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But GCC and > others do not use these interfaces, they use CPUID/XGETBV directly and > cache the result, so this reset does not alter the outcome of their > IFUNC resolvers. We are on glibc mailing list so this patch and mail thread is about glibc. I am aware other programs and libraries need their own reset. For OpenJDK JIT compiler I wrote the CPU reset already; but that is offtopic here: https://github.com/openjdk/crac/pull/41 > > The question is how to implement it. I have found > > https://github.com/ddcc/libcpuidoverride > > but it is not compatible with latest glibc (maybe its loader code needs to > > implement ELF relocations, it would be definitely fixable). > > It needs kernel support for sure. I do not know to what extent CPUID > can be context-switched at the silicon level, maybe the masking is > system-wide (or per-guest in a virtualized configuration). There is already its kernel support - ARCH_SET_CPUID. It is per process. > > Another option is GLIBC_TUNABLES=glibc.cpu.hwcaps=... although then one has to > > translate cpuid feature bits into the glibc names like SSE4_2 etc. > > Also re-exec() after setenv("GLIBC_TUNABLES") is not too nice. > > Again, that's not going to work in practice because libraries and > applications do not use . This mailing list is for glibc so let's talk about glibc. Thanks, Jan