initramfs: fix initramfs size calculation

The size of a built-in initramfs is calculated in init/initramfs.c by
"__initramfs_end - __initramfs_start".  Those symbols are defined in the
linker script include/asm-generic/vmlinux.lds.h:

#define INIT_RAM_FS                                                     \
        . = ALIGN(PAGE_SIZE);                                           \
        VMLINUX_SYMBOL(__initramfs_start) = .;                          \
        *(.init.ramfs)                                                  \
        VMLINUX_SYMBOL(__initramfs_end) = .;

If the initramfs file has an odd number of bytes, the "__initramfs_end"
symbol points to an odd address, for example, the symbols in the
System.map might look like:

    0000000000572000 T __initramfs_start
    00000000005bcd05 T __initramfs_end	  <-- odd address

At least on s390 this causes a problem:

Certain s390 instructions, especially instructions for loading addresses
(larl) or branch addresses must be on even addresses.  The compiler loads
the symbol addresses with the "larl" instruction.  This instruction sets
the last bit to 0 and, therefore, for odd size files, the calculated size
is one byte less than it should be:

    0000000000540a9c <populate_rootfs>:
      540a9c:     eb cf f0 78 00 24       stmg    %r12,%r15,120(%r15),
      540aa2:     c0 10 00 01 8a af       larl    %r1,572000 <__initramfs_start>
      540aa8:     c0 c0 00 03 e1 2e       larl    %r12,5bcd04 <initramfs_end>
                                                  (Instead of  5bcd05)
      ...
      540abe:     1b c1                   sr      %r12,%r1

To fix the problem, this patch introduces the global variable
__initramfs_size, which is calculated in the "usr/initramfs_data.S" file.
The populate_rootfs() function can then use the start marker of the
.init.ramfs section and the value of __initramfs_size for loading the
initramfs.  Because the start marker and size is sufficient, the
__initramfs_end symbol is no longer needed and is removed.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Acked-by: "H. Peter Anvin" <hpa@zytor.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

1 files changed, 11 insertions, 5 deletions

diff --git a/usr/initramfs_data.S b/usr/initramfs_data.S
index 49a545fea120..b9efed5e35cc 100644
--- a/usr/initramfs_data.S
+++ b/usr/initramfs_data.S
@@ -11,11 +11,7 @@
   -T initramfs_data.scr initramfs_data.cpio.gz -o initramfs_data.o
    ld -m elf_i386  -r -o built-in.o initramfs_data.o
 
-  initramfs_data.scr looks like this:
-SECTIONS
-{
-       .init.ramfs : { *(.data) }
-}
+  For including the .init.ramfs sections, see include/asm-generic/vmlinux.lds.
 
   The above example is for i386 - the parameters vary from architectures.
   Eventually look up LDFLAGS_BLOB in an older version of the
@@ -28,4 +24,14 @@ SECTIONS
 #include <linux/stringify.h>
 
 .section .init.ramfs,"a"
+__irf_start:
 .incbin __stringify(INITRAMFS_IMAGE)
+__irf_end:
+.section .init.ramfs.info,"a"
+.globl __initramfs_size
+__initramfs_size:
+#ifdef CONFIG_32BIT
+        .long __irf_end - __irf_start
+#else
+        .quad __irf_end - __irf_start
+#endif