coreboot/payloads/libpayload
Julius Werner 702dc50f1d libpayload: ehci: Cache management is hard, let's go copying...
It turns out that my previous commit to make the EHCI stack cache aware
on ARM devices wasn't quite correct, and the problem is actually much
trickier than I thought. After having some fun with more weird transfer
problems that appear/disappear based on stack alignment, this is my
current worst-case threat model that any cache managing implementation
would need to handle correctly:

Some upper layer calls ehci_bulk() with a transfer buffer on its stack.
Due to stack alignment, it happens to start just at the top of a cache
line, so up to 64 - 4 bytes of ehci_bulk's stack will share that line.
ehci_bulk() calls dcache_clean() and initializes the USB transfer.
Between that point and the call to dcache_invalidate() at the end of
ehci_bulk(), any access to the stack variables in that cache line (even
a speculative prefetch) will refetch the line into the cache. Afterwards
any other access to a random memory location that just happens to get
aliased to the same cache line may evict it again, causing the processor
to write out stale data to the transfer buffer and possibly overwrite
data that has already been received over USB.

In short, any dcache_clean/dcache_invalidate-based implementation that
preserves correctness while allowing any arbitrary (non cache-aligned)
memory location as a transfer buffer is presumed to be impossible.
Instead, this patch causes all transfer data to be copied to/from a
cache-coherent bounce buffer. It will still transfer directly if the
supplied buffer is already cache-coherent, which can be used by callers
to optimize their transfers (and is true by default on x86).

CQ-DEPEND=CL:169170
BUG=chrome-os-partner:21969
TEST=Make sure Snow still boots from the USB 2.0 port.

Change-Id: I112908410bdbc8ca028d44f2f5d388c529f8057f
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/169231
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
2013-09-14 01:31:18 +00:00
..
arch arm: libpayload: Make cache invalidation take pointers instead of integers 2013-08-29 22:48:54 +00:00
bin libpayload: Change CONFIG_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
configs beltino: add libpayload config file 2013-09-13 22:18:56 +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: ehci: Cache management is hard, let's go copying... 2013-09-14 01:31:18 +00:00
include libpayload: ehci: Cache management is hard, let's go copying... 2013-09-14 01:31:18 +00:00
libc libpayload: ehci: Cache management is hard, let's go copying... 2013-09-14 01:31:18 +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_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
util libpayload: Change CONFIG_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
Config.in libpayload: Drop PowerPC architecture 2013-06-13 15:50:38 -07:00
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 libpayload: Change CONFIG_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
Makefile.inc libpayload: Change CONFIG_* to CONFIG_LP_* in the kconfig. 2013-08-14 17:05:33 -07:00
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.