wasmtime / Issue #1216 Windows fprs preservation · git-wasmtime

Stream: git-wasmtime

Topic: wasmtime / Issue #1216 Windows fprs preservation

Wasmtime GitHub notifications bot (Mar 11 2020 at 19:43):

The CI failure is due to tripping this check that we wouldn't misreport unwind information in cases where we have callee-save floating-point registers. I tried reproducing this locally by building the module in multi_func_value/func.wast by clif-util wasm funct_module.wast --target x86_64-windows -D, but for some reason that seems to build fine, using a significantly smaller amount of stack space? I ran clif-util from Linux, but the only thing that should be a factor here is the target specification. I'm not sure why it doesn't reproduce this way. Is there a flag I should set that influences lowering to clif as well?

Anyway, I printed the faulting prologue in CI to double-check that the panic is correctly hit, and indeed a function in the module uses well over the 240-byte limit I've noted above:
x86_push.i64 v105
offset 2: copy_special %rsp -> %rbp
offset 5: x86_push.i64 v106
offset 7: x86_push.i64 v107
offset 9: x86_push.i64 v108
offset 11: x86_push.i64 v109
offset 13: x86_push.i64 v110
offset 15: x86_push.i64 v111
offset 17: adjust_sp_down_imm 336
offset 24: v112 = stack_addr.i64 ss18
offset 32: store.f64 notrap aligned v113, v112
offset 37: store.f64 notrap aligned v114, v112+16
offset 43: store.f64 notrap aligned v115, v112+32
Since this function uses callee-save floats, we miscompile it on Windows today. Should I disable this test on Windows? (not sure if there's a mechanism for this in spectests, honestly) It would be fixed in the same PR that adjusts stack layout to not be constrained to 240 byte frames when using callee-save xmm registers.

Wasmtime GitHub notifications bot (Mar 11 2020 at 19:46):

iximeow edited a comment on Issue #1216:

The CI failure is due to tripping this check that we wouldn't misreport unwind information in cases where we have callee-save floating-point registers. I tried reproducing this locally by building the module in multi_func_value/func.wast by clif-util wasm funct_module.wast --target x86_64-windows -D, but for some reason that seems to build fine, using a significantly smaller amount of stack space? I ran clif-util from Linux, but the only thing that should be a factor here is the target specification. I'm not sure why it doesn't reproduce this way. Is there a flag I should set that influences lowering to clif as well?

Anyway, I printed the faulting prologue in CI to double-check that the panic is correctly hit, and indeed a function in the module uses well over the 240-byte limit I've noted above:
x86_push.i64 v105
offset 2: copy_special %rsp -> %rbp
offset 5: x86_push.i64 v106
offset 7: x86_push.i64 v107
offset 9: x86_push.i64 v108
offset 11: x86_push.i64 v109
offset 13: x86_push.i64 v110
offset 15: x86_push.i64 v111
offset 17: adjust_sp_down_imm 336
offset 24: v112 = stack_addr.i64 ss18
offset 32: store.f64 notrap aligned v113, v112
offset 37: store.f64 notrap aligned v114, v112+16
offset 43: store.f64 notrap aligned v115, v112+32
Since this function uses callee-save floats, we miscompile it on Windows today. Should I disable this test on Windows? (not sure if there's a mechanism for this in spectests, honestly) It would be fixed in the same PR that adjusts stack layout to not be constrained to 240 byte frames when using callee-save xmm registers.

Edit: this panic is only reached if you want a fastcall function with all of:

a >240 byte stack frame

callee-save floats

unwind information

This PR fixes callee-save float preservation in fastcall functions generally. Asking for unwind information causes the panic. I'm not sure how easily Windows targets can get the former without the latter.

Wasmtime GitHub notifications bot (Mar 12 2020 at 17:11):

github-actions[bot] commented on Issue #1216:

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Wasmtime GitHub notifications bot (Mar 12 2020 at 17:17):

github-actions[bot] commented on Issue #1216:

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Wasmtime GitHub notifications bot (Mar 12 2020 at 19:16):

peterhuene deleted a comment on Issue #1216:

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Wasmtime GitHub notifications bot (Mar 12 2020 at 19:16):

peterhuene deleted a comment on Issue #1216:

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Wasmtime GitHub notifications bot (Mar 14 2020 at 00:08):

iximeow commented on Issue #1216:

Nudging this again as I think this is as good as this fix can get without getting into the weeds on stack layout details.

I have three(ish) issues to open assuming a :+1: :

[ ] Use of an F64 type instead of the more accurate F64x2 for callee-save FPRs, which _works_ but just isn't fully expressive of intent. See here

[ ] Fix how Cranelift lays out Fastcall stacks to avoid the 240-byte stack frame limit when using unwind information and callee-save XMM registers. See here for conversation and here for a test I've had to disable as a consequence.

[ ] Might not be worth a tracking issue, but there are two TODO's contingent on an encoding existing that would result in changes here after this lands.

Wasmtime GitHub notifications bot (Mar 17 2020 at 10:52):

github-actions[bot] commented on Issue #1216:

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Wasmtime GitHub notifications bot (Mar 26 2020 at 21:03):

iximeow commented on Issue #1216:

Pardon the rebase, just want to get this on a more recent master so as to pick up a fix for nightly builds failing in CI.

Wasmtime GitHub notifications bot (Mar 27 2020 at 10:17):

bjorn3 commented on Issue #1216:

@iximeow I think you forgot to push :)

Wasmtime GitHub notifications bot (Mar 27 2020 at 17:58):

iximeow commented on Issue #1216:

@bjorn3 even worse, I'd pushed to the wrong remote. Thanks for the heads up!

Wasmtime GitHub notifications bot (Mar 31 2020 at 02:14):

peterhuene commented on Issue #1216:

It looks like there's at least a few more tests to disable due to the frame size limitation this adds to functions using Windows x64 calling convention.

Wasmtime GitHub notifications bot (Apr 03 2020 at 17:50):

iximeow commented on Issue #1216:

it passes :tada:

GitHub appears to believe that 3be2d1c doesn't exist, so I pushed an empty commit (ea9f77a) to fool CI into running after yesterday's availability issues. After ignoring more tests, it's green again 🥴

Wasmtime GitHub notifications bot (Apr 03 2020 at 21:56):

peterhuene commented on Issue #1216:

@iximeow I'll review this soon and if everyone signs off, I think we should merge this before my unwind refactoring changes. I can easily update that PR to integrate this PR's changes to save the FPRs in the windows unwind info.

Wasmtime GitHub notifications bot (Apr 06 2020 at 18:47):

bjorn3 commented on Issue #1216:

We probably want @bjorn3 or another core cranelift maintainer to sign off as well.

I am actually not a maintainer. :)

Wasmtime GitHub notifications bot (Apr 06 2020 at 19:07):

peterhuene commented on Issue #1216:

:scream: my apologies, although your review is obviously always appreciated :) I'm not actually a core cranelift maintainer either, so I'm more comfortable when others sign off on bits I haven't been directly involved in.

Wasmtime GitHub notifications bot (Apr 06 2020 at 19:20):

bjorn3 commented on Issue #1216:

:scream: my apologies, although your review is obviously always appreciated :)

You are not the first to think I am a maintainer of a project. :) I often review PR's on projects I am (slightly) interested in. And sometimes the PR author assumes I am a maintainer.

Wasmtime GitHub notifications bot (Apr 06 2020 at 19:56):

peterhuene commented on Issue #1216:

I'll ping @bnjbvr for the core maintainer sign-off, then.

Wasmtime GitHub notifications bot (Apr 06 2020 at 23:42):

iximeow edited a comment on Issue #1216:

Nudging this again as I think this is as good as this fix can get without getting into the weeds on stack layout details.

I have three(ish) issues to open assuming a :+1: :

[ ] Use of an F64 type instead of the more accurate F64x2 for callee-save FPRs, which _works_ but just isn't fully expressive of intent. See here

[x] Fix how Cranelift lays out Fastcall stacks to avoid the 240-byte stack frame limit when using unwind information and callee-save XMM registers. See here for conversation and here for a test I've had to disable as a consequence.

[ ] Might not be worth a tracking issue, but there are two TODO's contingent on an encoding existing that would result in changes here after this lands.

Wasmtime GitHub notifications bot (Apr 09 2020 at 20:59):

github-actions[bot] commented on Issue #1216:

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Wasmtime GitHub notifications bot (Apr 10 2020 at 16:50):

iximeow commented on Issue #1216:

I had to force push to rebase and fix a merge conflict that crept in. Unwind-producing functions are Result-y, which of course resulted in some Wasmtime changes as well. Given the wider scope, I'd like one last +1 before clicking the tempting green button :)

Wasmtime GitHub notifications bot (Apr 10 2020 at 20:45):

iximeow edited a comment on Issue #1216:

Nudging this again as I think this is as good as this fix can get without getting into the weeds on stack layout details.

I have three(ish) issues to open assuming a :+1: :

[x] Use of an F64 type instead of the more accurate F64x2 for callee-save FPRs, which _works_ but just isn't fully expressive of intent. See here

[x] Fix how Cranelift lays out Fastcall stacks to avoid the 240-byte stack frame limit when using unwind information and callee-save XMM registers. See here for conversation and here for a test I've had to disable as a consequence.

[ ] Might not be worth a tracking issue, but there are two TODO's contingent on an encoding existing that would result in changes here after this lands.

Wasmtime GitHub notifications bot (Apr 10 2020 at 20:57):

iximeow edited a comment on Issue #1216:

Nudging this again as I think this is as good as this fix can get without getting into the weeds on stack layout details.

I have three(ish) issues to open assuming a :+1: :

[x] Use of an F64 type instead of the more accurate F64x2 for callee-save FPRs, which _works_ but just isn't fully expressive of intent. See here

[x] Fix how Cranelift lays out Fastcall stacks to avoid the 240-byte stack frame limit when using unwind information and callee-save XMM registers. See here for conversation and here for a test I've had to disable as a consequence.

[x] Might not be worth a tracking issue, but there are two TODO's contingent on an encoding existing that would result in changes here after this lands.

Wasmtime GitHub notifications bot (Apr 10 2020 at 23:14):

peterhuene commented on Issue #1216:

:tada: thanks for fixing this @iximeow! :tada: I realize it was a slog of a PR.

Now I get to merge these changes in to my refactoring PR and we'll see about prioritizing the fixing of the stack layout of the register saves :smile:

Wasmtime GitHub notifications bot (Apr 15 2020 at 07:26):

hrydgard commented on Issue #1216:

Awesome, thanks for getting this done!

Last updated: Dec 23 2024 at 13:07 UTC