1 /* 2 * Copyright (c) 2015 Matthew Dillon, All rights reserved. 3 * 4 * 1. Redistributions of source code must retain the above copyright 5 * notice, this list of conditions and the following disclaimer. 6 * 2. Redistributions in binary form must reproduce the above copyright 7 * notice, this list of conditions and the following disclaimer in 8 * the documentation and/or other materials provided with the 9 * distribution. 10 * 11 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 12 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 13 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 14 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 15 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 16 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 17 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 18 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 19 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 20 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 21 * SUCH DAMAGE. 22 */ 23 24 #include <sys/cdefs.h> 25 #include <sys/param.h> 26 #include <sys/signal.h> 27 #include <sys/ucontext.h> 28 29 #include <machine/frame.h> 30 #include <machine/tss.h> 31 #include <machine/segments.h> 32 33 #include <signal.h> 34 #include <errno.h> 35 #include <string.h> 36 #include <stdarg.h> 37 #include <stdlib.h> 38 #include <unistd.h> 39 40 /* Prototypes */ 41 42 void _makecontext_quick(ucontext_t *); 43 44 static void makectx_quick_wrapper(ucontext_t *ucp, uint64_t *stack_top); 45 46 /* 47 * makecontext_quick() associates a stack with a user thread context 48 * setup to execute a cofunc sequence. The caller only initializes the 49 * uc_stack.* fields, uc_cofunc, and uc_arg. This function will zero or 50 * initialize all other fields. Upon return the caller can optionally 51 * also initialize uc_link. 52 * 53 * These 'quick' calls do not mess with the signal mask and do not require 54 * kernel intervention. Scratch registers (including FP regs, which are also 55 * scratch registers) are not saved or restored. Cofunction loops also 56 * optimize cofunc call loops by not saving the register state when 57 * switching away to double performance. Of course, swapcontext_quick() 58 * still saves the register state. There is no getcontext_quick() call 59 * on purpose. 60 */ 61 void 62 _makecontext_quick(ucontext_t *ucp) 63 { 64 uint64_t *stack_top; 65 66 if (ucp == NULL) 67 return; 68 bzero(&ucp->uc_sigmask, sizeof(ucp->uc_sigmask)); 69 bzero(&ucp->uc_mcontext, sizeof(ucp->uc_mcontext)); 70 ucp->uc_link = NULL; 71 ucp->uc_mcontext.mc_len = sizeof(mcontext_t); 72 73 stack_top = 74 (uint64_t *)((char *)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size); 75 stack_top = (uint64_t *)((uint64_t)(stack_top) & ~63UL); 76 stack_top -= 1; 77 78 /* 79 * Set the machine context to point to the top of the 80 * stack and the program counter to the context start 81 * wrapper. Note that setcontext() pushes the return 82 * address onto the top of the stack, so allow for this 83 * by adjusting the stack downward 1 slot. Also set 84 * %rbp to point to the base of the stack where ucp 85 * is stored. 86 */ 87 ucp->uc_mcontext.mc_rdi = (register_t)ucp; 88 ucp->uc_mcontext.mc_rsi = (register_t)stack_top; 89 ucp->uc_mcontext.mc_rsp = (register_t)stack_top; 90 ucp->uc_mcontext.mc_rip = (register_t)makectx_quick_wrapper; 91 ucp->uc_mcontext.mc_ownedfp = _MC_FPOWNED_NONE; 92 ucp->uc_mcontext.mc_fpformat = _MC_FPFMT_NODEV; 93 ucp->uc_mcontext.mc_cs = GSEL(GUCODE_SEL, SEL_UPL); 94 ucp->uc_mcontext.mc_ss = GSEL(GUDATA_SEL, SEL_UPL); 95 } 96 97 __weak_reference(_makecontext_quick, makecontext_quick); 98 99 /* 100 * If the cofunc call returns set the context up to re-execute the 101 * wrapper if the linkages eventually link back to this ucp. The 102 * cofunc can also change uc_cofunc and uc_arg as it desires, allowing 103 * cofunctions to be optimally linked together. 104 */ 105 static void 106 makectx_quick_wrapper(ucontext_t *ucp, uint64_t *stack_top) 107 { 108 for (;;) { 109 ucp->uc_cofunc(ucp, ucp->uc_arg); 110 if (ucp->uc_link == ucp) 111 continue; 112 ucp->uc_mcontext.mc_rdi = (register_t)ucp; 113 ucp->uc_mcontext.mc_rsi = (register_t)stack_top; 114 ucp->uc_mcontext.mc_rsp = (register_t)stack_top; 115 ucp->uc_mcontext.mc_rip = (register_t)makectx_quick_wrapper; 116 if (ucp->uc_link) 117 setcontext_quick(ucp->uc_link); 118 exit(0); 119 } 120 } 121