aarch64架构有多个异常方式，例如：中断，软件异常，同步异常等等
这些异常在代码中需要对应一个内存地址用作跳转，在aarch64中，每个异常都可以设置入口函数，从而实现异常的处理。与armv7不同的是，v8上默认向量表的空间更大了，支持0x80大小
在linux中，异常向量表通过如下定义
SYM_CODE_START(vectors) kernel_ventry 1, t, 64, sync // Synchronous EL1t kernel_ventry 1, t, 64, irq // IRQ EL1t kernel_ventry 1, t, 64, fiq // FIQ EL1t kernel_ventry 1, t, 64, error // Error EL1t kernel_ventry 1, h, 64, sync // Synchronous EL1h kernel_ventry 1, h, 64, irq // IRQ EL1h kernel_ventry 1, h, 64, fiq // FIQ EL1h kernel_ventry 1, h, 64, error // Error EL1h kernel_ventry 0, t, 64, sync // Synchronous 64-bit EL0 kernel_ventry 0, t, 64, irq // IRQ 64-bit EL0 kernel_ventry 0, t, 64, fiq // FIQ 64-bit EL0 kernel_ventry 0, t, 64, error // Error 64-bit EL0 kernel_ventry 0, t, 32, sync // Synchronous 32-bit EL0 kernel_ventry 0, t, 32, irq // IRQ 32-bit EL0 kernel_ventry 0, t, 32, fiq // FIQ 32-bit EL0 kernel_ventry 0, t, 32, error // Error 32-bit EL0 SYM_CODE_END(vectors)
通过上面可以看到，linux定义了这些异常的实现，右边有注释，就不解释了。
代码如下：
.macro kernel_ventry, el:req, ht:req, regsize:req, label:req .align 7 .Lventry_start\@: .if \el == 0 /* * This must be the first instruction of the EL0 vector entries. It is * skipped by the trampoline vectors, to trigger the cleanup. */ b .Lskip_tramp_vectors_cleanup\@ .if \regsize == 64 mrs x30, tpidrro_el0 msr tpidrro_el0, xzr .else mov x30, xzr .endif .Lskip_tramp_vectors_cleanup\@: .endif sub sp, sp, #PT_REGS_SIZE #ifdef CONFIG_VMAP_STACK /* * Test whether the SP has overflowed, without corrupting a GPR. * Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT) * should always be zero. */ add sp, sp, x0 // sp' = sp + x0 sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp tbnz x0, #THREAD_SHIFT, 0f sub x0, sp, x0 // x0'' = sp' - x0' = (sp + x0) - sp = x0 sub sp, sp, x0 // sp'' = sp' - x0 = (sp + x0) - x0 = sp b el\el\ht\()_\regsize\()_\label 0: /* * Either we've just detected an overflow, or we've taken an exception * while on the overflow stack. Either way, we won't return to * userspace, and can clobber EL0 registers to free up GPRs. */ /* Stash the original SP (minus PT_REGS_SIZE) in tpidr_el0. */ msr tpidr_el0, x0 /* Recover the original x0 value and stash it in tpidrro_el0 */ sub x0, sp, x0 msr tpidrro_el0, x0 /* Switch to the overflow stack */ adr_this_cpu sp, overflow_stack + OVERFLOW_STACK_SIZE, x0 /* * Check whether we were already on the overflow stack. This may happen * after panic() re-enables interrupts. */ mrs x0, tpidr_el0 // sp of interrupted context sub x0, sp, x0 // delta with top of overflow stack tst x0, #~(OVERFLOW_STACK_SIZE - 1) // within range? b.ne __bad_stack // no? -> bad stack pointer /* We were already on the overflow stack. Restore sp/x0 and carry on. */ sub sp, sp, x0 mrs x0, tpidrro_el0 #endif b el\el\ht\()_\regsize\()_\label .org .Lventry_start\@ + 128 // Did we overflow the ventry slot? .endm .macro tramp_alias, dst, sym, tmp mov_q \dst, TRAMP_VALIAS adr_l \tmp, \sym add \dst, \dst, \tmp adr_l \tmp, .entry.tramp.text sub \dst, \dst, \tmp .endm
这段汇编有点长，我跳过一下清理和栈必要操作，下面开始解析关键部分。
首先查看宏定义如下
.macro kernel_ventry, el:req, ht:req, regsize:req, label:req
这里宏有四个参数，其中req指的是required，四个参数含义如下：
b el\el\ht\()_\regsize\()_\label
这里对应c是如下
el##${el}${ht}_${regsize}_${label}
以fiq举例如下：
kernel_ventry 1, t, 64, fi
则跳转函数el1t_64_fiq
.org .Lventry_start\@ + 128
这里确保每个异常向量入口占用恰好 128 字节的空间。
为了确定汇编宏扩展是否正确，可以通过nm查看，如下
# nm entry.o | awk '{print $3}' | grep "^el" el0t_32_error el0t_32_fiq el0t_32_irq el0t_32_sync el0t_64_error el0t_64_fiq el0t_64_irq el0t_64_sync el1h_64_error el1h_64_fiq el1h_64_irq el1h_64_sync el1t_64_error el1t_64_fiq el1t_64_irq el1t_64_sync