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GH-119726: Deduplicate JIT trampolines for out-of-range jumps (GH-120250)

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Diego Russo 2024-06-19 02:27:02 +01:00 committed by GitHub
parent 07daaf1ce1
commit a0dce37895
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2 changed files with 17 additions and 4 deletions
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1
Misc/NEWS.d/next/Core and Builtins/2024-06-07-22-54-15.gh-issue-119726.D9EE-o.rst Normal file
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@ -0,0 +1 @@
JIT: Re-use trampolines on AArch64 when creating stencils. Patch by Diego Russo

20
Tools/jit/_stencils.py
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@ -181,6 +181,7 @@ class Stencil:
body: bytearray = dataclasses.field(default_factory=bytearray, init=False)
holes: list[Hole] = dataclasses.field(default_factory=list, init=False)
disassembly: list[str] = dataclasses.field(default_factory=list, init=False)
trampolines: dict[str, int] = dataclasses.field(default_factory=dict, init=False)
def pad(self, alignment: int) -> None:
"""Pad the stencil to the given alignment."""
@ -189,14 +190,25 @@ class Stencil:
self.disassembly.append(f"{offset:x}: {' '.join(['00'] * padding)}")
self.body.extend([0] * padding)
def emit_aarch64_trampoline(self, hole: Hole) -> None:
def emit_aarch64_trampoline(self, hole: Hole, alignment: int) -> None:
"""Even with the large code model, AArch64 Linux insists on 28-bit jumps."""
base = len(self.body)
assert hole.symbol is not None
reuse_trampoline = hole.symbol in self.trampolines
if reuse_trampoline:
# Re-use the base address of the previously created trampoline
base = self.trampolines[hole.symbol]
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)
if reuse_trampoline:
return
self.disassembly += [
f"{base + 4 * 0:x}: d2800008 mov x8, #0x0",
f"{base + 4 * 0:016x}: R_AARCH64_MOVW_UABS_G0_NC {hole.symbol}",
@ -225,6 +237,7 @@ class Stencil:
]
):
self.holes.append(hole.replace(offset=base + 4 * i, kind=kind))
self.trampolines[hole.symbol] = base
def remove_jump(self, *, alignment: int = 1) -> None:
"""Remove a zero-length continuation jump, if it exists."""
@ -300,8 +313,7 @@ class StencilGroup:
in {"R_AARCH64_CALL26", "R_AARCH64_JUMP26", "ARM64_RELOC_BRANCH26"}
and hole.value is HoleValue.ZERO
):
self.code.pad(alignment)
self.code.emit_aarch64_trampoline(hole)
self.code.emit_aarch64_trampoline(hole, alignment)
self.code.holes.remove(hole)
self.code.remove_jump(alignment=alignment)
self.code.pad(alignment)