On 24.02.2026 10:34, Edwin Torok wrote: >> On 23 Feb 2026, at 16:10, Jan Beulich <[email protected]> wrote: >> On 23.02.2026 11:04, Edwin Török wrote: >>> clang-21 doesn't support `-ffixed-xmm0`, so `%xmm0` won't have the >>> expected value. >>> Disable these tests on clang. >> >> I don't think that's what we want, and not only because of the clutter the >> various #ifdef cause. We want to be able to run as many of the tests as >> possible, so the first goal should be to find some alternative mechanism to >> achieve the same effect. A global register variable comes to mind as a >> possible option. >> >> Further, how did you arrive at which tests need suppressing? > > I used gdb to look at the 2 memory areas, and noticed that the XMM region was > different between emulated and actual when built with clang. > Then I noticed the build failures due to the lack of fixed-xmm0. > Then I added the ifdefs one by one as I ran the test until the whole test > program passed without failure. > I tried adding some ‘pxor xmm0, xmm0’ into the cpu_has_sse2 sections, but > that didn’t really work either. > > Although I may have been misled by the overlapping region, see below. > >> I don't think >> we rely on an "expected value" anywhere. I don't even recall us passing >> -ffixed-xmm0 when compiling test_x86_emulate.c. > > Yes, I’m surprised it works with GCC. But maybe only because the emulator > overwrites the actual FXSAVE area corresponding to XMM. > XMM0 begins at offset 160, and 0x100 - 0x80 = 128. > AFAICT the actual execution stores its result at [0x80, 0x80+0x200), and the > emulator stores its result into [0x100, 0x100+0x200). > So the emulator will overwrite some of the values from the actual run. > > This only works if the end of the FXSAVE area looks like its beginning (i.e. > if FCW/FSW/etc. happens to match MM6/etc.)
Are you possibly overlooking the fact that res[] is an array of unsigned int elements, i.e. the offsets used in source code all need to be multiplied by 4 to give offsets in memory? Jan
