ARMv8 ELx VBAR

VBAR_EL1, Vector Base Address Register (EL1)

Holds the vector base address for any exception that is taken to EL1.

 

 

VBAR_EL2, Vector Base Address Register (EL2)

Holds the vector base address for any exception that is taken to EL2.

 

 

VBAR_EL3, Vector Base Address Register (EL3) 

Holds the vector base address for any exception that is taken to EL3.

ARMv8 针对异常进入定义的基址寄存器。即存放异常向量表的基地址，一般在系统启动的早期进行设置。

Disassembly of section .text:

00000000f8000000 :
    f8000000:    aa0003f4     mov    x20, x0
    f8000004:    aa0103f5     mov    x21, x1
    f8000008:    aa0203f6     mov    x22, x2
    f800000c:    aa0303f7     mov    x23, x3
    f8000010:    10043f80     adr    x0, f8008800 获取异常向量基地址
    f8000014:    d51ec000     msr    vbar_el3, x0 设置基地址到EL3,此时处于EL3级别
    f8000018:    d5033fdf     isb
    f800001c:    58000421     ldr    x1, f80000a0 把后面地址f80000a0存放到X1
    f8000020:    f9400020     ldr    x0, [x1]， 这里把X1里面存放的内容作为地址，获取此地址里面内容
    f8000024:    92400c00     and    x0, x0, #0xf ; 检查低4位是否有内容，
    f8000028:    f100001f     cmp    x0, #0x0； 比较是否为非0指
    f800002c:    5403e361     b.ne    f8007c98  // b.any 非0则跳转到bl2_sysdump处理
    f8000030:    94000022     bl    f80000b8 //处理跳转到EL1
    f8000034:    10047e60     adr    x0, f8009000 ;继续把el1的异常向量基地址设置
    f8000038:    d518c000     msr    vbar_el1, x0 到vbar_el1中
    f800003c:    d5033fdf     isb 再进行指令同步
    f8000040:    d50344ff     msr    daifclr, #0x4 把 SError interrupt给掩码了。
    f8000044:    d2820141     mov    x1, #0x100a                    // #4106
    f8000048:    d5381000     mrs    x0, sctlr_el1
    f800004c:    aa010000     orr    x0, x0, x1，这里执行逻辑或指令，就是把上面立即数4106即(0B1 0000 0000 1010)
    f8000050:    d5181000     msr    sctlr_el1, x0; 这里是配置SCTLR_EL1寄存器
    f8000054:    d5033fdf     isb 再次执行指令同步
    f8000058:    10067d40     adr    x0, f800d000 <__RODATA_END__>获取地址，即存放数据的数据段基地址
    f800005c:    100b7d21     adr    x1, f8017000 <__BL2_END__> 存放数据的结束地址
    f8000060:    cb000021     sub    x1, x1, x0 ；获取这个数据段长度
    f8000064:    94001f70     bl    f8007e24 ，这个是调用dcache 无效，即
    f8000068:    58000200     ldr    x0, f80000a8 装载地址，即把f80000a8 放入X0
    f800006c:    58000221     ldr    x1, f80000b0 把f80000b0 放入x1
    f8000070:    94001f7c     bl    f8007e60 此函数针对x0和x1之间的存储空间进行清零处理
    f8000074:    94001f01     bl    f8007c78 设置栈
    f8000078:    aa1403e0     mov    x0, x20 恢复x20 - x23 到 x0-x3
    f800007c:    aa1503e1     mov    x1, x21
    f8000080:    aa1603e2     mov    x2, x22
    f8000084:    aa1703e3     mov    x3, x23
    f8000088:    94001bbc     bl    f8006f78 跳转到此处运行平台相关处理
    f800008c:    94000860     bl    f800220c 体希结构相关初始化
    f8000090:    940019f4     bl    f8006860 调用bl2的main处理函数
    f8000094:    94001fc8     bl    f8007fb4
    f8000098:    d503201f     nop
    f800009c:    00000000     .inst    0x00000000 ; undefined
    f80000a0:    fa722180     .word    0xfa722180
    f80000a4:    00000000     .word    0x00000000
    f80000a8:    f800e200     .word    0xf800e200 起始地址
    f80000ac:    00000000     .word    0x00000000
    f80000b0:    00003e50     .word    0x00003e50 长度
    f80000b4:    00000000     .word    0x00000000

 

即数4106即(0B1 0000 0000 1010)

SCTLR_EL1, System Control Register (EL1)

Provides top level control of the system, including its memory system, at EL1 and EL0.

I, bit [12]
       Instruction access Cacheability control, for accesses at EL0 and EL1:
       0b0 All instruction access to Normal memory from EL0 and EL1 are Non-cacheable for all levels of instruction and unified cache.If the value of SCTLR_EL1.M is 0, instruction accesses from stage 1 of the EL1&0 translation regime are to Normal, Outer Shareable, Inner Non-cacheable, Outer Non-cacheable memory.
       0b1 This control has no effect on the Cacheability of instruction access to Normal memory from EL0 and EL1.If the value of SCTLR_EL1.M is 0, instruction accesses from stage 1 of the EL1&0 translation regime are to Normal, Outer Shareable, Inner Write-Through, Outer Write-Through memory.

也就是说，上面操作开启了I cache，即指令cache开启。

 

SA, bit [3] 栈指针对齐检查
SP Alignment check enable. When set to 1, if a load or store instruction executed at EL1 uses the
SP as the base address and the SP is not aligned to a 16-byte boundary, then a SP alignment fault
exception is generated. For more information, see SP alignment checking on page D1-2164.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit
has no effect on the PE.
In a system where the PE resets into EL1, this field resets to an architecturally UNKNOWN value.

C, bit [2] 数据cache关闭
Cacheability control, for data accesses.
0b0 All data access to Normal memory from EL0 and EL1, and all Normal memory accesses
to the EL1&0 stage 1 translation tables, are Non-cacheable for all levels of data and
unified cache.
0b1 This control has no effect on the Cacheability of:
• Data access to Normal memory from EL0 and EL1.
• Normal memory accesses to the EL1&0 stage 1 translation tables.

A, bit [1]
Alignment check enable. This is the enable bit for Alignment fault checking at EL1 and EL0.
0b0 Alignment fault checking disabled when executing at EL1 or EL0.
Instructions that load or store one or more registers, other than load/store exclusive and
load-acquire/store-release, do not check that the address being accessed is aligned to the
size of the data element(s) being accessed.
0b1 Alignment fault checking enabled when executing at EL1 or EL0.
All instructions that load or store one or more registers have an alignment check that the
address being accessed is aligned to the size of the data element(s) being accessed. If
this check fails it causes an Alignment fault, which is taken as a Data Abort exception.

 

M, bit [0] MMU关闭
MMU enable for EL1 and EL0 stage 1 address translation. Possible values of this bit are:
0b0 EL1 and EL0 stage 1 address translation disabled.
See the SCTLR_EL1.I field for the behavior of instruction accesses to Normal memory.
0b1 EL1 and EL0 stage 1 address translation enabled.