tool: create IPC buffer in the tool, not the ELF#532
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midnightveil
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OK, figured out the issue: seL4/seL4#1693. Annoyingly this complicates things, but oh well. |
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A couple of small things from me but other than that looks good.
| // Workaround: https://github.com/seL4/seL4/issues/1693 | ||
| #if seL4_UserTop == 0x00ffffffffff || seL4_UserTop == 0x0fffffffffff || seL4_UserTop == 0x7fffffffffff | ||
| #define user_top_aligned (seL4_UserTop + 1) | ||
| #elif (seL4_UserTop & ((1ULL << seL4_PageBits) - 1)) != 0 | ||
| #error "Expects seL4_UserTop to be aligned" | ||
| #else | ||
| #define user_top_aligned (seL4_UserTop) | ||
| #endif |
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Suggestion: can we fix this in the kernel first? I dislike having workarounds like this, because then we have to go back and fix it later.
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It depends on proof updates to seL4, as the values are used inside seL4 implementation.
I suppose @lsf37 can comment if it would be possible to fix seL4/seL4#1693 before the next release.
We could do something hacky where we export a different value than what seL4 uses in the code, and so we make userspace consistent whilst leaving the checks the same. I don't suppose the semantics extraction is clever enough to do constant folding, would it?
e.g. if we changed a seL4_UserTop that is 0x800000000 to 0x7fffffffffff and then made the check inside the vspace map functions do (>= (seL4_UserTop + 1)). Whether it's smart enough to constant fold and not affect the proofs?
But I don't know if it's worth doing that as opposed to just fixing it... (it's surely just changing < to <= in a few places?).
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The semantics extraction does not do constant folding as such, but a lot of the times it is done implicitly in the proofs, so it would be possible to be lucky on that one.
I currently don't have it on the list for the release, because I wanted to focus on bugs, but it would not be hard to add once we have decided what to do. The tricky part is social: technically this changes the API and is a breaking change. I don't really want to write an entire RFC for this, but a few more opinions would be good.
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But I don't know if it's worth doing that as opposed to just fixing it... (it's surely just changing < to <= in a few places?).
In the code, yes. In the proofs it's slightly more than that, because one version needs a proof of absence of overflow and the other does not. It's small, but it's not automatic.
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This removes the need for the linker script to define the IPC buffer. Signed-off-by: Julia Vassiliki <julia.vassiliki@unsw.edu.au>
Turns out the SDF parser does check for overlap with the stack, so we don't need to duplicate this here, only doing ELF. Signed-off-by: Julia Vassiliki <julia.vassiliki@unsw.edu.au>
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This removes the need for the linker script to define the IPC buffer.
Fixes: #451.