Merge tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm

Pull ARM updates from Russell King:

 - fix various clang build and cppcheck issues

 - switch ARM to use new common outgoing-CPU-notification code

 - add some additional explanation about the boot code

 - kbuild "make clean" fixes

 - get rid of another "(____ptrval____)", this time for the VDSO code

 - avoid treating cache maintenance faults as a write

 - add a frame pointer unwinder implementation for clang

 - add EDAC support for Aurora L2 cache

 - improve robustness of adjust_lowmem_bounds() finding the bounds of
   lowmem.

 - add reset control for AMBA primecell devices

* tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm: (24 commits)
  ARM: 8906/1: drivers/amba: add reset control to amba bus probe
  ARM: 8905/1: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
  ARM: 8904/1: skip nomap memblocks while finding the lowmem/highmem boundary
  ARM: 8903/1: ensure that usable memory in bank 0 starts from a PMD-aligned address
  ARM: 8891/1: EDAC: armada_xp: Add support for more SoCs
  ARM: 8888/1: EDAC: Add driver for the Marvell Armada XP SDRAM and L2 cache ECC
  ARM: 8892/1: EDAC: Add missing debugfs_create_x32 wrapper
  ARM: 8890/1: l2x0: add marvell,ecc-enable property for aurora
  ARM: 8889/1: dt-bindings: document marvell,ecc-enable binding
  ARM: 8886/1: l2x0: support parity-enable/disable on aurora
  ARM: 8885/1: aurora-l2: add defines for parity and ECC registers
  ARM: 8887/1: aurora-l2: add prefix to MAX_RANGE_SIZE
  ARM: 8902/1: l2c: move cache-aurora-l2.h to asm/hardware
  ARM: 8900/1: UNWINDER_FRAME_POINTER implementation for Clang
  ARM: 8898/1: mm: Don't treat faults reported from cache maintenance as writes
  ARM: 8896/1: VDSO: Don't leak kernel addresses
  ARM: 8895/1: visit mach-* and plat-* directories when cleaning
  ARM: 8894/1: boot: Replace open-coded nop with macro
  ARM: 8893/1: boot: Explain the 8 nops
  ARM: 8876/1: fix O= building with CONFIG_FPE_FASTFPE
  ...

1 files changed, 13 insertions, 1 deletions

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index e59d14679fb0..93dffed0ac6e 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -153,11 +153,23 @@
  AR_CLASS(	.arm	)
 start:
 		.type	start,#function
+		/*
+		 * These 7 nops along with the 1 nop immediately below for
+		 * !THUMB2 form 8 nops that make the compressed kernel bootable
+		 * on legacy ARM systems that were assuming the kernel in a.out
+		 * binary format. The boot loaders on these systems would
+		 * jump 32 bytes into the image to skip the a.out header.
+		 * with these 8 nops filling exactly 32 bytes, things still
+		 * work as expected on these legacy systems. Thumb2 mode keeps
+		 * 7 of the nops as it turns out that some boot loaders
+		 * were patching the initial instructions of the kernel, i.e
+		 * had started to exploit this "patch area".
+		 */
 		.rept	7
 		__nop
 		.endr
 #ifndef CONFIG_THUMB2_KERNEL
-		mov	r0, r0
+		__nop
 #else
  AR_CLASS(	sub	pc, pc, #3	)	@ A/R: switch to Thumb2 mode
   M_CLASS(	nop.w			)	@ M: already in Thumb2 mode