/**************************************************************************** * arch/arm/src/common/up_vfork.c * * Copyright (C) 2013 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. Neither the name NuttX nor the names of its contributors may be * used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include #include #include #include "up_vfork.h" #include "os_internal.h" /**************************************************************************** * Pre-processor Definitions ****************************************************************************/ /* ARM requires at least a 4-byte stack alignment. For use with EABI and * floating point, the stack must be aligned to 8-byte addresses. */ #ifndef CONFIG_STACK_ALIGNMENT /* The symbol __ARM_EABI__ is defined by GCC if EABI is being used. If you * are not using GCC, make sure that CONFIG_STACK_ALIGNMENT is set correctly! */ # ifdef __ARM_EABI__ # define CONFIG_STACK_ALIGNMENT 8 # else # define CONFIG_STACK_ALIGNMENT 4 # endif #endif /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: up_vfork * * Description: * The vfork() function has the same effect as fork(), except that the * behavior is undefined if the process created by vfork() either modifies * any data other than a variable of type pid_t used to store the return * value from vfork(), or returns from the function in which vfork() was * called, or calls any other function before successfully calling _exit() * or one of the exec family of functions. * * The overall sequence is: * * 1) User code calls vfork(). vfork() collects context information and * transfers control up up_vfork(). * 2) up_vfork()and calls task_vforksetup(). * 3) task_vforksetup() allocates and configures the child task's TCB. This * consists of: * - Allocation of the child task's TCB. * - Initialization of file descriptors and streams * - Configuration of environment variables * - Setup the intput parameters for the task. * - Initialization of the TCB (including call to up_initial_state() * 4) up_vfork() provides any additional operating context. up_vfork must: * - Allocate and initialize the stack * - Initialize special values in any CPU registers that were not * already configured by up_initial_state() * 5) up_vfork() then calls task_vforkstart() * 6) task_vforkstart() then executes the child thread. * * task_vforkabort() may be called if an error occurs between steps 3 and 6. * * Input Paremeters: * context - Caller context information saved by vfork() * * Return: * Upon successful completion, vfork() returns 0 to the child process and * returns the process ID of the child process to the parent process. * Otherwise, -1 is returned to the parent, no child process is created, * and errno is set to indicate the error. * ****************************************************************************/ pid_t up_vfork(const struct vfork_s *context) { struct tcb_s *parent = (FAR struct tcb_s *)g_readytorun.head; struct task_tcb_s *child; size_t stacksize; uint32_t newsp; uint32_t newfp; uint32_t stackutil; int ret; svdbg("r4:%08x r5:%08x r6:%08x r7:%08x\n", context->r4, context->r5, context->r6, context->r7); svdbg("r8:%08x r9:%08x r10:%08x\n", context->r8, context->r9, context->r10); svdbg("fp:%08x sp:%08x lr:%08x\n", context->fp, context->sp, context->lr); /* Allocate and initialize a TCB for the child task. */ child = task_vforksetup((start_t)(context->lr & ~1)); if (!child) { sdbg("task_vforksetup failed\n"); return (pid_t)ERROR; } svdbg("Parent=%p Child=%p\n", parent, child); /* Get the size of the parent task's stack. Due to alignment operations, * the adjusted stack size may be smaller than the stack size originally * requrested. */ stacksize = parent->adj_stack_size + CONFIG_STACK_ALIGNMENT - 1; /* Allocate the stack for the TCB */ ret = up_create_stack((FAR struct tcb_s *)child, stacksize); if (ret != OK) { sdbg("up_create_stack failed: %d\n", ret); task_vforkabort(child, -ret); return (pid_t)ERROR; } /* How much of the parent's stack was utilized? The ARM uses * a push-down stack so that the current stack pointer should * be lower than the initial, adjusted stack pointer. The * stack usage should be the difference between those two. */ DEBUGASSERT((uint32_t)parent->adj_stack_ptr > context->sp); stackutil = (uint32_t)parent->adj_stack_ptr - context->sp; svdbg("stacksize:%d stackutil:%d\n", stacksize, stackutil); /* Make some feeble effort to perserve the stack contents. This is * feeble because the stack surely contains invalid pointers and other * content that will not work in the child context. However, if the * user follows all of the caveats of vfor() usage, even this feeble * effort is overkill. */ newsp = (uint32_t)child->cmn.adj_stack_ptr - stackutil; memcpy((void *)newsp, (const void *)context->sp, stackutil); /* Was there a frame pointer in place before? */ if (context->fp <= (uint32_t)parent->adj_stack_ptr && context->fp >= (uint32_t)parent->adj_stack_ptr - stacksize) { uint32_t frameutil = (uint32_t)parent->adj_stack_ptr - context->fp; newfp = (uint32_t)child->cmn.adj_stack_ptr - frameutil; } else { newfp = context->fp; } svdbg("Old stack base:%08x SP:%08x FP:%08x\n", parent->adj_stack_ptr, context->sp, context->fp); svdbg("New stack base:%08x SP:%08x FP:%08x\n", child->cmn.adj_stack_ptr, newsp, newfp); /* Update the stack pointer, frame pointer, and volatile registers. When * the child TCB was initialized, all of the values were set to zero. * up_initial_state() altered a few values, but the return value in R0 * should be cleared to zero, providing the indication to the newly started * child thread. */ child->cmn.xcp.regs[REG_R4] = context->r4; /* Volatile register r4 */ child->cmn.xcp.regs[REG_R5] = context->r5; /* Volatile register r5 */ child->cmn.xcp.regs[REG_R6] = context->r6; /* Volatile register r6 */ child->cmn.xcp.regs[REG_R7] = context->r7; /* Volatile register r7 */ child->cmn.xcp.regs[REG_R8] = context->r8; /* Volatile register r8 */ child->cmn.xcp.regs[REG_R9] = context->r9; /* Volatile register r9 */ child->cmn.xcp.regs[REG_R10] = context->r10; /* Volatile register r10 */ child->cmn.xcp.regs[REG_FP] = newfp; /* Frame pointer */ child->cmn.xcp.regs[REG_SP] = newsp; /* Stack pointer */ /* And, finally, start the child task. On a failure, task_vforkstart() * will discard the TCB by calling task_vforkabort(). */ return task_vforkstart(child); }