vboot: Disallow separate verstage after romstage, try to clarify logic

Hardware / Coreboot - Julius Werner [chromium.org] - 28 March 2017 16:17 EDT

No board has ever tried to combine CONFIG_SEPARATE_VERSTAGE with CONFIG_VBOOT_STARTS_IN_ROMSTAGE. There are probably many reasons why this wouldn't work (e.g. x86 CAR migration logic currently always assumes verstage code to run pre-migration). It would also not really make sense: the reason we use separate verstages is to decrease bootblock size (mitigating the boot speed cost of slow boot ROM SPI drivers) and to allow the SRAM-saving RETURN_FROM_VERSTAGE trick, neither of which would apply to the after-romstage case. It is better to just forbid that case explicitly and give programmers more guarantees about what the verstage is (e.g. now the assumption that it runs pre-RAM is always valid).

Since Kconfig dependencies aren't always guaranteed in the face of 'select' statements, also add some explicit compile-time assertions to the vboot code. We can simplify some of the loader logic which now no longer needs to provide for the forbidden case. In addition, also try to make some of the loader logic more readable by writing it in a more functional style that allows us to put more assertions about which cases should be unreachable in there, which will hopefully make it more robust and fail-fast with future changes (e.g. addition of new stages).

Change-Id: Iaf60040af4eff711d9b80ee0e5950ce05958b3aa

73d042b vboot: Disallow separate verstage after romstage, try to clarify logic
src/include/memlayout.h | 5 ++-
src/vboot/Kconfig | 8 ++++-
src/vboot/vboot_loader.c | 84 ++++++++++++++++++++++--------------------------
3 files changed, 50 insertions(+), 47 deletions(-)

Upstream: review.coreboot.org

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