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1.18.0
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AquilaOS documentation
How it works, and its code
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x86: signals, on the way back to user mode, and a handler's frame. More...
#include <core/system.h>#include <core/arch.h>#include <core/string.h>#include <cpu/cpu.h>#include <ds/hashmap.h>#include <mm/mm.h>#include <mm/pmap.h>#include <mm/vm.h>#include <sys/proc.h>#include <sys/sched.h>#include <sys/signal.h>#include <sys/uaccess.h>#include <aquila/syscall.h>Go to the source code of this file.
Data Structures | |
| struct | sigframe |
| A signal handler's frame, on the user stack. More... | |
Macros | |
| #define | REG_IP(r) |
| #define | REG_SP(r) |
| #define | REG_AX(r) |
| #define | REG_FLAGS(r) |
| #define | USER_FLAGS 0x00240DD5UL |
| #define | I386_ARGS 20 |
Functions | |
| static int | vm_page_eq (void *a, void *b) |
| Compares a page with an offset, for the sigcode object's hashmap. | |
| static struct vm_page * | sigcode_in (struct vm_object *vm_object, size_t off) |
| Makes the sigcode page, the first time a process touches it. | |
| int | arch_sigcode_map (struct proc *proc) |
| Maps the page with the code that calls sigreturn() (the sigcode) into a process's new address space. | |
| static void | deliver (struct x86_regs *r, int sig) |
| Makes the handler of sig run when the context r is returned to: writes its frame on the user stack, and points r at the handler. | |
| void | x86_return_to_user (struct x86_regs *r, int syscall) |
| Delivers the current process's pending signals on the way back to user mode: stops and default actions, a handler, and the restart (or EINTR) of a system call that a signal interrupted. | |
| void | arch_sigreturn (void) |
| Returns from a signal handler, for sigreturn(): restores the registers, the signal mask and the FPU state that the handler's frame saved. | |
Variables | |
| static const uint8_t | sigcode [] |
| static struct vm_pager | sigcode_pager |
| static struct vm_object | sigcode_object |
x86: signals, on the way back to user mode, and a handler's frame.
Every return to user mode (from a system call, an interrupt or an exception) goes through x86_return_to_user(). There the process takes its signals (signal_take(): stops, default actions), a system call that a signal interrupted is restarted or fails with EINTR, and a handler is made to run by rewriting the user context saved on the kernel stack. Signals come nowhere else, so the kernel never leaves anything halfway.
A handler's frame, on the user stack, is what the handler returns to (the sigcode page) and its arguments (in registers on x86_64), then a struct sigframe: the siginfo, the mask to restore, and the interrupted registers and FPU state.
The handler returns into the sigcode page, mapped in every process (SIGCODE_ADDR, shared, read and execute), which makes the sigreturn system call. It reads the frame back, checks its registers (user segments, no privileged flags), and restores the mask and the FPU state.
The frame is made in the kernel and written with copyout(), and read back with copyin(): a stack that isn't there is the process's fault (SIGSEGV), not the kernel's.
Definition in file signal.c.
| #define I386_ARGS 20 |
Definition at line 72 of file signal.c.
Referenced by arch_sigreturn(), and deliver().
| #define REG_AX | ( | r | ) |
| #define REG_FLAGS | ( | r | ) |
Definition at line 52 of file signal.c.
Referenced by arch_sigreturn(), and deliver().
| #define REG_IP | ( | r | ) |
Definition at line 49 of file signal.c.
Referenced by deliver(), and x86_return_to_user().
| #define REG_SP | ( | r | ) |
Definition at line 50 of file signal.c.
Referenced by arch_sigreturn(), and deliver().
| int arch_sigcode_map | ( | struct proc * | proc | ) |
Maps the page with the code that calls sigreturn() (the sigcode) into a process's new address space.
| proc | the process |
Definition at line 129 of file signal.c.
References arch_sigcode_map(), vm_entry::base, vm_entry::flags, kfree(), kmalloc(), M_ZERO, PAGE_SIZE, vm_object::pages, SIGCODE_ADDR, sigcode_object, vm_entry::size, vm_entry::vm_object, vm_object_incref(), vm_page_eq(), proc::vm_space, vm_space_insert(), and VM_URX.
| void arch_sigreturn | ( | void | ) |
Returns from a signal handler, for sigreturn(): restores the registers, the signal mask and the FPU state that the handler's frame saved.
A bad frame gets SIGSEGV.
Definition at line 291 of file signal.c.
References arch_sigreturn(), x86_regs::cs, curproc, curthread, sigframe::fpu, sigframe::fxsave, I386_ARGS, sigframe::mask, REG_FLAGS, REG_SP, sigframe::regs, x86_thread::regs, SIG_UNMASKABLE, signal_force(), x86_regs::ss, USER_FLAGS, X86_CS, X86_EFLAGS, x86_fpu_load_from(), and X86_SS.
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Makes the handler of sig run when the context r is returned to: writes its frame on the user stack, and points r at the handler.
Definition at line 157 of file signal.c.
References curproc, curthread, deliver(), thread::fault_addr, sigframe::fpu, sigframe::fxsave, I386_ARGS, sigframe::info, sigframe::mask, memset(), x86_regs::rdi, x86_regs::rdx, REG_FLAGS, REG_IP, REG_SP, sigframe::regs, x86_regs::rsi, SIG_DFL, thread::sig_oldmask, thread::sig_oldmask_set, SIG_UNMASKABLE, proc::sigaction, SIGCODE_ADDR, proc::sigmask, signal_exit(), USER_FLAGS, X86_EFLAGS, x86_fpu_reset(), and x86_fpu_save_to().
Makes the sigcode page, the first time a process touches it.
The object keeps it, and every process maps the same page.
Definition at line 91 of file signal.c.
References kfree(), kmalloc(), M_ZERO, memcpy(), mm_page_alloc(), mm_page_dealloc(), NULL, vm_page::off, vm_page::paddr, PAGE_SIZE, pmap_page_write(), vm_page::ref, sigcode, sigcode_in(), vm_page::vm_object, and vm_object_page_insert().
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Compares a page with an offset, for the sigcode object's hashmap.
Definition at line 84 of file signal.c.
References vm_page_eq().
| void x86_return_to_user | ( | struct x86_regs * | r, |
| int | syscall ) |
Delivers the current process's pending signals on the way back to user mode: stops and default actions, a handler, and the restart (or EINTR) of a system call that a signal interrupted.
| r | the user context about to be returned to |
| syscall | whether r is returning from a system call (one that may need restarting) |
Definition at line 246 of file signal.c.
References thread::arch, x86_regs::cs, curthread, deliver(), ERESTARTNOHAND, ERESTARTSYS, thread::owner, REG_AX, REG_IP, thread::restarting, thread::sig_oldmask, thread::sig_oldmask_set, proc::sigaction, proc::sigmask, signal_take(), thread::syscall_nr, and x86_return_to_user().
Referenced by arch_syscall(), irq_dispatch(), isr_dispatch(), and x86_return_to_user().
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1.18.0