break dependency on Linux about riscv-binutils-gdb HOT 7 CLOSED

I would favor not depending on the current time at all; it makes the simulator nondeterministic. Could just use an affine function of the instructions-retired counter.

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Could it be the same as instructions-retired? Maybe just instructions-retired x 2?

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something like that would probably be ok

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(in spike, they are equal)

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clock_gettime is not Linux specific. it's explicitly in POSIX:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/clock_getres.html

we can fallback to CLOCK_MONOTONIC if CLOCK_BOOTTIME is not available. getimeofday is not appropriate as it's not monotonic -- it can be rewound. any C++ lib is not appropriate as the GNU sim is C only, and doesn't rely on external C++ libs.

if none of those are available because the OS is crap, we can fallback to csr.instret.

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Trying all three is a reasonable approach, too... @vapier what do you think about the tradeoff between having an accurate time and having deterministic simulator runs?

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This is fixed, CSR_TIME now returns the cycle count.

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