This removes an existing dependency on the byteorder crate in favor of
using std equivalents directly.
While not an issue for wasmtime per se, cranelift is now part of the
critical path of building and testing Rust, and minimizing dependencies,
even small ones, can help reduce the time and bandwidth required.
This commit makes the following changes to unwind information generation in
Cranelift:
* Remove frame layout change implementation in favor of processing the prologue
and epilogue instructions when unwind information is requested. This also
means this work is no longer performed for Windows, which didn't utilize it.
It also helps simplify the prologue and epilogue generation code.
* Remove the unwind sink implementation that required each unwind information
to be represented in final form. For FDEs, this meant writing a
complete frame table per function, which wastes 20 bytes or so for each
function with duplicate CIEs. This also enables Cranelift users to collect the
unwind information and write it as a single frame table.
* For System V calling convention, the unwind information is no longer stored
in code memory (it's only a requirement for Windows ABI to do so). This allows
for more compact code memory for modules with a lot of functions.
* Deletes some duplicate code relating to frame table generation. Users can
now simply use gimli to create a frame table from each function's unwind
information.
Fixes#1181.
Preserve FPRs as required by the Windows fastcall calling convention.
This exposes an implementation limit due to Cranelift's approach to stack layout, which conflicts with expectations Windows makes in SEH layout - functions where the Cranelift user desires fastcall unwind information, that require preservation of an ABI-reserved FPR, that have a stack frame 240 bytes or larger, now produce an error when compiled. Several wasm spectests were disabled because they would trip this limit. This is a temporary constraint that should be fixed promptly.
Co-authored-by: bjorn3 <bjorn3@users.noreply.github.com>
This commit removes the dependency on `byteorder::ReadBytesExt`, which can't be
used from `no_std`, which is how we're building the `byteorder` crate.
The fix is to simply offset into the slice as needed rather than using a
`std::io::Cursor`.
Fixes#1225.
* Implement emitting Windows unwind information for fastcall functions.
This commit implements emitting Windows unwind information for x64 fastcall
calling convention functions.
The unwind information can be used to construct a Windows function table at
runtime for JIT'd code, enabling stack walking and unwinding by the operating
system.
* Address code review feedback.
This commit addresses code review feedback:
* Remove unnecessary unsafe code.
* Emit the unwind information always as little endian.
* Fix comments.
A dependency from cranelift-codegen to the byteorder crate was added.
The byteorder crate is a no-dependencies crate with a reasonable
abstraction for writing binary data for a specific endianness.
* Address code review feedback.
* Disable default features for the `byteorder` crate.
* Add a comment regarding the Windows ABI unwind code numerical values.
* Panic if we encounter a Windows function with a prologue greater than 256
bytes in size.
