fork.c

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#include <core/system.h>
#include <core/string.h>
#include <core/arch.h>
#include <sys/proc.h>
#include <sys/sched.h>
 
#include <aquila/errno.h>
 
struct aarch64_thread *aarch64_thread_new(void);
 
/*
 * Sets up the child's thread of a `fork()`: its kernel stack, its saved
 * registers (its parent's), and its FP/SIMD state.
 */
int arch_proc_fork(struct thread *thread, struct proc *fork)
{
    struct aarch64_thread *parch = thread->arch;
    struct aarch64_thread *farch = aarch64_thread_new();
 
    if (!farch)
        return -ENOMEM;
 
    /* a copy of the fork system call's registers, at the top of its stack
     * (where user mode's next exception lands) */
    struct aarch64_regs *regs = (struct aarch64_regs *) (farch->kstack - sizeof(struct aarch64_regs));
    *regs = *parch->regs;
    farch->regs = regs;
 
    /* when it's first chosen, it starts at aarch64_fork_return
     * (cpu/vectors.S), which returns to user mode from that frame */
    extern void aarch64_fork_return(void);
    farch->ctx.lr = (uintptr_t) aarch64_fork_return;
    farch->ctx.sp = (uintptr_t) regs;
    farch->ctx.fp = 0;
 
    /* its FP/SIMD registers are its parent's */
    if (aarch64_fpsimd_fork(thread, farch)) {
        kfree((void *) farch->kstack_base);
        kfree(farch);
        return -ENOMEM;
    }
 
    struct thread *fthread = (struct thread *) fork->threads.head->value;
    fthread->arch = farch;
 
    return 0;
}