search

Baron-von-Riedesel / DOS-debug

Debug and DebugX (short: Debug/X) are extended versions of MS DEBUG
58 stars 12 forks source link

When tracing a `pushf` instruction with P the apparent TF is not reset on the stack #8

Open ecm-pushbx opened 2 years ago

ecm-pushbx commented 2 years ago

The T command has a special call to adjust the pushed flags after tracing a pushf instruction, see https://github.com/Baron-von-Riedesel/DOS-debug/blob/b60a75d445f08f9a20abc48ccfb906225194bb41/src/DEBUG.ASM#L6960

It appears this is not called when tracing with the P command, which will in turn result in an apparent TF = 1 result from the pushf instruction.

Baron-von-Riedesel commented 2 years ago

True, OTOH, this check isn't really fool-proofed ( just opcode 9Ch is checked, but - at least - 66h 9Ch may also push flags ) - so one will probably have to live with occational "unexpected interrupts".

ecm-pushbx commented 2 years ago

True, OTOH, this check isn't really fool-proofed ( just opcode 9Ch is checked, but - at least - 66h 9Ch may also push flags ) - so one will probably have to live with occational "unexpected interrupts".

True, this is why lDebug skips all prefixes before checking for pushf being traced:

    or byte [reg_efl+1], 1  ; set single-step mode (cleared when returning into DEBUG)
    xor cx, cx
    call skipprefixes
    cmp al, 9Ch     ; opcode "PUSHF"?
    jnz .notpushf

That or instruction is the only point at which lDebug sets the Trace Flag, within the function traceone. This function is also used by the P command (and TP command) if it wants to trace an instruction, instead of calling run directly. So the kitchen sink of trace features are re-used for P.