arch/arc: Accommodate 16 KiB MMU pages

ARC processors are known for its configurability and one of those
configurable things is MMU page size which might be set to any
power of two from 4 KiB to 16 MiB, though in the Linux kernel we
only support 4, 8 and 16 KiB due to practical considerations.

And the most used setting is 8 KiB thus GNU LD assumes maximum
page size is 8 KiB by default and while this works for smaller
pages (it's OK to align segments by larger value it will be still
peoperly aligned) this breaks execution of user-space apps on HW
with larger pages because Elf sections might very well span across
allocated pages and thus make executable broken.

Simplest example:
------------------------------------>8-----------------------------------
$ arc-linux-gcc test.c
$ arc-linux-readelf --segments a.out

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
...
  LOAD           0x000000 0x00010000 0x00010000 0x003e8 0x003e8 R E 0x2000 <-- See
  LOAD           0x001f24 0x00013f24 0x00013f24 0x000f0 0x0010c RW  0x2000
------------------------------------>8-----------------------------------

Fortunately we may override default page size settings with "max-page-size"
linker option this way:
------------------------------------>8-----------------------------------
$ arc-linux-gcc test.c -Wl,-z,max-page-size=16384
$ arc-linux-readelf --segments a.out
Elf file type is EXEC (Executable file)
Entry point 0x102c4
There are 8 program headers, starting at offset 52

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
...
  LOAD           0x000000 0x00010000 0x00010000 0x003e8 0x003e8 R E 0x4000 <-- See
  LOAD           0x001f24 0x00015f24 0x00015f24 0x000f0 0x0010c RW  0x4000
------------------------------------>8-----------------------------------

Which we implement with that change.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
[yann.morin.1998@free.fr: fix comment: s/8196/8192/]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

diff --git a/arch/arch.mk.arc b/arch/arch.mk.arc
index 5fcffb7f4bfc3416dd66a8cbed253ab1b32cf3f2..9c04a85a8ddc1f4dbe2ec0d55f48ee518f51d4fb 100644 (file)
--- a/arch/arch.mk.arc
+++ b/arch/arch.mk.arc
@@ -1,4 +1,14 @@
+ifeq ($(BR2_arc),y)
+
 # -matomic is always required when the ARC core has the atomic extensions
-ifeq ($(BR2_arc)$(BR2_ARC_ATOMIC_EXT),yy)
+ifeq ($(BR2_ARC_ATOMIC_EXT),y)
 ARCH_TOOLCHAIN_WRAPPER_OPTS = -matomic
 endif
+
+# By default MAXPAGESIZE for ARC is 8192 so for larger MMU pages
+# it needs to be overridden.
+ifeq ($(BR2_ARC_PAGE_SIZE_16K),y)
+ARCH_TOOLCHAIN_WRAPPER_OPTS += -Wl,-z,max-page-size=16384
+endif
+
+endif