switch_mm中是进行页表的切换,即将下一个的pgd的开始物理地址放入CP15中的C2寄存器。进程的pgd的虚拟地址存放在task_struct结构中的pgd指针中,通过__virt_to_phys 宏可以转变成 成物理地址。
static inline void
switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk, unsigned int cpu)
{
if (prev != next)
cpu_switch_mm(next->pgd, tsk);
}
#define cpu_switch_mm(pgd,tsk) cpu_set_pgd(__virt_to_phys((unsigned long)(pgd)))
#define cpu_get_pgd() \
({ \
unsigned long pg; \
__asm__("mrc p15, 0, %0, c2, c0, 0" \
: "=r" (pg)); \
pg &= ~0x3fff; \
(pgd_t *)phys_to_virt(pg); \
})
switch_to()完成进程上下文的切换,通过调用汇编函数__switch_to完成,其实现比较简单,也就是保存prev进程的上下文信息,该上下文信息由context_save_struct结构描述,包括主要的寄存器,然后将next的上下文信息读出,信息保存在task_struct中的thread.save中TSS_SAVE标识了thread.save在task_struct中的位置。
/*
* Register switch for ARMv3 and ARMv4 processors
* r0 = previous, r1 = next, return previous.
* previous and next are guaranteed not to be the same.
*/
ENTRY(__switch_to)
stmfd sp!, {r4 - sl, fp, lr} @ Store most regs on stack
mrs ip, cpsr
str ip, [sp, #-4]! @ Save cpsr_SVC
str sp, [r0, #TSS_SAVE] @ Save sp_SVC
ldr sp, [r1, #TSS_SAVE] @ Get saved sp_SVC
ldr r2, [r1, #TSS_DOMAIN]
ldr ip, [sp], #4
mcr p15, 0, r2, c3, c0 @ Set domain register
msr spsr, ip @ Save tasks CPSR into SPSR for this return
ldmfd sp!, {r4 - sl, fp, pc}^ @ Load all regs saved previously
struct context_save_struct {
unsigned long cpsr;
unsigned long r4;
unsigned long r5;
unsigned long r6;
unsigned long r7;
unsigned long r8;
unsigned long r9;
unsigned long sl;
unsigned long fp;
unsigned long pc;
};
[C语言系列]C# 和 Linux 时间戳转换 [Web开发]PHP flock文件锁介绍 [Web开发]flock() Linux下的文件锁 [电脑应用]Linux下的六个免费的虚拟主机管理系统介绍 [电脑应用]Linux数据库大比拚 [操作系统]在Windows中玩转Linux操作系统 [办公软件]在RedHat Linux 9里安装gaim0.80 [办公软件]掌握 Linux 调试技术 [办公软件]理解 Linux 配置文件 [聊天工具]Real10 & Xpdf installation on Linux Box
|