CMake test for processor feature

Question

I am wondering if it is possible for CMake to run tests like one might run with a configure script. Specifically I want to test if the system I am compiling on has support for

Answer 1

Selecting line 19 exactly makes this brittle. On my desktop (Linux 4.20 on i7-6700k), that line is

wp              : yes

Instead use grep's pattern-matching ability to check for the flags\t\t: line.

grep -l '^flags[[:space:]]*:.*rdtscp' /proc/cpuinfo prints the filename and exits with success after the first match. Or prints nothing and exists with failure status if it doesn't find a match.

I don't know CMake, but based on the other answer presumably you'd use

execute_process(COMMAND grep -l '^flags[[:space:]]*:.*rdtscp' /proc/cpuinfo
    OUTPUT_VARIABLE OUT)

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The simpler version of this is just grep -l rdtscp /proc/cpuinfo, but requiring a match in the flags : line will prevent any possible false-positive. (To be even more belt-and-suspenders, you could require space or end of line before/after, maybe with PCREgrep for zero-width assertions. In case some future feature flag like XYZrdtscpABC that can be present without RDTSCP support becomes a thing in the future. Or like broken_rdtscp). Or we could just assume that rdtscp is never at the end of the a line and look for ^flags.*:.* rdtscp.

Using -l gets grep to exit after the first match, in case you were using head/tail as an optimization to avoid processing more lines on massively multi-core systems like Xeon Phi? It will still read the whole file if there's no match for rdtscp, but probably any massively-multi-core system will have RDTSCP. And grep is very fast anyway.

Answer 2

execute_process(COMMAND cat /proc/cpuinfo
    COMMAND head -n 19
    COMMAND tail -1
    COMMAND grep -c rdtscp
    OUTPUT_VARIABLE OUT)