Whenever a field was added to the end of the Primary System Area (PSA)
record, the offsets of all other fields would change. When reversing NK
version 02.27, I noticed that 32 bytes had been added to the end of the
PSA between 02.27 and 02.28. To build a byte-perfect 02.27, all
references to PSA fields must therefore use the record definition in
NKPublic.s instead of a numeric offset.
In this commit, all PSA references are identified by field name (_FFF if
the field has not yet been reversed).
These + and - characters in a branch mnemonic can cause the assembler to
produce conditional branch instructions with that hint the branch
predictor. The default for forward branches is -, and for backward
branches is +. If a mnemonic is issued with the opposite sign, then bit
10 of the instruction (the LSB of the BO field) is set.
My long-retired "ppcdisasm" script inserted these hints unconditionally,
despite 98% of them not being required. The code is much cleaner now.
I read in some old MPW release notes that PPCAsm and PPCLink together
exhibit a quirk when linking conditional branches to imported symbols.
PPCAsm always assembles these conditional branches as if they were
forward branches (that is, a + hint will always set the hint bit, and a
- hint will never). I hoped to use this property to divine whether the
NanoKernel was linked from one or many assembly files, but I was
frustrated by the lack of conditional branches between files.
