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move SP setting

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Peter Ferrie 2021-11-24 12:32:14 -08:00
parent d50e78162d
commit 88e749ea79
1 changed files with 8 additions and 2 deletions
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sectorlisp.S
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@ -36,13 +36,19 @@ kCdr: .asciz "CDR" # ordering matters
kCons: .asciz "CONS" # ordering matters kCons: .asciz "CONS" # ordering matters
kEq: .asciz "EQ" # needs to be last kEq: .asciz "EQ" # needs to be last
begin: push %cs # that means ss = ds = es = cs begin: xor %sp,%sp # use highest address as stack
# set independently of SS!
# 8088 doesn't stop interrupts
# after SS is set, and PC BIOS
# sets SP to a value that will
# damage our code if int fires
# between setting SS and SP
push %cs # that means ss = ds = es = cs
pop %ds # noting ljmp set cs to 0x7c00 pop %ds # noting ljmp set cs to 0x7c00
push %cs # that's the bios load address push %cs # that's the bios load address
pop %es # therefore NULL points to NUL pop %es # therefore NULL points to NUL
push %cs # terminated NIL string above! push %cs # terminated NIL string above!
pop %ss # errata exists but don't care pop %ss # errata exists but don't care
xor %sp,%sp # use highest address as stack
mov $2,%bx mov $2,%bx
main: mov $0x8000,%cx # dl (g_look) is zero or cr main: mov $0x8000,%cx # dl (g_look) is zero or cr
call GetToken call GetToken