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Tool to generate CPU_FLAGS_* for your CPU
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cpuid2cpuflags -- CPU_FLAGS_* generator (c) 2017 Michał Górny 2-clause BSD license Usage ~~~~~ The program attempts to obtain the identification and capabilities of the currently used CPU, and print the matching set of CPU_FLAGS_* flags for Gentoo. To use it, just run it: $ cpuid2cpuflags CPU_FLAGS_X86: 3dnow 3dnowext mmx mmxext sse sse2 sse3 There are no command-line options. Please note that the program identifies the apparent CPU capabilities using available CPU calls or system interfaces, *not* the capabilities indicated by compiler flags. The flag definitions match the flags described in Gentoo profiles/desc at the time of program release. If additional flags are introduced in the future, they will be added in a future program release. The output format is compatible both with Portage (package.use) and Paludis (use.conf/options.conf). If you find it useful to generate/update it automatically, you can use a dedicated file: $ mkdir /etc/portage/package.use # if not used yet $ echo "*/* $(cpuid2cpuflags)" > /etc/portage/package.use/00cpuflags Implementation details ~~~~~~~~~~~~~~~~~~~~~~ X86 (incl. x86-64) ------------------ On x86 platforms, cpuid2cpuflags issues the CPUID instruction to obtain processor capabilities. This should work reliably across different systems and kernels, unless the system somehow blocks this instruction. If this is the case, please report a bug. ARM and AArch64 --------------- On ARM platforms, the userspace processes are not allowed to obtain processor information directly. Instead, the program is relying on kernel identification of the CPU provided via the system interfaces. Currently, only Linux is supported. On Linux, two interfaces are used: uname() to identify the CPU family, and getauxval(AT_HWCAP*...) to obtain detailed feature flags. The textual value obtained from uname (armv* or aarch64) is used to enable appropriate ARM version flags and some feature flags. It is also used to determine whether the kernel is 64- or 32-bit since that affects the interpretation of AT_HWCAP* flags. Afterwards, the remaining feature flags are enabled based on either flag bits provided by AT_HWCAP*, or implicitly based on the subarchitecture (i.e. currently a number of features is always set on AArch64). It should be noted that the program strongly depends on correct identification of the CPU in the kernel. If you find the results incorrect, please report a bug but I can't promise I'll be able to find a good workaround.