I wonder if we want #define's for these values that are only used once vs just using them inline in the one place they are used? Shared values like BASL_OEM_ID make sense to be shared. It also looks like so far the OEM table ID is following the pattern "BV" + <ACPI SIG> + " " which could perhaps be hardcoded in the build table header function avoiding the need for specifying it at all.

I've created the defines to have a place where you can find a short overview of our tables and revisions etc. I can inline them if you want.

Regarding OEM table ID: The only usecase for different id's that I'm aware of are multiple SSDT tables (https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#secondary-system-description-table-ssdt). Not sure if it could make sense for bhyve to use SSDT tables.

We aren't likely to need SSDTs, no. I do think generating the table ID's using a pattern in the helper function might be nice as it would shrink the code slightly in all the functions building tables.

I'm going to remove it. What do you think about the oem revision field? We could hard code it to 1 to remove another parameter from basl_table_append_header but it might be helpful to bump the version for debugging purposes when we fix a table (e.g. https://reviews.freebsd.org/D36998#inline-228535)

I think keeping the revision as an argument to basl_table_append_header makes sense.