On Wed, Dec 8, 2010 at 1:34 PM, Peter Maydell <peter.mayd...@linaro.org> wrote: > On 8 December 2010 12:57, Dave Martin <dave.mar...@linaro.org> wrote: >> On Wed, Dec 8, 2010 at 12:04 PM, Peter Maydell <peter.mayd...@linaro.org> >> wrote: >>> Hi. As part of my work on qemu I've written a simplistic random instruction >>> sequence generator and test harness. > >> I'd thought about this sort of thing before, but there were some >> interesting challenges... >> >> Is it random random, or does it try to mould to the architectural envelope? >> >> For example, randomly choosing opcode and shift operation bits in ALU >> instructions will exercise the interpreter much more interestingly >> than randomly choosing the offset bits in a branch instruction; and >> some potentially highly interesting and error-prone instructions like >> barriers, WFE/SEV, and all that kind of thing will get basically no >> testing from a random-number generator, since they tend to map to a >> single, fixed bit pattern. > > As I say, it's pretty simplistic: I was aiming for a "good enough" tool > that would let me find and test qemu bugs. The generator works by: > * pick a pattern at random from all the ones it's using > * generate a random 32 (or 16) bits > * mask in the should-be-zero/one bits > * apply constraints (eg regs never r13 or r15, any user-specified > constraint); > if the constraint is broken then just restart with a new random number > * force the cond field to "always" a configurable proportion of the time > > So the effect is that the testing will be distributed evenly over the > given instructions even if some take a much smaller share of > encoding space. > > However for other reasons the tool isn't really suited for testing weird > things like WFE, SEV or barriers -- there's a disclaimer about this > in the README. I think for that sort of thing you'd do much better > with a rather more directed kind of testing.
Sure-- I was just curious. This doesn't mean the tool isn't useful, just that it usefully can't exercise everything (which is a sensible limitation in any case). Cheers ---Dave _______________________________________________ linaro-toolchain mailing list linaro-toolchain@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-toolchain
