cbfstool: Fix offset calculation for aligned files

Hardware / Coreboot - Julius Werner [chromium.org] - 7 December 2021 16:59 UTC

The placement calculation logic in cbfs_add_component() has become quite a mess, and this patch can only fix that to a limited degree. The interaction between all the different pathways of how the `offset`
variable can be set and at what point exactly the final placement offset is decided can get quite convoluted. In particular, one existing problem is that the offset for a file added with the --align flag is decided before the convert() function is called, which may change the form (and thereby the size) of the file again after its location was found --resulting in a location that ends up being too small, or being unable to find a location for a file that should fit. This used to be okay under the assumption that forced alignment should really only be necessary for use cases like XIP where the file is directly "used" straight from its location on flash in some way, and those cases can never be compressed-- however, recent AMD platforms have started using the --align flag to meet the requirements of their SPI DMA controller and broken this assumption.

This patch fixes that particular problem and hopefully eliminates a bit of the convolution by moving the offset decision point in the --align case after the convert() step. This is safe when the steps in-between (add_topswap_bootblock() and convert() itself) do not rely on the location having already been decided by --align before that point. For the topswap case this is easy, because in practice we always call it with --base-address (and as far as I can tell that's the only way it was ever meant to work?) -- so codify that assumption in the function. For convert() this mostly means that the implementations that do touch the offset variable (mkstage and FSP) need to ensure they take care of the alignment themselves. The FSP case is particularly complex so I tried to rewrite the code in a slightly more straight-forward way and clearly document the supported cases, which should hopefully make it easier to see that the offset variable is handled correctly in all of them. For mkstage the best solution seems to be to only have it touch the offset
variable in the XIP case (where we know compression must be disabled, so we can rely on it not changing the file size later), and have the extra space for the stage header directly taken care of by do_cbfs_locate() so that can happen after convert().

NOTE: This is changing the behavior of `cbfstool add -t fsp` when neither --base-address nor --xip are passed (e.g. FSP-S). Previously, cbfstool would implicitly force an alignment of 4K. As far as I can tell from the comments, this is unnecessary because this binary is loaded into RAM and CBFS placement does not matter, so I assume this is an oversight caused by accidentally reusing code that was only meant for the XIP case.

6ddacd6f5b cbfstool: Fix offset calculation for aligned files
util/cbfstool/cbfstool.c | 150 ++++++++++++++++++++++++++---------------------
1 file changed, 82 insertions(+), 68 deletions(-)

Upstream: review.coreboot.org


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