Wasmtime GitHub notifications bot (Sep 23 2020 at 23:36): Wasmtime GitHub notifications bot (Sep 23 2020 at 23:36):cfallin opened PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 23 2020 at 23:36):cfallin requested bnjbvr for a review on PR #2223.
Wasmtime GitHub notifications bot (Sep 24 2020 at 12:33):bnjbvr submitted PR Review.
Wasmtime GitHub notifications bot (Sep 24 2020 at 16:38):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 24 2020 at 16:51):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 24 2020 at 17:11):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 24 2020 at 17:51):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
<!--
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Wasmtime GitHub notifications bot (Sep 25 2020 at 08:26):bnjbvr requested bnjbvr for a review on PR #2223.
Wasmtime GitHub notifications bot (Sep 25 2020 at 09:46):bnjbvr submitted PR Review.
Wasmtime GitHub notifications bot (Sep 29 2020 at 20:41):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 30 2020 at 08:37):bnjbvr submitted PR Review.
Wasmtime GitHub notifications bot (Sep 30 2020 at 08:37):bnjbvr submitted PR Review.
Wasmtime GitHub notifications bot (Sep 30 2020 at 08:37):bnjbvr created PR Review Comment:
Here (and in the aarch64 code), can you use a const value to represent the offset to the TLS? (Maybe precise in the comment "caller" TLS, too?)
A few questions for my own understanding of this solution compared to others:
- would it make sense to put this responsibility on the caller's side, just after the call site, in the baldrdash glue? It's already done for calls to imports, as far as i can tell: https://searchfox.org/mozilla-central/source/js/src/wasm/cranelift/src/wasm2clif.rs#1012
- could we mark the TLS reg as part of the callee-saved registers in the Baldrdash calling convention, and not do anything particular here for this register?
Wasmtime GitHub notifications bot (Sep 30 2020 at 21:43):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 30 2020 at 21:56):cfallin updated PR #2223 from baldrdash-2020 to main:
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.Note that this adds a new ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).Corresponds to patch on SpiderMonkey bug 1657802.
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Wasmtime GitHub notifications bot (Sep 30 2020 at 22:00):cfallin submitted PR Review.
Wasmtime GitHub notifications bot (Sep 30 2020 at 22:00):cfallin created PR Review Comment:
Done, thanks! A small point, but it's actually the callee TLS that we restore; my reading of the ABI document is that we're supposed to leave the TLS register value unchanged, i.e., it must be the same at exit as it is at entry, so that would be the callee value.
would it make sense to put this responsibility on the caller's side
I thought about this too, but I don't think this follows the ABI strictly, as (given the above) we must do the restoration before the return.
could we mark the TLS reg as part of the callee-saved registers
I considered this too, but tweaking the
RealRegUniverseconstruction to work properly with two optionally-allocatable registers (the pinned register and the TLS register) proved a bit too complex; the indices for registers would have to be dependent on the flags/calling convention. If we refactor this as we discussed a few days ago, then we might want to reconsider, but for now, it seems simpler just to restore the register.
Wasmtime GitHub notifications bot (Sep 30 2020 at 22:33):cfallin merged PR #2223.
Last updated: Nov 22 2024 at 16:03 UTC