mirror of
https://github.com/elliotnunn/powermac-rom.git
synced 2024-12-01 09:50:31 +00:00
4c0e5221f1
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.
62 lines
1.1 KiB
ArmAsm
62 lines
1.1 KiB
ArmAsm
;_______________________________________________________________________
|
|
; My additions to the NanoKernel, to go at the end of the code image
|
|
;_______________________________________________________________________
|
|
|
|
if &TYPE('NKDebugShim') != 'UNDEFINED'
|
|
|
|
DeclareMPCall 200, NKDebug
|
|
|
|
NKDebug
|
|
|
|
; Lifted from NKxprintf:
|
|
; Put the physical address of the r3 arg in r8
|
|
|
|
rlwinm. r9, r11, 0, MSR_DRbit, MSR_DRbit ; IntSyscall sets this
|
|
mr r8, r3
|
|
|
|
beq @already_physical
|
|
li r9, 0
|
|
bl V2P ; takes page EA in r8, r9=0, returns page PA in r17
|
|
beq @fail
|
|
rlwimi r8, r17, 0, 0, 19
|
|
@already_physical
|
|
|
|
|
|
; Copy the command into the KDP buffer reserved for this purpose:
|
|
; r8 = src
|
|
; r29 = dest
|
|
; r30 = ctr
|
|
; r31 = val
|
|
|
|
mfsprg r1, 0
|
|
lwz r1, EWA.PA_KDP(r1)
|
|
|
|
li r30, 0
|
|
addi r29, r1, -0x960
|
|
@cmdloop
|
|
lbzx r31, r8, r30
|
|
stbx r31, r29, r30
|
|
addi r30, r30, 1
|
|
cmpwi r31, 0
|
|
bne @cmdloop
|
|
|
|
lwz r31, -0x404(r1)
|
|
|
|
stw r8, -0x404(r1)
|
|
|
|
bl panic
|
|
|
|
lwz r8, -0x404(r1)
|
|
li r0, 0
|
|
stw r0, 0(r8)
|
|
|
|
stw r31, -0x404(r1)
|
|
|
|
b ReturnZeroFromMPCall
|
|
|
|
|
|
@fail
|
|
b ReturnMPCallOOM
|
|
|
|
endif
|