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Implement swapcontext() and makecontext()
This change introduces support for Linux-style uc_context manipulation that's fast and works well on all supported OSes and architectures. It also integrates with the Cosmpolitan runtime which can show backtraces comprised of multiple stacks and fibers. See the test and example code for further details. This will be used by Mold once it's been vendored
This commit is contained in:
Justine Tunney
parent
7ec84655b4
commit
197aa0d465
28 changed files with 617 additions and 355 deletions
129
libc/thread/makecontext.c
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129
libc/thread/makecontext.c
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@ -0,0 +1,129 @@
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/assert.h"
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#include "libc/calls/struct/ucontext.internal.h"
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#include "libc/calls/ucontext.h"
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#include "libc/nexgen32e/nexgen32e.h"
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#include "libc/nexgen32e/stackframe.h"
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#include "libc/runtime/runtime.h"
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#include "libc/stdalign.internal.h"
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#include "libc/str/str.h"
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#include "libc/thread/thread.h"
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struct Gadget {
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void (*func)();
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int args[6];
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};
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static void runcontext(struct Gadget *call, ucontext_t *link) {
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call->func(call->args[0], //
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call->args[1], //
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call->args[2], //
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call->args[3], //
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call->args[4], //
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call->args[5]);
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if (link) {
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setcontext(link);
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abort();
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} else {
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pthread_exit(0);
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}
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}
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/**
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* Creates coroutine gadget, e.g.
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*
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* ucontext_t uc;
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* getcontext(&uc);
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* uc.uc_link = 0;
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* uc.uc_stack.ss_sp = NewCosmoStack();
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* uc.uc_stack.ss_size = GetStackSize();
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* makecontext(&uc, exit, 1, 42);
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* setcontext(&uc);
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*
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* Is equivalent to:
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*
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* exit(42);
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*
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* @param uc stores processor state; the caller must:
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* 1. initialize it using getcontext()
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* 2. assign new value to `uc->uc_stack.ss_sp`
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* 3. use `uc->uc_link` to define successor context
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* @param func is the function to call when `uc` is activated;
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* when `func` returns control passes to the linked context
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* which if null will result in pthread_exit() being called
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* @param argc is number of `int` arguments for `func` (max 6)
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* @threadsafe
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*/
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void makecontext(ucontext_t *uc, void func(), int argc, ...) {
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int i;
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va_list va;
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uintptr_t sp;
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struct Gadget *call;
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struct StackFrame *sf;
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assert(argc <= 6u);
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// allocate call
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sp = (uintptr_t)uc->uc_stack.ss_sp;
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sp += uc->uc_stack.ss_size;
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sp -= sizeof(*call);
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sp &= -alignof(*call);
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call = (struct Gadget *)sp;
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// get arguments
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va_start(va, argc);
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call->func = func;
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for (i = 0; i < argc; ++i) {
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call->args[i] = va_arg(va, int);
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}
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va_end(va);
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// construct fake function call on new stack
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//
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// the location where getcontext() was called shall be the previous
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// entry in the backtrace when runcontext was called, e.g.
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//
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// 1000800bf160 423024 systemfive_linux+31
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// 1000800fff90 405299 abort+58
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// 1000800fffb0 40d98c runcontext+42
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// 1000800fffd0 40b308 makecontext_backtrace+20
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// 7fff22a7ff50 40c2d5 testlib_runtestcases+218
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// 7fff22a7ff90 40b1c3 testlib_runalltests+79
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// 7fff22a7ffa0 4038cb main+475
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// 7fff22a7ffe0 403cfb cosmo+69
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// 7fff22a7fff0 4034e2 _start+137
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//
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// is about what it should look like.
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sp &= -(sizeof(uintptr_t) * 2);
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#ifdef __x86__
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*(uintptr_t *)(sp -= sizeof(uintptr_t)) = uc->uc_mcontext.PC;
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#elif defined(__aarch64__)
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*(uintptr_t *)(sp -= sizeof(uintptr_t)) = uc->uc_mcontext.regs[30];
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*(uintptr_t *)(sp -= sizeof(uintptr_t)) = uc->uc_mcontext.regs[29];
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uc->uc_mcontext.BP = uc->uc_mcontext.SP;
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#else
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#error "unsupported architecture"
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#endif
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// program context
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uc->uc_mcontext.SP = sp;
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uc->uc_mcontext.PC = (uintptr_t)runcontext;
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uc->uc_mcontext.ARG0 = (uintptr_t)call;
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uc->uc_mcontext.ARG1 = (uintptr_t)uc->uc_link;
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}
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@ -26,13 +26,13 @@
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*
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* pthread_t id;
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* pthread_attr_t attr;
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* char *stk = _mapstack();
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* char *stk = NewCosmoStack();
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* pthread_attr_init(&attr);
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* pthread_attr_setstack(&attr, stk, GetStackSize());
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* pthread_create(&id, &attr, func, 0);
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* pthread_attr_destroy(&attr);
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* pthread_join(id, 0);
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* _freestack(stk);
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* FreeCosmoStack(stk);
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*
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* Your stack must have at least `PTHREAD_STACK_MIN` bytes, which
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* Cosmpolitan Libc defines as `GetStackSize()`. It's a link-time
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@ -44,7 +44,7 @@
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* (e.g. kprintf) assumes that stack sizes are two-powers and are
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* aligned to that two-power. Conformance isn't required since we
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* say caveat emptor to those who don't maintain these invariants
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* please consider using _mapstack() which always does it perfect
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* please consider using NewCosmoStack(), which is always perfect
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* or use `mmap(0, GetStackSize() << 1, ...)` for a bigger stack.
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*
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* Unlike pthread_attr_setstacksize(), this function permits just
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@ -117,7 +117,7 @@ int _spawn(int fun(void *, int), void *arg, struct spawn *opt_out_thread) {
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// we must use _mapstack() to allocate the stack because OpenBSD has
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// very strict requirements for what's allowed to be used for stacks
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if (!(th->stk = _mapstack())) {
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if (!(th->stk = NewCosmoStack())) {
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free(th->tls);
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return -1;
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}
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@ -132,7 +132,7 @@ int _spawn(int fun(void *, int), void *arg, struct spawn *opt_out_thread) {
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spawner, &th->ptid, __adj_tls(th->tib), &th->tib->tib_tid);
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if (rc) {
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errno = rc;
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_freestack(th->stk);
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FreeCosmoStack(th->stk);
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free(th->tls);
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return -1;
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}
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