62 lines
2.7 KiB
ArmAsm
62 lines
2.7 KiB
ArmAsm
// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: BSD-3-Clause
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#include "textflag.h"
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// ABI-checking trampoline for riscv64. Sets a sentinel value in the
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// register the Go ABI fixes across calls before entering the JIT function
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// and checks whether it survived on return.
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//
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// The return trampoline (leaveJITCheckedRaw) is a raw TEXT symbol with no
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// Go function declaration, so the toolchain does NOT interpose an
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// ABIInternal wrapper — the JIT function RETs directly into the check
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// code, which sees the registers exactly as the function left them.
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//
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// Go ABI on riscv64 guarantees:
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// - X27 holds the goroutine pointer (g) and must survive across any
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// call. Go keeps no hardware frame pointer on riscv64. The assembler
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// spells this register "g"; X27 is not accepted.
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// Sentinel value chosen to be unlikely in normal execution.
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#define SENTINEL_G 0x0BADF00DDEADBEEF
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// GLOBL holding the raw address of the leave trampoline, read by Go.
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GLOBL ·leaveCheckedPtr(SB), NOPTR, $8
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DATA ·leaveCheckedPtr(SB)/8, $·leaveJITCheckedRaw(SB)
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// func enterJITChecked(fn uintptr, stack uintptr)
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// Sets a sentinel in g (X27), switches to the prepared stack and jumps to
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// fn. The prepared stack's first word must be the address of
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// leaveJITCheckedRaw (read from leaveCheckedPtr). Only X5 and X6 are used
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// as scratch: caller-saved, and X27 is not among them.
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TEXT ·enterJITChecked(SB), NOSPLIT, $0-16
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MOV fn+0(FP), X5 // target function address (T0)
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MOV X1, savedRA(SB) // save return address
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MOV X2, savedSP(SB) // save Go stack pointer
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MOV $SENTINEL_G, g // sentinel in g
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MOV stack+8(FP), X6 // load prepared stack pointer (T1)
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LD 0(X6), X1 // load leaveJITCheckedRaw into RA
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ADD $8, X6, X6 // advance past the return slot
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MOV X6, X2 // switch to prepared stack (SP)
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JALR X0, 0(X5) // jump to JIT function
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// leaveJITCheckedRaw is the raw return trampoline. It has NO Go function
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// declaration, so no ABIInternal wrapper is generated — the JIT function's
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// RET lands here directly, seeing g exactly as the function left it. It
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// checks the sentinel, records violations in abiResult, then restores the
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// Go stack and returns.
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TEXT ·leaveJITCheckedRaw(SB), NOSPLIT, $0-0
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// Check g against the sentinel.
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MOV $SENTINEL_G, X6
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BEQ g, X6, g_ok
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MOV ·abiResult(SB), X7
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MOV $2, X5
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OR X5, X7, X7
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MOV X7, ·abiResult(SB)
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g_ok:
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MOV savedSP(SB), X6 // restore Go stack pointer
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MOV X6, X2
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MOV savedRA(SB), X1 // restore return address
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JALR X0, 0(X1) // return to Go caller
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