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https://git.k-space.ee/arti/vt1200.git
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48 lines
1.1 KiB
NASM
48 lines
1.1 KiB
NASM
; retprobe.asm -- MINIMAL test of the DI return-PC trampoline, no drawing.
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;
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; Installs `entry` on the DI RAM stub (00000DB0h). `entry` replaces the
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; interrupt frame's saved PC with `ret_hook` and runs the stock handler.
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; `ret_hook` bumps a marker and returns to the saved PC. It deliberately does
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; NOT preserve registers, so TCP liveness tells us whether the frame/PC dance
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; itself is sound. Scratch is in the payload's own page (01840800h).
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;
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; Linked at bit 01840000h by dwt/visual/build.sh.
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.text
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_start:
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pushst
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dint
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setf 32, 0, 0
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movi entry, a0, L
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move a0, @00000DC0h, 0
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setf 16, 0, 0
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movi 0C080h, a0, L
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move a0, @00000DB0h, 0
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sub a0, a0
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move a0, @01840800h, 0 ; marker
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popst
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rets
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entry:
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move a0, @01840810h, 1
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setf 32, 0, 1
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move *sp(020h), a0, 1
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move a0, @01840804h, 1 ; orig_pc
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movi ret_hook, a0, L
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move a0, *sp(020h), 1
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move @01840810h, a0, 1
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jauc 3F7146D0h
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ret_hook:
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move @01840800h, a0, 0
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inc a0
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move a0, @01840800h, 0
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setf 32, 0, 1
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move @01840804h, a0, 1 ; orig_pc
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move a0, -*sp, 1
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getst a0 ; (clobbers a0 on purpose)
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move a0, -*sp, 1
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popst
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rets
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.end
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