| commit | b7832de0260b042c25bf8f53abcb32e20a29ae9c | [log] [tgz] |
|---|---|---|
| author | Jeremy Compostella <jeremy.compostella@intel.com> | Wed Aug 30 15:42:09 2023 -0700 |
| committer | Julius Werner <jwerner@chromium.org> | Thu Sep 14 21:02:07 2023 +0000 |
| tree | dea12cf2118d848e1681254d52fa26a15fc008b4 | |
| parent | 79f2e1fc8b6192e96f99c05f71baeb77d4633d40 [diff] |
x86: Add .data section support for pre-memory stages
x86 pre-memory stages do not support the `.data` section and as a
result developers are required to include runtime initialization code
instead of relying on C global variable definition.
To illustrate the impact of this lack of `.data` section support, here
are two limitations I personally ran into:
1. The inclusion of libgfxinit in romstage for Raptor Lake has
required some changes in libgfxinit to ensure data is initialized at
runtime. In addition, we had to manually map some `.data` symbols in
the `_bss` region.
2. CBFS cache is currently not supported in pre-memory stages and
enabling it would require to add an initialization function and
find a generic spot to call it.
Other platforms do not have that limitation. Hence, resolving it would
help to align code and reduce compilation based restriction (cf. the
use of `ENV_HAS_DATA_SECTION` compilation flag in various places of
coreboot code).
We identified three cases to consider:
1. eXecute-In-Place pre-memory stages
- code is in SPINOR
- data is also stored in SPINOR but must be linked in Cache-As-RAM
and copied there at runtime
2. `bootblock` stage is a bit different as it uses Cache-As-Ram but
the memory mapping and its entry code different
3. pre-memory stages loaded in and executed from
Cache-As-RAM (cf. `CONFIG_NO_XIP_EARLY_STAGES`).
eXecute-In-Place pre-memory stages (#1) require the creation of a new
ELF segment as the code segment Virtual Memory Address and Load Memory
Address are identical but the data needs to be linked in
cache-As-RAM (VMA) but to be stored right after the code (LMA).
Here is the output `readelf --segments` on a `romstage.debug` ELF
binary.
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000080 0x02000000 0x02000000 0x21960 0x21960 R E 0x20
LOAD 0x0219e0 0xfefb1640 0x02021960 0x00018 0x00018 RW 0x4
Section to Segment mapping:
Segment Sections...
00 .text
01 .data
Segment 0 `VirtAddr` and `PhysAddr` are at the same address while they
are totally different for the Segment 1 holding the `.data`
section. Since we need the data section `VirtAddr` to be in the
Cache-As-Ram and its `PhysAddr` right after the `.text` section, the
use of a new segment is mandatory.
`bootblock` (#2) also uses this new segment to store the data right
after the code and load it to Cache-As-RAM at runtime. However, the
code involved is different.
Not eXecute-In-Place pre-memory stages (#3) do not really need any
special work other than enabling a data section as the code and data
VMA / LMA translation vector is the same.
TEST=#1 and #2 verified on rex and qemu 32 and 64 bits:
- The `bootblock.debug`, `romstage.debug` and
`verstage.debug` all have data stored at the end of the `.text`
section and code to copy the data content to the Cache-As-RAM.
- The CBFS stages included in the final image has not improperly
relocated any of the `.data` section symbol.
- Test purposes global data symbols we added in bootblock,
romstage and verstage are properly accessible at runtime
#3: for "Intel Apollolake DDR3 RVP1" board, we verified that the
generated romstage ELF includes a .data section similarly to a
regular memory enabled stage.
Change-Id: I030407fcc72776e59def476daa5b86ad0495debe
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77289
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
coreboot is a Free Software project aimed at replacing the proprietary firmware (BIOS/UEFI) found in most computers. coreboot performs the required hardware initialization to configure the system, then passes control to a different executable, referred to in coreboot as the payload. Most often, the primary function of the payload is to boot the operating system (OS).
With the separation of hardware initialization and later boot logic, coreboot is perfect for a wide variety of situations. It can be used for specialized applications that run directly in the firmware, running operating systems from flash, loading custom bootloaders, or implementing firmware standards, like PC BIOS services or UEFI. This flexibility allows coreboot systems to include only the features necessary in the target application, reducing the amount of code and flash space required.
All source code for coreboot is stored in git. It is downloaded with the command:
git clone https://review.coreboot.org/coreboot.git.
Code reviews are done in the project's Gerrit instance.
The code may be browsed via coreboot's Gitiles instance.
The coreboot project also maintains a mirror of the project on github. This is read-only, as coreboot does not accept github pull requests, but allows browsing and downloading the coreboot source.
After the basic initialization of the hardware has been performed, any desired "payload" can be started by coreboot.
See https://doc.coreboot.org/payloads.html for a list of some of coreboot's supported payloads.
The coreboot project supports a wide range of architectures, chipsets, devices, and mainboards. While not all of these are documented, you can find some information in the Architecture-specific documentation or the SOC-specific documentation.
For details about the specific mainboard devices that coreboot supports, please consult the Mainboard-specific documentation or the Board Status pages.
Releases are currently done by coreboot every quarter. The release archives contain the entire coreboot codebase from the time of the release, along with any external submodules. The submodules containing binaries are separated from the general release archives. All of the packages required to build the coreboot toolchains are also kept at coreboot.org in case the websites change, or those specific packages become unavailable in the future.
All releases are available on the coreboot download page.
Please note that the coreboot releases are best considered as snapshots of the codebase, and do not currently guarantee any sort of extra stability.
The coreboot build, associated utilities and payloads require many additional tools and packages to build. The actual coreboot binary is typically built using a coreboot-controlled toolchain to provide reproducibility across various platforms. It is also possible, though not recommended, to make it directly with your system toolchain. Operating systems and distributions come with an unknown variety of system tools and utilities installed. Because of this, it isn't reasonable to list all the required packages to do a build, but the documentation lists the requirements for a few different Linux distributions.
To see the list of tools and libraries, along with a list of instructions to get started building coreboot, go to the Starting from scratch tutorial page.
That same page goes through how to use QEMU to boot the build and see the output.
Further details on the project, as well as links to documentation and more can be found on the coreboot website:
You can contact us directly on the coreboot mailing list:
https://doc.coreboot.org/community/forums.html
There are many files in the coreboot tree that we feel are not copyrightable due to a lack of creative content.
"In order to qualify for copyright protection in the United States, a work must satisfy the originality requirement, which has two parts. The work must have “at least a modicum” of creativity, and it must be the independent creation of its author."
https://guides.lib.umich.edu/copyrightbasics/copyrightability
Similar terms apply to other locations.
These uncopyrightable files include:
As non-creative content, these files are in the public domain by default. As such, the coreboot project excludes them from the project's general license even though they may be included in a final binary.
If there are questions or concerns about this policy, please get in touch with the coreboot project via the mailing list.
The copyright on coreboot is owned by quite a large number of individual developers and companies. A list of companies and individuals with known copyright claims is present at the top level of the coreboot source tree in the 'AUTHORS' file. Please check the git history of each of the source files for details.
Because of the way coreboot began, using a significant amount of source code from the Linux kernel, it's licensed the same way as the Linux Kernel, with GNU General Public License (GPL) Version 2. Individual files are licensed under various licenses, though all are compatible with GPLv2. The resulting coreboot image is licensed under the GPL, version 2. All source files should have an SPDX license identifier at the top for clarification.
Files under coreboot/Documentation/ are licensed under CC-BY 4.0 terms. As an exception, files under Documentation/ with a history older than 2017-05-24 might be under different licenses.
Files in the coreboot/src/commonlib/bsd directory are all licensed with the BSD-3-clause license. Many are also dual-licensed GPL-2.0-only or GPL-2.0-or-later. These files are intended to be shared with libpayload or other BSD licensed projects.
The libpayload project contained in coreboot/payloads/libpayload may be licensed as BSD or GPL, depending on the code pulled in during the build process. All GPL source code should be excluded unless the Kconfig option to include it is set.
Since 2017, coreboot has been a member of The Software Freedom Conservancy, a nonprofit organization devoted to ethical technology and driving initiatives to make technology more inclusive. The conservancy acts as coreboot's fiscal sponsor and legal advisor.