head.s分析(7)：init_early_exception_vectors

 

快乐虾

http://blog.youkuaiyun.com/lights_joy/

lights@hb165.com

 

本文适用于

ADI bf561 DSP

uclinux-2008r1.5-rc3 (移植到vdsp5)

Visual DSP++ 5.0(update 5)

 

欢迎转载，但请保留作者信息

 

#ifdef CONFIG_EARLY_PRINTK

     SP += -12;

     call.x _init_early_exception_vectors;

     SP += 12;

#endif

所调用的这个函数将设置EVT2-EVT15的中断向量。同时将所有的返回地址也指向同一个位置。

/*

 * Set up a temporary Event Vector Table, so if something bad happens before

 * the kernel is fully started, it doesn't vector off into somewhere we don't

 * know

 */

 

asmlinkage void __init init_early_exception_vectors(void)

{

     SSYNC();

 

     /* cannot program in software:

      * evt0 - emulation (jtag)

      * evt1 - reset

      */

     bfin_write_EVT2(early_trap);

     bfin_write_EVT3(early_trap);

     bfin_write_EVT5(early_trap);

     bfin_write_EVT6(early_trap);

     bfin_write_EVT7(early_trap);

     bfin_write_EVT8(early_trap);

     bfin_write_EVT9(early_trap);

     bfin_write_EVT10(early_trap);

     bfin_write_EVT11(early_trap);

     bfin_write_EVT12(early_trap);

     bfin_write_EVT13(early_trap);

     bfin_write_EVT14(early_trap);

     bfin_write_EVT15(early_trap);

     CSYNC();

 

     /* Set all the return from interrupt, exception, NMI to a known place

      * so if we do a RETI, RETX or RETN by mistake - we go somewhere known

      * Note - don't change RETS - we are in a subroutine, or

      * RETE - since it might screw up if emulator is attached

      */

     asm("/tRETI = %0; RETX = %0; RETN = %0;/n"

         : : "p"(early_trap));

 

}

其中RETI为中断服务的返回地址，RETX为异常中断的返回地址，RETN为不可屏蔽中断的返回地址。

early_trap这一中断入口的定义在linux-2.6.x/arch/blackfin/mach-common/entry.S中：

ENTRY(_early_trap)

     SAVE_ALL_SYS

     trace_buffer_stop(p0,r0)

 

     /* Turn caches off, to ensure we don't get double exceptions */

 

     P4.L = LO(IMEM_CONTROL);

     P4.H = HI(IMEM_CONTROL);

 

     R5 = [P4];              /* Control Register*/

     BITCLR(R5,ENICPLB_P);

     CLI R1;

     SSYNC;          /* SSYNC required before writing to IMEM_CONTROL. */

     .align 8;

     [P4] = R5;

     SSYNC;

 

     P4.L = LO(DMEM_CONTROL);

     P4.H = HI(DMEM_CONTROL);

     R5 = [P4];

     BITCLR(R5,ENDCPLB_P);

     SSYNC;          /* SSYNC required before writing to DMEM_CONTROL. */

     .align 8;

     [P4] = R5;

     SSYNC;

     STI R1;

 

     r0 = sp;        /* stack frame pt_regs pointer argument ==> r0 */

     r1 = RETX;

 

     SP += -12;

     call.x _early_trap_c;

     SP += 12;

ENDPROC(_early_trap)

这段代码功能比较简单，将寄存器入栈，关闭cache，然后调用c的函数early_trap_c，由于early_trap_c直接就panic，一旦进入这个中断入口就不会再退出，所有在这个中断服务中没有返回的指令。这里比较有意思的是调用early_trap_c时的参数传递。

early_trap_c的函数原型为：

asmlinkage void __init early_trap_c(struct pt_regs *fp, void *retaddr)

它将接受一个结构体的指针和一个返回地址作为参数。在参数传递过程中，对于少于三个参数的函数调用，使用R0来传递第一个参数，使用R1来传递第二个参数。因此在上述汇编代码中，有

     r0 = sp;        /* stack frame pt_regs pointer argument ==> r0 */

     r1 = RETX;

那么结构体的内容来自于哪里呢？先看看pt_regs的定义：

/* this struct defines the way the registers are stored on the

   stack during a system call. */

 

struct pt_regs {

     long orig_pc;

     long ipend;

     long seqstat;

     long rete;

     long retn;

     long retx;

     long pc;      /* PC == RETI */

     long rets;

     long reserved;          /* Used as scratch during system calls */

     long astat;

     long lb1;

     long lb0;

     long lt1;

     long lt0;

     long lc1;

     long lc0;

     long a1w;

     long a1x;

     long a0w;

     long a0x;

     long b3;

     long b2;

     long b1;

     long b0;

     long l3;

     long l2;

     long l1;

     long l0;

     long m3;

     long m2;

     long m1;

     long m0;

     long i3;

     long i2;

     long i1;

     long i0;

     long usp;

     long fp;

     long p5;

     long p4;

     long p3;

     long p2;

     long p1;

     long p0;

     long r7;

     long r6;

     long r5;

     long r4;

     long r3;

     long r2;

     long r1;

     long r0;

     long orig_r0;

     long orig_p0;

     long syscfg;

};

再看看SAVE_ALL_SYS的定义：

#define SAVE_ALL_SYS        save_context_no_interrupts

#define save_context_no_interrupts                      /

     [--sp] = SYSCFG;                     /

     [--sp] = P0;  /* orig_p0 */                    /

     [--sp] = R0;  /* orig_r0 */                    /

     [--sp] = ( R7:0, P5:0 );                       /

     [--sp] = fp;                     /

     [--sp] = usp;                    /

                       /

     [--sp] = i0;                     /

     [--sp] = i1;                     /

     [--sp] = i2;                     /

     [--sp] = i3;                     /

                       /

     [--sp] = m0;                     /

     [--sp] = m1;                     /

     [--sp] = m2;                     /

     [--sp] = m3;                     /

                       /

     [--sp] = l0;                     /

     [--sp] = l1;                     /

     [--sp] = l2;                     /

     [--sp] = l3;                     /

                       /

     [--sp] = b0;                     /

     [--sp] = b1;                     /

     [--sp] = b2;                     /

     [--sp] = b3;                     /

     [--sp] = a0.x;                       /

     [--sp] = a0.w;                       /

     [--sp] = a1.x;                       /

     [--sp] = a1.w;                       /

                       /

     [--sp] = LC0;                    /

     [--sp] = LC1;                    /

     [--sp] = LT0;                    /

     [--sp] = LT1;                    /

     [--sp] = LB0;                    /

     [--sp] = LB1;                    /

                       /

     [--sp] = ASTAT;                      /

                       /

     [--sp] = r0;  /* Skip reserved */                       /

     [--sp] = RETS;                       /

     r0 = RETI;                       /

     [--sp] = r0;                     /

     [--sp] = RETX;                       /

     [--sp] = RETN;                       /

     [--sp] = RETE;                       /

     [--sp] = SEQSTAT;                    /

     [--sp] = r0;  /* Skip IPEND as well. */                      /

     [--sp] = r0;  /*orig_pc*/                      /

     /* Clear all L registers.  */                      /

     r0 = 0 (x);                      /

     l0 = r0;                    /

     l1 = r0;                    /

     l2 = r0;                    /

     l3 = r0;                    /

//.endm

入栈顺序刚好和pt_regs结构体的成员次序相反，由于入栈操作时SP指针是向下增长的，而结构体成员的排列则是向上增长的，因此入栈操作即相当于对结构体的成员一一赋值。

最后看看early_trap_c的实现：

asmlinkage void __init early_trap_c(struct pt_regs *fp, void *retaddr)

{

     /* This can happen before the uart is initialized, so initialize

      * the UART now

      */

     if (likely(early_console == NULL))

         setup_early_printk(DEFAULT_EARLY_PORT);

 

     dump_bfin_mem(fp);

     show_regs(fp);

     dump_bfin_trace_buffer();

 

     panic("Died early");

}

输出寄存器的内容，然后panic！

 

1       参考资料

head.s分析(1)：保存u-boot传递过来的指针(2009-1-19)

head.s分析(2)：SYSCFG配置(2009-1-19)

head.s分析(3)：数据及指针寄存器清0(2009-1-19)

head.s分析(4)：关闭CACHE(2009-01-19)

head.s分析(5)：关闭串口(2009-01-19)

head.s分析(6)：栈指针初始化(2009-01-19)