1346a2d020
Adds examples/1655-platform-asm-callback-into-sx.sx: a global-asm trampoline (_caller) that `bl _cb` back into an `export`ed sx function. Demonstrates the sx → asm → sx round trip and that `export` (external linkage + stable C symbol + C ABI) is what makes the callback symbol resolvable — `callconv(.c)` alone leaves it internal and it DCE's away. Runs under the JIT on aarch64-macos (→ 42); ir-only elsewhere. Locks current behavior; no compiler change.
36 lines
1.4 KiB
Plaintext
36 lines
1.4 KiB
Plaintext
// ASM stream — the round trip: sx → asm → sx. A global-asm routine (`_caller`)
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// CALLS BACK into an sx function (`cb`) by its symbol, then returns. For the asm
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// `bl _cb` to resolve, the sx callback needs EXTERNAL LINKAGE and a stable C
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// symbol — that is exactly what `export` provides (it also implies the C ABI, so
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// no hidden context parameter). `callconv(.c)` alone is NOT enough: it sets the
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// ABI but leaves the function `internal`, so it is dead-code-eliminated (nothing
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// in the IR references it — the `bl` is opaque to the optimizer) and `_cb` is
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// undefined at link. macOS gives `export "cb"` the symbol `_cb` (leading
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// underscore), which the template references. aarch64-macos-pinned; runs under
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// the JIT here (sx run), ir-only elsewhere.
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// The sx callback — `export` gives it external linkage + the `_cb` symbol + C ABI.
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cb :: (n: i64) -> i64 export "cb" {
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return n + 1;
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}
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// A global-asm trampoline that calls back into `cb`. It saves/restores the link
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// register (x30) around the `bl` — it was itself reached via `bl`, so the return
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// address must survive the nested call.
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asm {
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#string ASM
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.global _caller
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_caller:
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stp x29, x30, [sp, #-16]!
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bl _cb // x0 = cb(x0) — back into sx
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ldp x29, x30, [sp], #16
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ret
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ASM,
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};
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caller :: (n: i64) -> i64 extern;
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main :: () -> i64 {
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return caller(41); // sx main → asm caller → bl _cb → sx cb → 42
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}
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