Thanks for your report. This is a known regression on our implementation
of f64_div, introduced by cf07323d49 ("fpu/softfloat: re-factor div",
2018-02-21).We are working on improving FP tests to limit regressions, e.g. see this thread, where the bug you report is first mentioned: https://lists.gnu.org/archive/html/qemu-devel/2018-09/msg01703.html ** Changed in: qemu Status: New => Confirmed -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1793119 Title: Wrong floating-point emulation on AArch64 with FPCR set to zero Status in QEMU: Confirmed Bug description: On AArch64, with FPCR set to Zero (i.e., FPU set to IEEE-754 compliant mode), floating-point emulation does not produce the same results as real hardware (e.g., Raspberry Pi 3 with AArch64 Linux). I attached a sample that reproduces the issue. It divides `x` by `y` and puts the result in `r`. The expected result of the operation is `q`. Output on real hardware: ========================================================= fpcr = 0x07000000. x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x7ff0000000000000. q = 0x43300fde9cbcf023. fpcr = 0x00000000. x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x43300fde9cbcf023. q = 0x43300fde9cbcf023. ========================================================= Notice that after setting FPCR to zero, `r` equals `q`. Output on qemu 3.0.0 (Linux user-mode emulation): ========================================================= fpcr = 0x07000000. x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x7ff0000000000000. q = 0x43300fde9cbcf023. fpcr = 0x00000000. x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x43300fde9cbcf024. q = 0x43300fde9cbcf023. ========================================================= Notice that after setting FPCR to zero, `r` is not equal to `q`. Also notice that, using another proprietary operating system, the same issue arises between a real board and QEMU. This might be an issue in emulation of the AArch64 instruction "fdiv". Build command line: aarch64-linux-gnu-gcc -static -O0 -o sample1 sample1.c To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1793119/+subscriptions
