coreboot/payloads/libpayload
Julius Werner df0221e62a libpayload: Protect against trying to use weak symbols in the wrong way
Weak symbols don't work as expected when you try to override them from
within the same static library. Static libraries are just archives of
individual objects, and when the linker tries to resolve a symbol
against it it simply uses the implementation from the first object that
has one, weak or not. It does not search through all remaining objects
to see if there's also a strong implementation.

We've had multiple cases in libpayload where builds were incorrectly
using the default implementation rather than an optimized arch-specific
implementation for years due to this issue. To prevent it from
recurring, this patch adds some postprocessing script to the Makefile
that checks for this situation and makes the build fail if it creeps in
again.

Change-Id: I9fcbc9b873901d126322b12954c349c08300369f
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87777
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
2025-05-26 18:40:51 +00:00
..
arch libpayload: Use Kconfig instead of weak symbol for arch_ndelay() 2025-05-22 19:27:30 +00:00
bin libpayload: Add x86_64 (64-bit) support 2024-05-26 01:26:31 +00:00
configs libpayload: configs: Add new config.featuretest to broaden CI 2024-12-04 22:25:34 +00:00
crypto payloads: Rename Makefiles from .inc to .mk 2024-01-24 10:15:10 +00:00
curses payloads: Rename Makefiles from .inc to .mk 2024-01-24 10:15:10 +00:00
drivers cbgfx: Prevent divide-by-zero edge case in Lanczos kernel 2025-05-06 21:04:04 +00:00
gdb libpayload: gdb: Make die_if() format string a literal 2024-03-19 22:50:03 +00:00
include libpayload: arm64: Reduce DMA allocator space to 1MB 2025-05-22 20:56:14 +00:00
libc libpayload: Use Kconfig instead of weak symbol for arch_ndelay() 2025-05-22 19:27:30 +00:00
libcbfs libpayload: Remove legacy CBFS API 2024-02-22 21:18:39 +00:00
liblz4 payloads: Rename Makefiles from .inc to .mk 2024-01-24 10:15:10 +00:00
liblzma payloads: Rename Makefiles from .inc to .mk 2024-01-24 10:15:10 +00:00
libpci payloads: Rename Makefiles from .inc to .mk 2024-01-24 10:15:10 +00:00
sample libpayload: Add mock architecture 2021-10-11 12:59:57 +00:00
tests libpayload: Use Kconfig instead of weak symbol for arch_ndelay() 2025-05-22 19:27:30 +00:00
vboot libpayload: Add x86_64 (64-bit) support 2024-05-26 01:26:31 +00:00
.gitignore .gitignore: Split into subdirectory files 2020-10-30 07:05:27 +00:00
Doxyfile payloads: Remove/fix trailing whitespace 2018-09-04 12:38:40 +00:00
Kconfig libpayload: Use Kconfig instead of weak symbol for arch_ndelay() 2025-05-22 19:27:30 +00:00
LICENSE_GPL libpayload: Introduce new Kconfig to explicitly allow GPL code 2015-01-09 07:06:27 +01:00
LICENSES libpayload: Add LZ4 decompression algorithm 2015-07-09 00:10:16 +02:00
Makefile libpayload: Add x86_64 (64-bit) support 2024-05-26 01:26:31 +00:00
Makefile.mk libpayload: Protect against trying to use weak symbols in the wrong way 2025-05-26 18:40:51 +00:00
Makefile.payload libpayload/Makefile.payload: Add lto flags 2024-08-27 09:08:07 +00:00
README payloads/libpayload: Update a Makefile for sample libpayload 2019-06-21 09:16:36 +00:00

-------------------------------------------------------------------------------
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 https://www.coreboot.org for details on coreboot.


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

 $ git clone https://review.coreboot.org/coreboot.git

 $ cd coreboot/payloads/libpayload

 $ make menuconfig

 $ make

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

On x86 systems, libpayload will always be 32-bit even if your host OS runs
in 64-bit, so you might have to install the 32-bit libgcc version.
On Debian systems you'd do 'apt-get install gcc-multilib' for example.

Run 'make distclean' before switching boards. This command will remove
your current .config file, so you need 'make menuconfig' again or
'make defconfig' in order to set up configuration. Default configuration
is based on 'configs/defconfig'. See the configs/ directory for examples
of configuration.


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 https://www.coreboot.org/Libpayload.

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


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

See LICENSES.