[seL4] Re: memory zero'ing

On Fri, Mar 10, 2023 at 3:28 PM Kent Mcleod wrote:

On Sat, 11 Mar 2023, 09:40 Sam Leffler via Devel, wrote:

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I'm chasing an issue that looks like retype'd memory has nonsense data. If I read the kernel code correctly it looks like the object returned by an seL4_UntypeRetype syscall should be zero'd (looks to happen when an untyped memory object is reset here https://github.com/seL4/seL4/blob/master/src/object/untyped.c#L254). Is that correct? I don't see anything called out in the manual

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If the untyped isn't device untyped then it should be zeroed before it is typed into an object. Device untyped is not allowed to be accessed by the kernel and so is not written to.

When are you observing the odd behaviour?

I've got a stress test that forces lots of memory recycling by creating, running & tearing down applications. I repeatedly see a particular point in the test (after memory starts being recycled) where an app gets an instruction fault. Narrowing the issue has been challenging so I'm questioning everything (including cache handling). This is all anonymous memory.

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