How to unwind the signal handler using the longjmp on Windows environment.

main.c

#include <stdio.h>
#include <signal.h>
#include <setjmp.h>

jmp_buf jb;

// Run in windows, this handler called from SEH filter context from "_seh_filter_exe()".
// The SEH __try - __except() block contains at "__scrt_common_main_seh(),"
// the callgraph is:
//   __scrt_common_main_seh() --> __try --> main() --> [SEGV] --> __except() --> _seh_filter_exe() --> handler()
// But the "__except(...)" expression has correct only EBP register except ESP register (!!)
// Therefore the "_seh_filter_exe()" called before NO any unroll stacks,
// the "handler()" function at deeper stack than "main(),"
// We can use the longjmp() and unwinding without any stack corruption.
// (CAUTION: These descriptions doesn't contain breaking context for async race calls.)

// Just before called main (__scrt_common_main_seh() __try block)
// EAX = 0012A57C EBX = 006EE000 ECX = 005E0000 EDX = 0012A57C ESI = 0012132A EDI = 0012132A
// EIP = 00121D72 ESP = 005DFE38 EBP = 005DFE8C EFL = 00000246 

// Just enter __except() expression code
// EAX = 00000000 EBX = 00000000 ECX = 00121DC3 EDX = 00000000 ESI = 00000000 EDI = 00000000
// EIP = 00121DC3 ESP = 005DF708 EBP = 005DFE8C EFL = 00000246   (ESP deeper but EBP adjusted at __try block)

void handler(int sig) {
    longjmp(jb, 1);
}

int main()
{
    signal(SIGSEGV, handler);

    // This variable will corrupt if the handler() calls after stack unrolls by SEH __except() handling.
    volatile int v = 123;

    if (setjmp(jb) == 0)
    {
        char*p = nullptr;
        char a = *p;
    }

    printf("%d\n", v);
}