The role of [WEAK] in Keil-MDK-EEWORLD

Collect

The transplanted code is here: https://code.csdn.net/KISSMonX/freertos_f3discovery_test

In the previous article, "The meaning of the "B ." statement in ARM assembly", I also introduced the role of [WEAK]. When
I was thinking about the transplantation problem yesterday (that is, when executing the first task, I jumped directly to B . in SVC_Handler),
I thought of this problem, and then added a few macro definitions in the transplantation configuration file to solve the problem. The transplantation was successful. The details are introduced below. I
will explain it again here. See if you really understand it. :)

The first step is obviously to post the code to show off. Extract the part to be introduced in the startup file. Then write it down in the form of notes. As follows:

; Reset handler This is the key point of the startup file. But I don't see any operation to set up stack space for C program??? Calling main directly is OK? MAN???
Reset_Handler PROC
EXPORT Reset_Handler [WEAK]
IMPORT SystemInit
IMPORT __main
LDR R0, =SystemInit
BLX R0
LDR R0, =__main
BX R0
ENDP
; Dummy Exception Handlers (infinite loops which can be modified)
NMI_Handler PROC
EXPORT NMI_Handler [WEAK]
B .
ENDP
HardFault_Handler\
PROC
EXPORT HardFault_Handler [WEAK]
B .
ENDP
MemManage_Handler\
PROC
EXPORT MemManage_Handler [WEAK]
B .
ENDP
BusFault_Handler\
PROC
EXPORT BusFault_Handler [WEAK]
B .
ENDP
UsageFault_Handler\
PROC
EXPORT UsageFault_Handler [WEAK]
B .
ENDP
SVC_Handler PROC
EXPORT SVC_Handler [WEAK]
B .
ENDP
DebugMon_Handler\
PROC
EXPORT DebugMon_Handler [WEAK]
B .
ENDP
PendSV_Handler PROC
EXPORT PendSV_Handler [WEAK]
B .
ENDP
SysTick_Handler PROC
EXPORT SysTick_Handler [WEAK]
B .
ENDP
Default_Handler PROC
EXPORT WWDG_IRQHandler [WEAK]
EXPORT PVD_IRQHandler [WEAK]
EXPORT TAMPER_STAMP_IRQHandler [WEAK]
EXPORT RTC_WKUP_IRQHandler [WEAK]
EXPORT FLASH_IRQHandler [WEAK]
EXPORT RCC_IRQHandler [WEAK]
EXPORT EXTI0_IRQHandler [WEAK]
EXPORT EXTI1_IRQHandler [WEAK]
EXPORT EXTI2_TS_IRQHandler [WEAK]
EXPORT EXTI3_IRQHandler [WEAK]
EXPORT EXTI4_IRQHandler [WEAK]
EXPORT DMA1_Channel1_IRQHandler [WEAK]
EXPORT DMA1_Channel2_IRQHandler [WEAK]
EXPORT DMA1_Channel3_IRQHandler [WEAK]
EXPORT DMA1_Channel4_IRQHandler [WEAK]
EXPORT DMA1_Channel5_IRQHandler [WEAK]
EXPORT DMA1_Channel6_IRQHandler [WEAK]
EXPORT DMA1_Channel7_IRQHandler [WEAK]
EXPORT ADC1_2_IRQHandler [WEAK]
EXPORT USB_HP_CAN1_TX_IRQHandler [WEAK]
EXPORT USB_LP_CAN1_RX0_IRQHandler [WEAK]
EXPORT CAN1_RX1_IRQHandler [WEAK]
EXPORT CAN1_SCE_IRQHandler [WEAK]
EXPORT EXTI9_5_IRQHandler [WEAK]
EXPORT TIM1_BRK_TIM15_IRQHandler [WEAK]
EXPORT TIM1_UP_TIM16_IRQHandler [WEAK]
EXPORT TIM1_TRG_COM_TIM17_IRQHandler [WEAK]
EXPORT TIM1_CC_IRQHandler [WEAK]
EXPORT TIM2_IRQHandler [WEAK]
EXPORT TIM3_IRQHandler [WEAK]
EXPORT TIM4_IRQHandler [WEAK]
EXPORT I2C1_EV_IRQHandler [WEAK]
EXPORT I2C1_ER_IRQHandler [WEAK]
EXPORT I2C2_EV_IRQHandler [WEAK]
EXPORT I2C2_ER_IRQHandler [WEAK]
EXPORT SPI1_IRQHandler [WEAK]
EXPORT SPI2_IRQHandler [WEAK]
EXPORT USART1_IRQHandler [WEAK]
EXPORT USART2_IRQHandler [WEAK]
EXPORT USART3_IRQHandler [WEAK]
EXPORT EXTI15_10_IRQHandler [WEAK]
EXPORT RTC_Alarm_IRQHandler [WEAK]
EXPORT USBWakeUp_IRQHandler [WEAK]
EXPORT TIM8_BRK_IRQHandler [WEAK]
EXPORT TIM8_UP_IRQHandler [WEAK]
EXPORT TIM8_TRG_COM_IRQHandler [WEAK]
EXPORT TIM8_CC_IRQHandler [WEAK]
EXPORT ADC3_IRQHandler [WEAK]
EXPORT SPI3_IRQHandler [WEAK]
EXPORT UART4_IRQHandler [WEAK]
EXPORT UART5_IRQHandler [WEAK]
EXPORT TIM6_DAC_IRQHandler [WEAK]
EXPORT TIM7_IRQHandler [WEAK]
EXPORT DMA2_Channel1_IRQHandler [WEAK]
EXPORT DMA2_Channel2_IRQHandler [WEAK]
EXPORT DMA2_Channel3_IRQHandler [WEAK]
EXPORT DMA2_Channel4_IRQHandler [WEAK]
EXPORT DMA2_Channel5_IRQHandler [WEAK]
EXPORT ADC4_IRQHandler [WEAK]
EXPORT COMP1_2_3_IRQHandler [WEAK]
EXPORT COMP4_5_6_IRQHandler [WEAK]
EXPORT COMP7_IRQHandler [WEAK]
EXPORT USB_HP_IRQHandler [WEAK]
EXPORT USB_LP_IRQHandler [WEAK]
EXPORT USBWakeUp_RMP_IRQHandler [WEAK]
EXPORT FPU_IRQHandler [WEAK]

Then I found this sentence in the keil help document:

/* WEAK : symbol is only imported into other sources if no other source exports an alternative symbol.
If [WEAK] is used without symbol, all exported symbols are weak. */

Then there is this introduction:

This is for assembly language, don't worry if you are good at C language. If you are good at English, you can go directly to: About weak references and definitions,
which is much more detailed and accurate than what I introduced.
For those who are not good at English, forget it. The general meaning is:

// This means telling the linker:
// "I'm a little weak but I'm a gentleman. If you see the same symbol instance as mine elsewhere, just use it. Don't mind me, please ignore it!"

So... knowing this, we can solve the problem of why FreeRTOS always jumps to SVC_Handler when executing the following code.

<乱入> SVC 作用: SVCall A supervisor call (SVC) is an exception that is triggered by the SVC instruction. In an OS environment, applications can use SVC instructions to
access OS kernel functions and device drivers.

__asm void prvStartFirstTask( void )
{
PRESERVE8
/* Use the NVIC offset register to locate the stack. */
ldr r0, =0xE000ED08
ldr r0, [r0]
ldr r0, [r0]
/* Set the msp back to the start of the stack. */
msr msp, r0
/* Globally enable interrupts. */
cpsie i
etc.
isb
/* Call SVC to start the first task. */
svc 0 // System call 0, for more information about SVC, please refer to Google or the ARM Cortex-M3 Authoritative Guide
nop
}

Because the various development tool manufacturers only do simple processing for the exceptions and interrupts of these startup files. Basically, they are all infinite loops (that is, "B.").
And they are specially modified with [WEAK]. In this way, users can rewrite their own processing functions according to their needs, and as long as the names are the same, it will be OK. What if the names are different? Then, I looked for the name SVC_Handler, but didn't find it, but I found the following function
in port.c :

__asm void vPortSVCHandler( void )
{
PRESERVE8
/* Get the location of the current TCB. */
ldr r3, =pxCurrentTCB
ldr r1, [r3]
ldr r0, [r1]
/* Pop the core registers. */
ldmia r0!, {r4-r11, r14}
msr psp, r0
isb
mov r0, #0
msr basepri, r0
bx r14
}

Isn't this just SVC_Handler in disguise? Damn... Obviously I don't understand the content, so I won't explain it. I'll learn it later.
Of course, I'm not that smart. I found the files I ported before and found the following three macro definitions in portmacro.h:

#define vPortSVCHandler SVC_Handler
#define xPortSysTickHandler SysTick_Handler
#define xPortPendSVHandler PendSV_Handler

Sweep. It turns out that the macro name is also stronger than the WEAK modified one. Recompile and link correctly. Burn and program, and all tasks run normally.

Keywords：Keil-MDK WEAK Reference address：The role of [WEAK] in Keil-MDK

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