loopz/loopnz clearing previous instruction's modified flags on cx -> 0
Bug #1888165 reported by
Jeffrey
This bug affects 1 person
| Affects | Status | Importance | Assigned to | Milestone | |
|---|---|---|---|---|---|
| QEMU |
Fix Released
|
Undecided
|
Richard Henderson | ||
Bug Description
If you run QBasic in qemu, printing a double-type single-digit number will print an extra decimal point (e.g. PRINT CDBL(3) prints "3.") that does not appear when running on a real CPU (or on qemu with -enable-kvm). I tracked this down to the state of the status flags after a loopnz instruction.
After executing a sequence like this in qemu:
mov bx,1
mov cx,1
dec bx ; sets Z bit in flags
A: loopnz A ; should not modify flags
Z is incorrectly clear afterwards. loopz does the same thing (but not plain loop). Interestingly, inserting pushf+popf after dec results in Z set, so loopnz/loopz does not always clear Z itself but is rather interfering with the previous instruction's flag setting.
Version 5.1.0-rc0, x86-64 host.
Revision history for this message
| Jeffrey (jmmorlan) wrote | #1 |
Revision history for this message
| Jeffrey (jmmorlan) wrote | #2 |
| Changed in qemu: | |
| status: | New → In Progress |
| assignee: | nobody → Richard Henderson (rth) |
| Changed in qemu: | |
| status: | In Progress → Fix Committed |
Revision history for this message
| Thomas Huth (th-huth) wrote | #3 |
| Changed in qemu: | |
| status: | Fix Committed → Fix Released |
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