Requirements for writing interrupt service functions

Interrupts are an important part of embedded systems, but they are not included in standard C. Many compiler developers have added support for interrupts to standard C, providing new keywords for marking interrupt service routines (ISRs), such as __interrupt, #program interrupt, etc. When a function is defined as an ISR, the compiler will automatically add the interrupt scene stack push and pop codes required by the interrupt service routine to the function.
　　

The interrupt service routine needs to meet the following requirements:
　　

(1) Cannot return a value;
　　

(2) Parameters cannot be passed to the ISR;
　　

(3) ISR should be as short and powerful as possible;
　　

(4) The printf(char * lpFormatString,…) function will cause reentrancy and performance issues and cannot be used in ISR.

My personal understanding 

If the interrupt service routine has a return value, to whom does it return the value?

During the operation of the system, some interrupt source must have triggered a corresponding interrupt. The interrupt service program attached to the system performs on-site processing, such as alarms and other operations, and then clears the interrupt.

In other words, the interrupt service routine is linked to a certain type of interrupt source, and the generation of these interrupt sources is random. Therefore, the interrupt service routine does not have a fixed caller or a fixed return address, so the return value is useless.