2fe505bd9a
The console output driver framework in libpayload is currently built on
the putchar primitive, meaning that every driver's function gets called
one character at a time. This becomes an issue when we add drivers that
could output multiple characters at a time, but have a high constant
overhead per invocation (such as the planned GDB stub, which needs to
wrap a special frame around output strings and wait for an
acknowledgement from the server).
This patch adds a new 'write' function pointer to the
console_output_driver structure as an alternative to 'putchar'. Output
drivers need to provide at least one of the two ('write' is preferred if
available). The CBMEM console driver is ported as a proof of concept
(since it's our most performace-critical driver and should in theory
benefit the most from less function pointer invocations, although it's
probably still negligible compared to the big sprawling mess that is
printf()).
Even with this fix, the problem remains that printf() was written with
the putchar primitive in mind. Even though normal text already contains
an optimization to allow multiple characters at a time, almost all
formatting directives cause their output (including things like
padding whitespace) to be putchar()ed one character at a time.
Therefore, this patch reworks parts of the output code (especially
number printing) to all but remove that inefficiency (directives still
invoke an extra write() call, but at least not one per character). Since
I'm touching printf() core code anyway, I also tried to salvage what I
could from that weird, broken "return negative on error" code path (not
that any of our current output drivers can trigger it anyway).
A final consequence of this patch is that the responsibility to prepend
line feeds with carriage returns is moved into the output driver
implementations. Doing this only makes sense for drivers with explicit
cursor position control (i.e. serial or video), and things like the
CBMEM console that appears like a normal file to the system really have
no business containing carriage returns (we don't want people to
accidentally associate us with Windows, now, do we?).
BUG=chrome-os-partner:18390
TEST=Made sure video and CBMEM console still look good, tried printf()
with as many weird edge-case strings as I could find and compared serial
output as well as sprintf() return value.
Original-Change-Id: Ie05ae489332a0103461620f5348774b6d4afd91a
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/196384
Original-Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
(cherry picked from commit ab1ef0c07736fe1aa3e0baaf02d258731e6856c0)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Change-Id: I78f5aedf6d0c3665924995cdab691ee0162de404
Reviewed-on: http://review.coreboot.org/7880
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
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|---|---|---|
| .. | ||
| arch | ||
| bin | ||
| configs | ||
| crypto | ||
| curses | ||
| drivers | ||
| include | ||
| libc | ||
| libcbfs | ||
| liblzma | ||
| libpci | ||
| sample | ||
| tests | ||
| util | ||
| Config.in | ||
| Doxyfile | ||
| LICENSES | ||
| Makefile | ||
| Makefile.inc | ||
| README | ||
-------------------------------------------------------------------------------
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.