70ce288dc7
* Wasmtime: Add a pointer to `VMRuntimeLimits` in component contexts * Save exit Wasm FP and PC in component-to-host trampolines Fixes #4535 * Add comment about why we deref the trampoline's FP * Update some tests to use new `vmruntime_limits_*` methods
32 lines
1.3 KiB
Rust
32 lines
1.3 KiB
Rust
pub unsafe fn get_next_older_pc_from_fp(fp: usize) -> usize {
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// The calling convention always pushes the return pointer (aka the PC of
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// the next older frame) just before this frame.
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*(fp as *mut usize).offset(1)
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}
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// And the current frame pointer points to the next older frame pointer.
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pub const NEXT_OLDER_FP_FROM_FP_OFFSET: usize = 0;
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pub fn reached_entry_sp(fp: usize, first_wasm_sp: usize) -> bool {
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// When the FP is just below the SP (because we are in a function prologue
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// where the `call` pushed the return pointer, but the callee hasn't pushed
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// the frame pointer yet) we are done.
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fp == first_wasm_sp - 8
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}
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pub fn assert_entry_sp_is_aligned(sp: usize) {
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// The stack pointer should always be aligned to 16 bytes *except* inside
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// function prologues where the return PC is pushed to the stack but before
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// the old frame pointer has been saved to the stack via `push rbp`. And
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// this happens to be exactly where we are inside of our host-to-Wasm
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// trampoline that records the value of SP when we first enter
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// Wasm. Therefore, the SP should *always* be 8-byte aligned but *never*
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// 16-byte aligned.
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assert_eq!(sp % 8, 0);
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assert_eq!(sp % 16, 8);
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}
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pub fn assert_fp_is_aligned(fp: usize) {
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assert_eq!(fp % 16, 0, "stack should always be aligned to 16");
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}
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