ARM 汇编向量表定义 - 为什么向量以这种方式定义？

Question

我正在检查 STM32F1 的启动汇编代码，有些事情让我很困惑 这是代码

.syntax unified
.arch armv7-m 
.thumb 

/* Initial vector table */
        .section "vectors" 
    .long    _STACK_TOP             /* Top of Stack */
    .long    _reset_Handler        /* Reset Handler */
    .long    _NMI_Handler           /* NMI Handler */
    .long    _HardFault_Handler     /* Hard Fault Handler */
    .long    _MemManage_Handler    /* Reserved */
    .long    _BusFault_Handler     /* Reserved */
    .long    _UsageFault_Handler   /* Reserved */
    .long    0                     /* Reserved */
    .long    0                     /* Reserved */
    .long    0                     /* Reserved */
    .long    0                     /* Reserved */
    .long    _SVCall_Handler       /* SVCall Handler */
    .long    _DebugMonitor_Handler /* Reserved */
    .long    0                     /* Reserved */
    .long    _PendSV_Handler        /* PendSV Handler */
    .long    _SysTick_Handler       /* SysTick Handler */

# Some memory setup code

.macro                 def_rewritable_handler   handler 
    .thumb_func
    .weak    \handler
    .type    \handler, %function
    \handler:   b  . @@ Branch forever in default state
.endm

def_rewritable_handler  _NMI_Handler             /* NMI HANDLER */
def_rewritable_handler  _HardFault_Handler       /* HARD FAULT Handler */
def_rewritable_handler  _MemManage_Handler    /* Reserved */
def_rewritable_handler  _BusFault_Handler     /* Reserved */
def_rewritable_handler  _UsageFault_Handler   /* Reserved */ 
def_rewritable_handler  _SVCall_Handler             /* SVCALL Handler */
def_rewritable_handler  _PendSV_Handler          /* PENDSV Handler */
def_rewritable_handler  _SysTick_Handler         /* SYSTICK Handler */ 
def_rewritable_handler  _DebugMonitor_Handler /* Reserved */ 
def_rewritable_handler  _WWDG_IRQHandler            /* WWDG_IRQHandler */
def_rewritable_handler  _PVD_IRQHandler             /* PVD_IRQHandler */
def_rewritable_handler  _TAMPER_IRQHandler          /* TAMPER_IRQHandler */
def_rewritable_handler  _RTC_IRQHandler             /* RTC_IRQHandler */
def_rewritable_handler  _FLASH_IRQHandler           /* FLASH_IRQHandler */
def_rewritable_handler  _RCC_IRQHandler             /* RCC_IRQHandler */
def_rewritable_handler  _EXTI0_IRQHandler           /* EXTI0_IRQHandler */
def_rewritable_handler  _EXTI1_IRQHandler           /* EXTI1_IRQHandler */
def_rewritable_handler  _EXTI2_IRQHandler           /* EXTI2_IRQHandler */
def_rewritable_handler  _EXTI3_IRQHandler           /* EXTI3_IRQHandler */
def_rewritable_handler  _EXTI4_IRQHandler           /* EXTI4_IRQHandler */
def_rewritable_handler  _DMA1_Channel1_IRQHandler   /* DMA1_Channel1_IRQHandler */
def_rewritable_handler  _DMA1_Channel2_IRQHandler   /* DMA1_Channel2_IRQHandler */
def_rewritable_handler  _DMA1_Channel3_IRQHandler   /* DMA1_Channel3_IRQHandler */
def_rewritable_handler  _DMA1_Channel4_IRQHandler   /* DMA1_Channel4_IRQHandler */
def_rewritable_handler  _DMA1_Channel5_IRQHandler   /* DMA1_Channel5_IRQHandler */
def_rewritable_handler  _DMA1_Channel6_IRQHandler   /* DMA1_Channel6_IRQHandler */
def_rewritable_handler  _DMA1_Channel7_IRQHandler   /* DMA1_Channel7_IRQHandler */
def_rewritable_handler  _ADC1_2_IRQHandler          /* ADC1_2_IRQHandler */
def_rewritable_handler  _USB_HP_CAN1_TX_IRQHandler  /* USB_HP_CAN1_TX_IRQHandler */
def_rewritable_handler  _USB_LP_CAN1_RX0_IRQHandler /* USB_LP_CAN1_RX0_IRQHandler */
def_rewritable_handler  _CAN1_RX1_IRQHandler        /* CAN1_RX1_IRQHandler */
def_rewritable_handler  _CAN1_SCE_IRQHandler        /* CAN1_SCE_IRQHandler */
def_rewritable_handler  _EXTI9_5_IRQHandler         /* EXTI9_5_IRQHandler */
def_rewritable_handler  _TIM1_BRK_IRQHandler        /* TIM1_BRK_IRQHandler */
def_rewritable_handler  _TIM1_UP_IRQHandler         /* TIM1_UP_IRQHandler */
def_rewritable_handler  _TIM1_TRG_COM_IRQHandler    /* TIM1_TRG_COM_IRQHandler */
def_rewritable_handler  _TIM1_CC_IRQHandler         /* TIM1_CC_IRQHandler */
def_rewritable_handler  _TIM2_IRQHandler            /* TIM2_IRQHandler */
def_rewritable_handler  _TIM3_IRQHandler            /* TIM3_IRQHandler */
def_rewritable_handler  _I2C1_EV_IRQHandler         /* I2C1_EV_IRQHandler */
def_rewritable_handler  _I2C1_ER_IRQHandler         /* I2C1_ER_IRQHandler */
def_rewritable_handler  _SPI1_IRQHandler            /* SPI1_IRQHandler */
def_rewritable_handler  _USART1_IRQHandler          /* USART1_IRQHandler */
def_rewritable_handler  _USART2_IRQHandler          /* USART2_IRQHandler */
def_rewritable_handler  _EXTI15_10_IRQHandler       /* EXTI15_10_IRQHandler */
def_rewritable_handler  _RTCAlarm_IRQHandler        /* RTCAlarm_IRQHandler */
def_rewritable_handler  _USBWakeUp_IRQHandler       /* USBWakeUp_IRQHandler */

        .end 

据我所知，.long 分配 4 个字节的内存，通常在它之前使用标签来标记其内存位置。但是 .long 之后有一个标签，其中一些标签可以在这个文件中找到，有些不是 我试图用谷歌搜索这种语法但一无所获，请给我一些解释

Answer 1

.long symbol_name 发出 4 个字节，其中 value = 该符号的绝对地址。 （正如@Erik 在 cmets 中解释的那样。）

这就像您写 bl symbol 时一样 - 它是对该符号的引用，而不是定义。

例如在 C 中，int foo = bar; 仅定义 foo，而不是 bar。

---

label 是name: 是一行中的第一件事，并定义了一个符号（地址 = 标签的位置）。

.long name 不是标签，只是对符号的引用（应该由其他地方的标签定义，或者只是在链接描述文件中设置。）

x: .long y 会在包含值y 的单词的起始地址放置标签x。