Robert Allan JamesandClaude Sonnet 5
f790d0995e
Third stage of the preemptive context-switching plan. The real save/restore switch mechanism now exists -- the first time anything has ever executed on a VM's own native stack (Stage 1 allocated them, unused). New sk_vm_switch_to() (switch.S, one per arch) is an ordinary function call, not an interrupt -- so unlike Stage 0's trap frame, the ABI already covers every caller-saved register; only the callee-saved set needs explicit save/restore (amd64: rbx/rbp/r12-r15, no FP at all since SysV has no callee-saved XMM; aarch64: x19-x28/x29/x30 + d8-d15; riscv64: s0-s11/ra + fs0-fs11, FS-gated like Stage 0 but read once and reused for both halves within one call, since FS is genuine global CPU state, not part of what's switched). A sibling sk_vm_switch_prime() in the same file builds the synthetic first-entry frame, kept in assembly so the layout can never drift out of sync with sk_vm_switch_to() itself. New switch.c/switch.h: sk_vm_context_switch(from, to) handles first-entry priming vs. resuming a parked context, and updates registry state (new VM_STATE_SWITCHED_OUT, distinct from VM_STATE_STOPPED -- STOPPED means no live frame, this means the opposite). sk_vm_switch_entry() is the minimal permanent trampoline every freshly-entered VM lands in: no production behavior defined yet, so it just yields straight back to whoever switched to it, forever. Closes the confirmed unguarded-KILL UAF found during planning: capsule_vm_kill(), mama_word_kill(), and capsule_vm_kill_all_nonmama() all now refuse (or silently leak rather than free, on the cold-restart path where arch_cold_reset() wipes everything immediately after anyway) tearing down a switched-out VM. Side effect found, not built on purpose: the existing MSG-TICK idle-pump already filters on VM_STATE_LIVE, so it automatically stopped dispatching into a switched-out VM with zero changes needed there. Verified via a temporary SWITCH-TEST probe (boot-triggered, since nothing can type interactively into a foreground-only QEMU session) that round-tripped a sentinel through 5 real Hera<->Hermes switches on all 3 architectures: 5/5 rounds, 0 failures, clean continuation to ok>. Probe fully reverted after capture; kernel_main.c shows zero diff. Also: Makefile.starkernel's LOADER_EXTRA_SRCS/LOADER_ASM needed the new files added explicitly (this project's "loader" PE binary is the full running kernel, not a thin bootstrap stage), and aarch64's switch.S needed the same #ifndef _WIN32 guard around .hidden that isr.S already carries (aarch64's loader assembles via clang targeting a PE/COFF target with no .hidden equivalent) -- caught by a build failure, fixed. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_016UNhH1mhi52i6Qihh7ZV5S
52 lines
1.7 KiB
C
52 lines
1.7 KiB
C
/*
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StarForth — Steady-State Virtual Machine Runtime
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Copyright (c) 2023–2025 Robert A. James
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All rights reserved.
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This file is part of the StarForth project.
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Licensed under the StarForth License, Version 1.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at:
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https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
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This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
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express or implied, including but not limited to the warranties of
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merchantability, fitness for a particular purpose, and noninfringement.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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/**
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* switch.h - Cooperative VM context switch (FABRIC-3.md §XXVIII, Stage 2,
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* 2026-09-13).
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*
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* sk_vm_context_switch() suspends `from`'s execution exactly where it is
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* (mid-C-call-stack, on from's own native stack -- Stage 1) and resumes
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* `to` -- either for the first time ever (a synthesized initial frame,
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* entering sk_vm_switch_entry()) or exactly where `to` was itself last
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* switched out. Returns to the caller only once something later switches
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* back to `from` -- from from's own point of view, this call simply
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* takes a while to return, like any blocking call.
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*
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* Cooperative only: nothing here is interrupt-driven yet (that's Stage
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* 3), so this is safe to call only from ordinary FORTH word dispatch,
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* never from ISR context.
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*/
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#ifndef STARKERNEL_VM_SWITCH_H
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#define STARKERNEL_VM_SWITCH_H
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#ifdef __STARKERNEL__
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struct VM;
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int sk_vm_context_switch(struct VM *from, struct VM *to);
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#endif /* __STARKERNEL__ */
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#endif /* STARKERNEL_VM_SWITCH_H */
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