Re: [go-nuts] Re: Issue with Adding Exception Vector Handler in Go

Sat, 18 Jan 2025 05:32:19 -0800

Go and C handle errors differently: 
  • Go: Go uses error values returned from functions to handle errors. This approach makes error handling explicit and encourages developers to handle them gracefully. 
  • C: C often uses exceptions and signals to handle errors. However, C's error handling mechanisms don't directly translate to Go's error handling approach. 
Handling Errors in CGO: 
  • Return Values: Many C functions return error codes or status values. You can check these values in your Go code and handle them accordingly. 
  • errno: C often sets the global variable errno to indicate an error. You can access errno in Go using syscall.Errno. 
  • C++ Exceptions: C++ exceptions are not directly supported by CGO. If your C++ code throws exceptions, you can wrap the code in a C function that catches the exceptions and returns an error code. 
Example: 

package main

/*
#include <stdio.h>
#include <stdlib.h>

int divide(int a, int b, int *result) {
    if (b == 0) {
        return -1; // Error: division by zero
    }
    *result = a / b;
    return 0; // Success
}
*/
import "C"
import (
	"fmt"
	"syscall"
)

func main() {
	var result C.int
	ret := C.divide(10, 0, &result)
	if ret != 0 {
		if ret == -1 {
			fmt.Println("Error: division by zero")
		} else {
			fmt.Println("Error:", syscall.Errno(-ret))
		}
	} else {
		fmt.Println("Result:", int(result))
	}
}

Important Considerations: 
  • Error Handling Consistency: Strive to maintain consistent error handling across your Go and C code. 
  • Panic: Avoid panicking in CGO code. Instead, return error values to your Go code to handle them gracefully. 
  • Memory Management: Be mindful of memory allocation and deallocation when working with CGO. 
Alternatives to CGO: 
  • Go Wrappers: If possible, consider writing pure Go wrappers around C libraries to provide a more idiomatic Go interface. 
  • RPC: For more complex interactions, consider using RPC mechanisms like gRPC to communicate between Go and C components. 

Generative AI is experimental.

On Jan 18, 2025, at 7:21 AM, rudeus greyrat <rudeusquagmir...@gmail.com> wrote:


The issue seems to come from firstcontinuehandler, I tweaked it a little and it is getting better

```
// It seems Windows searches ContinueHandler's list even
// if ExceptionHandler returns EXCEPTION_CONTINUE_EXECUTION.
// firstcontinuehandler will stop that search,
// if exceptionhandler did the same earlier.
//
// It is nosplit for the same reason as exceptionhandler.
//
//go:nosplit
func firstcontinuehandler(info *exceptionrecord, r *context, gp *g) int32 {
    print("Went in first Continue Handler")
if !isgoexception(info, r) {
        println("It is not go exception")
return _EXCEPTION_CONTINUE_SEARCH
}
    println("It is a go exception")
return _EXCEPTION_CONTINUE_EXECUTION
}
```

Seems go is not allowing "non Go exception" to be handled by Go code
Le samedi 18 janvier 2025 à 12:51:12 UTC+1, rudeus greyrat a écrit :
Any idea please ? Been stuck at this for quite some time, seems that Go is neglecting the return uintptr(handler.EXCEPTION_CONTINUE_SEARCH) and going into panic mode ...


Le vendredi 17 janvier 2025 à 16:30:24 UTC+1, rudeus greyrat a écrit :

asked the question here too if people want to have syntax highlight

Le vendredi 17 janvier 2025 à 14:16:30 UTC+1, rudeus greyrat a écrit :
PS: I know there is defer recover mechanism in Go that can be used to handle exception... But I would like to use AddVectoredExceptionHandler (maybe it is already used behind the scene with defer recover ?) because I can inspect the thread context in myhandler function

Le vendredi 17 janvier 2025 à 13:17:07 UTC+1, rudeus greyrat a écrit :
I want to be able to catch windows exception and do stuff with it (mainly for hardware break point later).

I created a custom function to add a Vectored Exception Handler using the windows API call AddVectoredExceptionHandler:
```
func AddVEH(myHandler PVECTORED_EXCEPTION_HANDLER) error {
    kernel32 := syscall.NewLazyDLL("kernel32.dll")
addVectoredExceptionHandler := kernel32.NewProc("AddVectoredExceptionHandler")

   
_, _, err := addVectoredExceptionHandler.Call(
uintptr(1),
syscall.NewCallback(func(exceptionInfo *EXCEPTION_POINTERS) uintptr {
return myHandler(exceptionInfo)
}),
)
    if err != nil {
        fmt.Println("Error Setting the VEH")
        fmt.Println(err.Error())
    }
    return err
}
```

I test it with a custom exception I raise:
```
func myHandler(exceptionInfo *handler.EXCEPTION_POINTERS) uintptr {
println("Exception occurred! ---> Code")
println(exceptionInfo.ExceptionRecord.ExceptionCode)
println("It happends in life, lets continue")
return ^uintptr(0) // EXCEPTION_CONTINUE_EXECUTION = -1
}

func main() {
handler.AddVEH(myHandler)

raiseCustomException() // Just Raises a custom EXCEPTION with RaiseException winapi and code 0xE0000001

println("Continued")
}
```

As I return with EXCEPTION_CONTINUE_EXECUTION, I expect that `println("Continued")` will be executed. However, it is not the case at all:
```
Error Setting the VEH
    The operation completed successfully.
Exception occurred! ---> Code
3758096385
It happends in life, lets continue
Exception 0xe0000001 0x7eb71d5fb17c 0x1b 0x7ffc54e4b699
PC=0x7ffc54e4b699

runtime.cgocall(0xf1dde0, 0xc000049b30)
        runtime/cgocall.go:167 +0x3e fp=0xc00006fe28 sp=0xc00006fdc0 pc=0xf10a7e
syscall.SyscallN(0xc00001e410?, {0xc0000121c0?, 0x0?, 0xf39a00?})
```

As you see the program enter the handler function but never continues, rather it exit and print the stack trace... 

Not sure if it is because of syscall.NewCallback or something else ...





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