coreboot/payloads/libpayload
Gabe Black ca88f39c21 libpayload: arm: Pass the coreboot table location to the payload.
To find the coreboot tables, the payload has historically searched for their
signature in a predefined region of memory. This is a little clumsy on x86,
but it works because you can assume certain regions are RAM. Also, there are
areas which are set aside for the firmware by convention. On x86 there's a
forwarding entry which goes in one of those fairly small conventional areas
and which points to the CBMEM area at the end of memory.

On ARM there aren't areas like that, so we've left out the forwarding entry and
gone directly to CBMEM. RAM may not start at the beginning of the address space
or go to its end, and that means there isn't really anywhere fixed you can put
the coreboot tables. That's meant that libpayload has to be configured on a
per board basis to know where to look for CBMEM.

Now that we have boards that don't have fixed amounts of memory, the location
of the end of RAM isn't fixed even on a per board level which means even that
workaround will no longer cut it.

This change makes coreboot pass the location of the coreboot tables to
libpayload using r0, the first argument register. That means we'll be able to
find them no matter where CBMEM is, and we can get rid of the per board search
ranges.

We can extend this mechanism to x86 as well, but there may be more
complications and it's less necessary there. It would be a good thing to do
eventually though.

BUG=None
TEST=Built and booted on nyan. Changed the size of memory and saw that the
payload could still find the coreboot tables where before it couldn't. Built
for pit, snow, and big.
BRANCH=None

Change-Id: I7218afd999da1662b0db8172fd8125670ceac471
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/185572
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
2014-02-11 05:30:59 +00:00
..
arch libpayload: arm: Pass the coreboot table location to the payload. 2014-02-11 05:30:59 +00:00
bin ARM: Generalize armv7 as arm. 2013-10-02 09:18:44 +00:00
configs libpayload: arm: Pass the coreboot table location to the payload. 2014-02-11 05:30:59 +00:00
crypto libpayload: Change CONFIG_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
curses libpayload: Change CONFIG_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
drivers libpayload: find source of input characters 2014-01-19 04:15:03 +00:00
include arm: Put assembly functions into separate sections 2014-01-29 21:33:41 +00:00
libc libpayload: find source of input characters 2014-01-19 04:15:03 +00:00
libcbfs cbfs: Fix overwalk on file scan 2013-08-19 17:29:35 -07:00
liblzma libpayload: Make lzma truncation non-fatal. 2013-08-19 19:04:35 -07:00
libpci libpayload: minor cleanups 2012-04-04 00:40:31 +02:00
sample fix compilation of hello.elf example payload. 2010-08-28 23:23:47 +00:00
tests libpayload: Change CONFIG_X86_SERIAL_CONSOLE to CONFIG_8250_SERIAL_CONSOLE 2013-09-27 14:05:53 +00:00
util Set check-lxdialog.sh mode properly 2013-10-22 21:41:24 +00:00
Config.in ARM: Generalize armv7 as arm. 2013-10-02 09:18:44 +00:00
Doxyfile Run doxygen -u on doxygen configuration files 2010-06-28 10:40:38 +00:00
LICENSES Since some people disapprove of white space cleanups mixed in regular commits 2010-04-27 06:56:47 +00:00
Makefile ARM: Generalize armv7 as arm. 2013-10-02 09:18:44 +00:00
Makefile.inc ARM: Generalize armv7 as arm. 2013-10-02 09:18:44 +00:00
README libpayload, superiotool: README: Prepend coreboot/ to path of change directory line 2013-04-04 17:22:15 +02:00

-------------------------------------------------------------------------------
libpayload README
-------------------------------------------------------------------------------

libpayload is a minimal library to support standalone payloads
that can be booted with firmware like coreboot. It handles the setup
code, and provides common C library symbols such as malloc() and printf().

Note: This is _not_ a standard library for use with an operating system,
rather it's only useful for coreboot payload development!
See http://coreboot.org for details on coreboot.


Installation
------------

 $ git clone http://review.coreboot.org/p/coreboot.git

 $ cd coreboot/payloads/libpayload

 $ make menuconfig

 $ make

 $ sudo make install (optional, will install into /opt per default)

As libpayload is for 32bit x86 systems only, you might have to install the
32bit libgcc version, otherwise your payloads will fail to compile.
On Debian systems you'd do 'apt-get install gcc-multilib' for example.


Usage
-----

Here's an example of a very simple payload (hello.c) and how to build it:

 #include <libpayload.h>

 int main(void)
 {
     printf("Hello, world!\n");
     return 0;
 }

Building the payload using the 'lpgcc' compiler wrapper:

 $ lpgcc -o hello.elf hello.c

Please see the sample/ directory for details.


Website and Mailing List
------------------------

The main website is http://www.coreboot.org/Libpayload.

For additional information, patches, and discussions, please join the
coreboot mailing list at http://coreboot.org/Mailinglist, where most
libpayload developers are subscribed.


Copyright and License
---------------------

See LICENSES.