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gh-119726: emit AArch64 trampolines in the data section #121280

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merged 2 commits into from
Jul 3, 2024
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gh-119726: emit AArch64 trampolines in the data section #121280

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gh-119726: emit AArch64 trampolines in the data section
diegorusso Jun 25, 2024
13e5a2f
Update Misc/NEWS.d/next/Core and Builtins/2024-06-28-18-34-49.gh-issu…
diegorusso Jul 3, 2024
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2024-06-28-18-34-49.gh-issue-119726.Fjv_Ab.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Optimize code layout for calls to C functions from the JIT on AArch64.
Patch by Diego Russo.
14 changes: 6 additions & 8 deletions Tools/jit/_stencils.py
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Expand Up @@ -184,7 +184,7 @@ def pad(self, alignment: int) -> None:
self.disassembly.append(f"{offset:x}: {' '.join(['00'] * padding)}")
self.body.extend([0] * padding)

def emit_aarch64_trampoline(self, hole: Hole, alignment: int) -> None:
def emit_aarch64_trampoline(self, hole: Hole, alignment: int) -> Hole:
"""Even with the large code model, AArch64 Linux insists on 28-bit jumps."""
assert hole.symbol is not None
reuse_trampoline = hole.symbol in self.trampolines
Expand All @@ -194,14 +194,10 @@ def emit_aarch64_trampoline(self, hole: Hole, alignment: int) -> None:
else:
self.pad(alignment)
base = len(self.body)
where = slice(hole.offset, hole.offset + 4)
instruction = int.from_bytes(self.body[where], sys.byteorder)
instruction &= 0xFC000000
instruction |= ((base - hole.offset) >> 2) & 0x03FFFFFF
self.body[where] = instruction.to_bytes(4, sys.byteorder)
new_hole = hole.replace(addend=base, symbol=None, value=HoleValue.DATA)
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This is so much nicer!


if reuse_trampoline:
return
return new_hole

self.disassembly += [
f"{base + 4 * 0:x}: 58000048 ldr x8, 8",
Expand All @@ -219,6 +215,7 @@ def emit_aarch64_trampoline(self, hole: Hole, alignment: int) -> None:
self.body.extend(code)
self.holes.append(hole.replace(offset=base + 8, kind="R_AARCH64_ABS64"))
self.trampolines[hole.symbol] = base
return new_hole

def remove_jump(self, *, alignment: int = 1) -> None:
"""Remove a zero-length continuation jump, if it exists."""
Expand Down Expand Up @@ -294,8 +291,9 @@ def process_relocations(self, *, alignment: int = 1) -> None:
in {"R_AARCH64_CALL26", "R_AARCH64_JUMP26", "ARM64_RELOC_BRANCH26"}
and hole.value is HoleValue.ZERO
):
self.code.emit_aarch64_trampoline(hole, alignment)
new_hole = self.data.emit_aarch64_trampoline(hole, alignment)
self.code.holes.remove(hole)
self.code.holes.append(new_hole)
self.code.remove_jump(alignment=alignment)
self.code.pad(alignment)
self.data.pad(8)
Expand Down
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