Public bug reported: Using mtfsf instruction can clear the FPSCR FI bit incorrectly. This code snippet exhibits the issue: -- fpscr.ll = 0x1fffffff; __builtin_mtfsf (0b11111111, fpscr.d); fpscr.d = __builtin_mffs (); --
On POWER9 hardware: mffs : FPSCR = 0x000000007ffff7ff On qemu (git master; "-cpu POWER9"): -- $ ./mtfsf mffs : FPSCR = 0x000000007ffdffff -- Two differences: bit 52: "reserved", so maybe a "don't care" case bit 46: "FI" $ git log -1 master commit 89ea03a7dc83ca36b670ba7f787802791fcb04b1 Merge: 019217c 2531164 Author: Peter Maydell <peter.mayd...@linaro.org> Date: Mon Sep 9 09:48:34 2019 +0100 I tracked the clear is coming from do_float_check_status, likely the one in gen_mtfsf, but then I get lost figuring out what _should_ be happening. :-/ Test attached. ** Affects: qemu Importance: Undecided Status: New ** Attachment added: "test case - mtfsf clears FI" https://bugs.launchpad.net/bugs/1843795/+attachment/5288363/+files/mtfsf.c -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1843795 Title: 'mtfsf' instruction can clear FI incorrectly Status in QEMU: New Bug description: Using mtfsf instruction can clear the FPSCR FI bit incorrectly. This code snippet exhibits the issue: -- fpscr.ll = 0x1fffffff; __builtin_mtfsf (0b11111111, fpscr.d); fpscr.d = __builtin_mffs (); -- On POWER9 hardware: mffs : FPSCR = 0x000000007ffff7ff On qemu (git master; "-cpu POWER9"): -- $ ./mtfsf mffs : FPSCR = 0x000000007ffdffff -- Two differences: bit 52: "reserved", so maybe a "don't care" case bit 46: "FI" $ git log -1 master commit 89ea03a7dc83ca36b670ba7f787802791fcb04b1 Merge: 019217c 2531164 Author: Peter Maydell <peter.mayd...@linaro.org> Date: Mon Sep 9 09:48:34 2019 +0100 I tracked the clear is coming from do_float_check_status, likely the one in gen_mtfsf, but then I get lost figuring out what _should_ be happening. :-/ Test attached. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1843795/+subscriptions