @ r9
                 .word   _got_start              @ r11
                 .word   _got_end                @ ip
                 .word   user_stack_end          @ sp
-LC1:            .word   reloc_end - reloc_start
                 .size   LC0, . - LC0
 
 #ifdef CONFIG_ARCH_RPC
@@ -353,7 +372,7 @@ params:		ldr	r0, =0x10000100		@ params_phys for RPC
  * On exit,
  *  r0, r1, r2, r3, r9, r10, r12 corrupted
  * This routine must preserve:
- *  r4, r5, r6, r7, r8
+ *  r4, r7, r8
  */
                 .align  5
 cache_on:       mov     r3, #8                  @ cache_on function
@@ -551,43 +570,6 @@ __common_mmu_cache_on:
 #endif
 
 /*
- * All code following this line is relocatable.  It is relocated by
- * the above code to the end of the decompressed kernel image and
- * executed there.  During this time, we have no stacks.
- *
- * r0     = decompressed kernel length
- * r1-r3  = unused
- * r4     = kernel execution address
- * r5     = decompressed kernel start
- * r7     = architecture ID
- * r8     = atags pointer
- * r9-r12,r14 = corrupted
- */
-                .align  5
-reloc_start:    add     r9, r5, r0
-                sub     r9, r9, #128            @ do not copy the stack
-                debug_reloc_start
-                mov     r1, r4
-1:
-                .rept   4
-                ldmia   r5!, {r0, r2, r3, r10 - r12, r14}       @ relocate kernel
-                stmia   r1!, {r0, r2, r3, r10 - r12, r14}
-                .endr
-
-                cmp     r5, r9
-                blo     1b
-                mov     sp, r1
-                add     sp, sp, #128            @ relocate the stack
-                debug_reloc_end
-
-call_kernel:    bl      cache_clean_flush
-                bl      cache_off
-                mov     r0, #0                  @ must be zero
-                mov     r1, r7                  @ restore architecture number
-                mov     r2, r8                  @ restore atags pointer
-                mov     pc, r4                  @ call kernel
-
-/*
  * Here follow the relocatable cache support functions for the
  * various processors.  This is a generic hook for locating an
  * entry and jumping to an instruction at the specified offset
@@ -791,7 +773,7 @@ proc_types:
  * On exit,
  *  r0, r1, r2, r3, r9, r12 corrupted
  * This routine must preserve:
- *  r4, r6, r7
+ *  r4, r7, r8
  */
                 .align  5
 cache_off:      mov     r3, #12                 @ cache_off function
@@ -866,7 +848,7 @@ __armv3_mmu_cache_off:
  * On exit,
  *  r1, r2, r3, r9, r10, r11, r12 corrupted
  * This routine must preserve:
- *  r0, r4, r5, r6, r7
+ *  r4, r6, r7, r8
  */
                 .align  5
 cache_clean_flush:
@@ -1088,7 +1070,6 @@ memdump:	mov	r12, r0
 #endif
 
                 .ltorg
-reloc_end:
 
                 .align
                 .section ".stack", "aw", %nobits