coreboot/payloads/libpayload
Julius Werner 9c0a914192 libpayload: Fix printf edge cases for precision
This patch fixes a number of rare edge cases in handling the precision
argument in printf. The existing printf implementation used 0 as the
sentinel value for "no precision provided", which makes sense for
integers (where 0 precision has the same effect as no precision, since
in both cases no extra zeroes will be added to the front). However, for
strings it can make an important difference, since callers may expect
that they can use `printf("%.*s", len, str)` to guarantee that `str`
doesn't get dereferenced when `len` is 0. Therefore, change the
implementation so that negative values are used to represent "no
precision provided", and 0 is a legitimate value.

print_string() also had the problem that it called strlen() on the
string before even evaluating the precision. That of course defeats the
purpose of the common "%.*s" pattern to access unterminated strings.
This patch fixes the problem.

Finally, this patch slightly modifies the behavior when printing a NULL
pointer as a string, to make sure width and precision values are still
taken into account in that case, and to change from `(NULL)` to `(null)`
to match the behavior in glibc.

Change-Id: I787c18e1d33006842cf758aeb87710f80f0e5a40
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/89837
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
2025-11-04 23:14:13 +00:00
..
arch libpayload/arch/arm64/mmu: Fix missing CBMEM in used ranges 2025-06-13 15:23:09 +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 tree: Replace union {0} initializers with {} for C23 compliance 2025-08-11 16:40:34 +00:00
drivers libpayload/drivers/pci_qcom: Fix address during ATU config 2025-07-30 17:54:17 +00:00
gdb libpayload: gdb: Make die_if() format string a literal 2024-03-19 22:50:03 +00:00
include Revert "libpayload: Define UCHAR_MAX/CHAR_MIN/CHAR_MAX" 2025-10-14 09:58:49 +00:00
libc libpayload: Fix printf edge cases for precision 2025-11-04 23:14:13 +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: Fix strsep() edge cases 2025-08-13 17:44:31 +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 tree: Replace scan-build by clang-tidy 2025-07-01 01:12:32 +00:00
Makefile.mk payloads/libpayload/Makefile.mk: Replace nm with $(NM) 2025-06-05 13:37:27 +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.