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Documentation: Update 4.22 release notes with x86 .data section 

Change-Id: I2d6d611df8930ad0c473489eacee9019cbdacb9e
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78000
Reviewed-by: Bora Guvendik <bora.guvendik@intel.com>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
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Jeremy Compostella 2023-09-18 13:47:09 -07:00 committed by Martin L Roth
parent 75f0b607fa
commit 8e4f6e90bf
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Documentation/releases/coreboot-4.22-relnotes.md
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@ -19,6 +19,46 @@ Update this document with changes that should be in the release notes.
* This section should have full descriptions and can or should have
a link to the referenced commits.
### x86: support .data section for pre-memory stages
x86 pre-memory stages did not support the `.data` section and as a
result developers were required to include runtime initialization code
instead of relying on C global variable definition.
Other platforms do not have that limitation. Hence, resolving it helps
to align code and reduce compilation based restriction (cf. the use of
`ENV_HAS_DATA_SECTION` compilation flag in various places of coreboot
code).
There were three types of binary to consider:
1. eXecute-In-Place pre-memory stages
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) relies on 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).
`bootblock` (#2) also uses this new segment to store the data right
after the code and it loads it to Cache-As-RAM at runtime. However,
the code involved is different.
Not eXecute-In-Place pre-memory stages (#3) did not really need any
special work other than enabling a .data section as the code and data
VMA / LMA translation vector is the same.
Related important commits:
- c9cae530e5ac54c5b3639d0d555966ca5cad65ff ("cbfstool: Make add-stage
support multiple ignore sections")
- 79f2e1fc8b6192e96f99c05f71baeb77d4633d40 ("cbfstool: Make add-stage
support multiple loadable segments")
- b7832de0260b042c25bf8f53abcb32e20a29ae9c ("x86: Add .data section
support for pre-memory stages")
### Toolchain updates
* Upgrade GMP from 6.2.1 to 6.3.0