[Bug 1888165] Re: loopz/loopnz clearing previous instruction's modified flags on cx -> 0
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=3cb3a7720b01830abd5 ** Changed in: qemu Status: Fix Committed => Fix Released -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1888165 Title: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 Status in QEMU: Fix Released 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. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1888165/+subscriptions
[Bug 1888165] Re: loopz/loopnz clearing previous instruction's modified flags on cx -> 0
** Changed in: qemu Status: In Progress => Fix Committed -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1888165 Title: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 Status in QEMU: Fix Committed 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. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1888165/+subscriptions
[Bug 1888165] Re: loopz/loopnz clearing previous instruction's modified flags on cx -> 0
** Changed in: qemu Status: New => In Progress ** Changed in: qemu Assignee: (unassigned) => Richard Henderson (rth) -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1888165 Title: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 Status in QEMU: In Progress 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. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1888165/+subscriptions
[Bug 1888165] Re: loopz/loopnz clearing previous instruction's modified flags on cx -> 0
** Attachment added: "source" https://bugs.launchpad.net/qemu/+bug/1888165/+attachment/5394190/+files/loopnzbug.asm -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1888165 Title: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 Status in QEMU: New 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. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1888165/+subscriptions
[Bug 1888165] Re: loopz/loopnz clearing previous instruction's modified flags on cx -> 0
** Attachment added: "bootable image demonstrating bug" https://bugs.launchpad.net/qemu/+bug/1888165/+attachment/5394189/+files/loopnzbug.img -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1888165 Title: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 Status in QEMU: New 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. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1888165/+subscriptions
