Starting v4.13, Linux always uses thin archive instead of relocatable
ELF to combine builtin objects.

The thin archive is basically a text file that only contains paths to
object files.

As Linux commit 98ced886dd79 mentioned, this has a lot of benefits:

 - save disk space for builds

 - speed-up building a little

 - fix some issues when liking a giant executable (for example,
   allyesconfig on ARM Linux)

 - work better with dead code elimination

The last one is important for barebox because pbl highly relies on the
dead code elimination (-f{function,data}-sections and --gc-sections)
dropping symbols that are unreachable from the linker's entry point.
The dead code elimination does not work if the same symbol names are
used in the pevious incremental link mechanism because the same name
symbols all go into the same section.

Commit a83c97f2a406 ("ARM: socfpga: generate smaller images when
multiple boards are selected") worked around it by giving a dedicate
section to each of the same name symbols. This workaround can go away.

built-in.o was renamed to built-in.a since it is now an archive.
built-in-pbl.o was renamed to built-in.pbl.a for consistency.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

In old days, Linux also used to use well-known variables such CFLAGS,
CPPFLAGS, etc.

They were prefixed with KBUILD_ presumably for preventing users from
overriding them accidentally.

Rename as follows:
  CFLAGS          ->  KBUILD_CFLAGS
  AFLAGS          ->  KBUILD_AFLAGS
  CPPFLAGS        ->  KBUILD_CPPFLAGS
  LDFLAGS         ->  KBUILD_LDFLAGS
  HOSTCFLAGS      ->  KBUILD_HOSTCFLAGS
  HOSTCXXFLAGS    ->  KBUILD_HOSTCXXFLAGS
  HOSTLDFLAGS     ->  KBUILD_HOSTLDFLAGS
  HOST_LOADLIBES  ->  KBUILD_HOSTLDLIBS

HOSTCFLAGS, HOSTCXXFLAGS, HOSTLDFLAGS, HOSTLDLIBS are re-used to allow
users to pass-in additional flags to the host compiler.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

'export barebox-pbl-common' does not work reliably because hyphens
are disallowed in shell variables.

This caused a problem in Linux in the past. See Linux commit 2bfbe7881ee0
("kbuild: Do not use hyphen in exported variable name").

The same problem occurs when you build barebox with O= and the directory
path to the source tree contains a shell special character like '~'.

The maintainer of GNU Make stated that there is no consistent way to
export variables that do not meet the shell's naming criteria.
(https://savannah.gnu.org/bugs/?55719)

Consequently, you cannot use hyphens in exported variables.

Rename barebox-pbl-common to BAREBOX_PBL_OBJS.

I named it after KBUILD_VMLINUX_OBJS in the Linux top Makefile.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Also ignore piggy.shipped binary (CONFIG_IMAGE_COMPRESSION_NONE=y).

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Make 'check_file_size' more flexible by not hardcoding the file whose
size is going to be checked to '$@'. This way it is possible to use
this subroutine to check the size of files other than the target of
the rule.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

This patch is based on ARM pbl support and allows
creating a pre-bootloader binary for compressed image.

For different MIPS SoCs (or even for different boards based
 on the same SoC) the operations carried on in start-pbl.S
can be very different. The additional constraints can be imposed
on the size of the boot code or the special magic labels in
the beginning of the boot code; In some cases it could be
necessary to show CPU is alive as early as possible
(transmit a char via UART or blink a LED).
So the demands for pbl start operation can be very different.

E.g. malta board store boot code at the NOR flash mapped
to the MIPS power-on address (0xbfc00000); it is the most
simple case: we need just copy pbl image from direct-mapped
flash to RAM and jump there.

The XBurst-powered boards store boot code in the beginning
of a NAND flash or in the beginning of SD/MMC card.
In this case we must use simple and short NAND or SD/MMC access
routines to copy pbl image to RAM.

To meet so different demands a simple technique is selected:

* MIPS pbl entry point located in file arch/mips/boot/start-pbl.S.

* MIPS pbl code (see start-pbl.S) assumes that every pbl-enabled
board has a arch/mips/boards/<BOARD>/include/board/board_pbl_start.h
header file. This file must contain definition of
the board_pbl_start macro. This macro is used as start of pbl image;

* the most popular asm routines (stack setup, relocation to link
address, NS16550 initialization (WIP) and so on) are containt
in the arch/mips/include/asm/pbl_macros.h header file.
So board pbl macro can use it if necessary.
It is possible to create similar headers with macros for each
specific SoC; so even if we have many different boards based
on the same SoC the board_pbl_start macro for every board
can be short and clear.

* after board-specific initialization the stack pointer
is initialized and pbl C code is started.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>