Tim Northover
2014-Dec-18 04:02 UTC
[LLVMdev] Newbee question: LLVM backend regression tests for thumb1 targets on simulator possible?
> You have some special version of qemu? My default distribution's qemu > package did not have a cortex-M0 nor has qemu head freshly taken from git:The trouble with Cortex-M0 (from a virtualised testing perspective) is that it doesn't have an MMU, so any "real" operating system environment will be far more artificial than we'd like, and probably very low down on qemu's list of priorities to boot. Testing a Thumb1 CPU with an MMU (I'm sure there are ARM11* CPUs with MMU but before Thumb2, but would need to dig into which is closest to v6m) would cover *most* issues, but obviously not the ways in which Cortex-M0 is closer to v7 than v6. Tim.
Renato Golin
2014-Dec-19 10:00 UTC
[LLVMdev] Newbee question: LLVM backend regression tests for thumb1 targets on simulator possible?
On 18 December 2014 at 04:02, Tim Northover <t.p.northover at gmail.com> wrote:>> You have some special version of qemu? My default distribution's qemu >> package did not have a cortex-M0 nor has qemu head freshly taken from git: > > The trouble with Cortex-M0 (from a virtualised testing perspective) is > that it doesn't have an MMU, so any "real" operating system > environment will be far more artificial than we'd like, and probably > very low down on qemu's list of priorities to boot. > > Testing a Thumb1 CPU with an MMU (I'm sure there are ARM11* CPUs with > MMU but before Thumb2, but would need to dig into which is closest to > v6m) would cover *most* issues, but obviously not the ways in which > Cortex-M0 is closer to v7 than v6.Why not test on real hardware? https://developer.mbed.org/platforms/DipCortex-M0/ cheers, --renato
Bjoern Haase
2014-Dec-19 10:29 UTC
[LLVMdev] Newbee question: LLVM backend regression tests for thumb1 targets on simulator possible?
Am 19.12.2014 11:00, schrieb Renato Golin:> On 18 December 2014 at 04:02, Tim Northover <t.p.northover at gmail.com> wrote: >>> You have some special version of qemu? My default distribution's qemu >>> package did not have a cortex-M0 nor has qemu head freshly taken from git: >> The trouble with Cortex-M0 (from a virtualised testing perspective) is >> that it doesn't have an MMU, so any "real" operating system >> environment will be far more artificial than we'd like, and probably >> very low down on qemu's list of priorities to boot. >> >> >> Why not test on real hardware? >> >> https://developer.mbed.org/platforms/DipCortex-M0/ >> >> cheers, >> --renato >>Of course, it would not be bad to run also some limited tests on real-world hardware. However, the answer why "why not"... is in my opinion: Because you will have big difficulties matching existing regression test code (designed for bigger targets) to a system being constrained to say 16k Flash and 4k RAM. My experience with the testsuite of gcc being run on microcontrollers (AVR in this case) is that you encounter so many pseudo failures just because the test cases don't account for the limitations of the DUT that it's a tedious work to get any useful information out of the results. Imagine, e.g. a test that uses alloca and tests for correct stack pointer re-adjustment from frame pointers and just allocate two buffers of 2k RAM. In my opinion there is more need for a regression test framework in a simulation environment in a first step. Of course an optional, second step with tests on real-world HW would not hurt. Actually qemu does not seem to be this bad for this purpose. Björn.
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