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(sys/i386/i386/machdep.c) ----------------------------------- setidt(IDT_SYSCALL, &IDTVEC(int0x80_syscall), SDT_SYS386TGT, SEL_UPL, GSEL(GCODE_SEL, SEL_KPL)); ----------------------------------- |
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(sys/i386/include/segments.h) --------------------------------- #define IDT_SYSCALL 0x80 /* System Call Interrupt Vector */ #define SDT_SYS386TGT 15 /* system 386 trap gate */ #define SEL_UPL 3 /* user priority level */ #define GSEL(s,r) (((s)<<3) | r) /* a global selector */ #define GCODE_SEL 1 /* Kernel Code Descriptor */ #define SEL_KPL 0 /* kernel priority level */ ---------------------------------- |
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(sys/i386/i386/machdep.c) ----------------------------------- void setidt(idx, func, typ, dpl, selec) int idx; inthand_t *func; int typ; int dpl; int selec; { struct gate_descriptor *ip; ip = idt + idx; ip->gd_looffset = (int)func; ip->gd_selector = selec; ip->gd_stkcpy = 0; ip->gd_xx = 0; ip->gd_type = typ; ip->gd_dpl = dpl; ip->gd_p = 1; ip->gd_hioffset = ((int)func)>>16 ; } ------------------------------------ |
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void syscall(frame) struct trapframe frame; |
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/* * Exception/Trap Stack Frame */ struct trapframe { int tf_fs; int tf_es; int tf_ds; int tf_edi; int tf_esi; int tf_ebp; int tf_isp; int tf_ebx; int tf_edx; int tf_ecx; int tf_eax; int tf_trapno; /* below portion defined in 386 hardware */ int tf_err; int tf_eip; int tf_cs; int tf_eflags; /* below only when crossing rings (e.g. user to kernel) */ int tf_esp; int tf_ss; }; |
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/* * Call gate entry for FreeBSD ELF and Linux/NetBSD syscall (int 0x80) * * Even though the name says 'int0x80', this is actually a TGT (trap gate) * rather then an IGT (interrupt gate). Thus interrupts are enabled on * entry just as they are for a normal syscall. */ SUPERALIGN_TEXT IDTVEC(int0x80_syscall) pushl $2 /* sizeof "int 0x80" */ |
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subl $4,%esp /* skip over tf_trapno */ pushal pushl %ds pushl %es pushl %fs |
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mov $KDSEL,%ax /* switch to kernel segments */ mov %ax,%ds mov %ax,%es mov $KPSEL,%ax mov %ax,%fs |
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FAKE_MCOUNT(13*4(%esp)) call syscall MEXITCOUNT jmp doreti |
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/* * syscall - system call request C handler * * A system call is essentially treated as a trap. */ void syscall(frame) struct trapframe frame; { caddr_t params; struct sysent *callp; struct thread *td = curthread; struct proc *p = td->td_proc; register_t orig_tf_eflags; u_int sticks; int error; int narg; int args[8]; u_int code; /* * note: PCPU_LAZY_INC() can only be used if we can afford * occassional inaccuracy in the count. */ PCPU_LAZY_INC(cnt.v_syscall); #ifdef DIAGNOSTIC if (ISPL(frame.tf_cs) != SEL_UPL) { mtx_lock(&Giant); /* try to stabilize the system XXX */ panic("syscall"); /* NOT REACHED */ mtx_unlock(&Giant); } #endif sticks = td->td_sticks; td->td_frame = &frame; if (td->td_ucred != p->p_ucred) cred_update_thread(td); |
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if (p->p_flag & P_SA) thread_user_enter(p, td); |
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(sys/sys/proc.h) #define P_SA 0x08000 /* Using scheduler activations. */ |
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params = (caddr_t)frame.tf_esp + sizeof(int); code = frame.tf_eax; |
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orig_tf_eflags = frame.tf_eflags; if (p->p_sysent->sv_prepsyscall) { /* * The prep code is MP aware. */ (*p->p_sysent->sv_prepsyscall)(&frame, args, &code, ¶ms); |
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} else { /* * Need to check if this is a 32 bit or 64 bit syscall. * fuword is MP aware. */ if (code == SYS_syscall) { /* * Code is first argument, followed by actual args. */ code = fuword(params); params += sizeof(int); } else if (code == SYS___syscall) { /* * Like syscall, but code is a quad, so as to maintain * quad alignment for the rest of the arguments. */ code = fuword(params); params += sizeof(quad_t); } } |
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if (p->p_sysent->sv_mask) code &= p->p_sysent->sv_mask; |
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if ( code >= p->p_sysent->sv_size) callp = &p->p_sysent->sv_table[0]; else callp = &p->p_sysent->sv_table[_code]; |
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narg = callp->sy_narg & SYF_ARGMASK; |
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/* * copyin and the ktrsyscall()/ktrsysret() code is MP-aware */ if (params != NULL && narg != 0) error = copyin(params, (caddr_t)args, (u_int)(narg * sizeof(int))); else error = 0; |
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#ifdef KTRACE if (KTRPOINT(td, KTR_SYSCALL)) ktrsyscall(code, narg, args); #endif /* * Try to run the syscall without Giant if the syscall * is MP safe. */ if ((callp->sy_narg & SYF_MPSAFE) == 0) mtx_lock(&Giant); |
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if (error == 0) { td->td_retval[0] = 0; td->td_retval[1] = frame.tf_edx; STOPEVENT(p, S_SCE, narg); PTRACESTOP_SC(p, td, S_PT_SCE); error = (*callp->sy_call)(td, args); } |
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switch (error) { case 0: frame.tf_eax = td->td_retval[0]; frame.tf_edx = td->td_retval[1]; frame.tf_eflags &= ~PSL_C; break; |
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case ERESTART: /* * Reconstruct pc, assuming lcall $X,y is 7 bytes, * int 0x80 is 2 bytes. We saved this in tf_err. */ frame.tf_eip -= frame.tf_err; break; |
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case EJUSTRETURN: break; default: if (p->p_sysent->sv_errsize) { if (error >= p->p_sysent->sv_errsize) error = -1; /* XXX */ else error = p->p_sysent->sv_errtbl[error]; } frame.tf_eax = error; frame.tf_eflags |= PSL_C; break; } |
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/* * Release Giant if we previously set it. */ if ((callp->sy_narg & SYF_MPSAFE) == 0) mtx_unlock(&Giant); |
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/* * Traced syscall. */ if ((orig_tf_eflags & PSL_T) && !(orig_tf_eflags & PSL_VM)) { frame.tf_eflags &= ~PSL_T; trapsignal(td, SIGTRAP, 0); } |
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/* * Handle reschedule and other end-of-syscall issues */ userret(td, &frame, sticks); |
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#ifdef KTRACE if (KTRPOINT(td, KTR_SYSRET)) ktrsysret(code, error, td->td_retval[0]); #endif /* * This works because errno is findable through the * register set. If we ever support an emulation where this * is not the case, this code will need to be revisited. */ STOPEVENT(p, S_SCX, code); PTRACESTOP_SC(p, td, S_PT_SCX); #ifdef DIAGNOSTIC cred_free_thread(td); #endif WITNESS_WARN(WARN_PANIC, NULL, "System call %s returning", (code >= 0 && code < SYS_MAXSYSCALL) ? syscallnames[_code] : "???"); mtx_assert(&sched_lock, MA_NOTOWNED); mtx_assert(&Giant, MA_NOTOWNED); } |
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/* * Define the code needed before returning to user mode, for * trap and syscall. * * MPSAFE */ void userret(td, frame, oticks) struct thread *td; struct trapframe *frame; u_int oticks; { struct proc *p = td->td_proc; CTR3(KTR_SYSC, "userret: thread %p (pid %d, %s)", td, p->p_pid, p->p_comm); #ifdef INVARIANTS /* Check that we called signotify() enough. */ PROC_LOCK(p); mtx_lock_spin(&sched_lock); if (SIGPENDING(td) && ((td->td_flags & TDF_NEEDSIGCHK) == 0 || (td->td_flags & TDF_ASTPENDING) == 0)) printf("failed to set signal flags properly for ast()\n"); mtx_unlock_spin(&sched_lock); PROC_UNLOCK(p); #endif /* * Let the scheduler adjust our priority etc. */ sched_userret(td); |
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/* * We need to check to see if we have to exit or wait due to a * single threading requirement or some other STOP condition. * Don't bother doing all the work if the stop bits are not set * at this time.. If we miss it, we miss it.. no big deal. */ if (P_SHOULDSTOP(p)) { PROC_LOCK(p); thread_suspend_check(0); /* Can suspend or kill */ PROC_UNLOCK(p); } |
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/* * Do special thread processing, e.g. upcall tweaking and such. */ if (p->p_flag & P_SA) { thread_userret(td, frame); } |
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/* * Charge system time if profiling. */ if (p->p_flag & P_PROFIL) { quad_t ticks; mtx_lock_spin(&sched_lock); ticks = td->td_sticks - oticks; mtx_unlock_spin(&sched_lock); addupc_task(td, TRAPF_PC(frame), (u_int)ticks * psratio); } } |
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