On Friday, 12 March 2021, Maciej W. Rozycki wrote: > On Fri, 12 Mar 2021, Philippe Mathieu-Daudé wrote: > > > >>> Is there any way we can do this with a distro that isn't Gentoo > > >>> so that we can get a container build that is fast enough to be > > >>> useful for CI ? > > > > Using the Debian cross image I get: > > > > /home/phil/source/qemu/tests/docker/docker.py --engine auto cc --cc > > mips64el-linux-gnuabi64-gcc -i qemu/debian-mips64el-cross -s > > /home/phil/source/qemu -- -Wall -Werror -O0 -g -fno-strict-aliasing > > -mabi=n32 -march=r5900 > > /home/phil/source/qemu/tests/tcg/mips/test-r5900-dmult.c -o > > test-r5900-dmult -static > > cc1: error: unsupported combination: -march=r5900 -mhard-float > > -mdouble-float > > > > No clue what is setting '-mhard-float -mdouble-float' yet. > > The R5900 has an FPU that only supports the single floating-point format. > It's also not an IEEE 754 format. The Linux kernel ABI does support the > double and also the single floating-point format, both compliant with IEEE > 754. > > In the absence of a suitable FPU emulation code included with the kernel > will handle the missing instructions (you can use the `nofpu' kernel > parameter to force that in the presence of an FPU too). Beware however > that a recent change to the Linux kernel made FPU emulation code optional > to suit some deeply embedded applications known never to use FPU machine > instructions. > > NB the presence of emulation is always required for MIPS ISA compliance > if FPU machine instructions are ever to be used in a given application, > because operations are allowed to trap regardless and rely on emulation. > > I don't know what you are trying to achieve,
I believe Philippe is trying to compile https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg04565.html testing this: The R5900 reports itself as MIPS III but does not implement DMULT. Verify that DMULT is emulated properly in user mode by multiplying two 64-bit numbers to produce a 128-bit number. with this piece of code (notice the mips3 ISA directive for DMULT): /* * Test DMULT. */ #include <stdio.h> #include <inttypes.h> #include <assert.h> struct hi_lo { int64_t hi; uint64_t lo; }; static struct hi_lo dmult(int64_t rs, int64_t rt) { int64_t hi; uint64_t lo; /* * The R5900 reports itself as MIPS III but does not implement DMULT. * Verify that DMULT is emulated properly in user mode. */ __asm__ __volatile__ ( " .set mips3\n" " dmult %2, %3\n" " mfhi %0\n" " mflo %1\n" : "=r" (hi), "=r" (lo) : "r" (rs), "r" (rt)); return (struct hi_lo) { .hi = hi, .lo = lo }; } int main() { /* Verify that multiplying two 64-bit numbers yields a 128-bit number. */ struct hi_lo r = dmult(2760727302517, 5665449960167); assert(r.hi == 847887); assert(r.lo == 7893651516417804947); return 0; } > but your two options to choose from are: > > 1. Build for the soft-float ABI (`-msoft-float') where any FP calculations > are compiled such as to be made by the CPU using integer arithmetic. > > 2. Build for a generic MIPS ISA, for the R5900/n32 that would be MIPS III > (`-march=mips3'), and rely on the kernel FPU emulation. Note that some > integer MIPS III operations are missing too from the R5900 and have to > be emulated by the kernel for MIPS/Linux n32 psABI compliance (an > implementation can be pinched from an old libgcc version that was still > under GNU GPLv2 or another algorithm reused, e.g. my `__div64_32' piece > easily adapted). So qemu/tests/tcg/mips/Makefile.target is patched with # r5900 is only 64 bit little-endian ifneq ($(findstring 64el,$(TARGET_NAME)),) MIPS_TESTS += test-r5900-dmult test-r5900-dmult: CFLAGS += -mabi=n32 -march=r5900 endif I didn't have issues with the -mhard-float -mdouble-float flags at the time, and I didn't use mips64el-linux-gnuabi64-gcc for Debian. Fredrik
