win32: register SEH in startup code (i386 only)

Needed to handle signal() etc. with msvcrt

win32/lib/chkstk.S

@@ -75,3 +75,125 @@ t1:
 /* ---------------------------------------------- */
 #endif
 /* ---------------------------------------------- */
+
+
+/* ---------------------------------------------- */
+#ifndef TCC_TARGET_X86_64
+/* ---------------------------------------------- */
+
+/*
+    int _except_handler3(
+       PEXCEPTION_RECORD exception_record,
+       PEXCEPTION_REGISTRATION registration,
+       PCONTEXT context,
+       PEXCEPTION_REGISTRATION dispatcher
+    );
+
+    int __cdecl _XcptFilter(
+       unsigned long xcptnum,
+       PEXCEPTION_POINTERS pxcptinfoptrs
+    );
+
+    struct _sehrec {
+       void *esp;                // 0
+       void *exception_pointers; // 1
+       void *prev;               // 2
+       void *handler;            // 3
+       void *scopetable;         // 4
+       int trylevel;             // 5
+       void *ebp                 // 6
+    };
+
+    // this is what the assembler code below means:
+    __try
+    {
+         // ...
+    }
+    __except (_XcptFilter(GetExceptionCode(), GetExceptionInformation()))
+    {
+         exit(GetExceptionCode());
+    }
+*/
+
+.globl _exception_info
+_exception_info:
+    mov 1*4-24(%ebp),%eax
+    ret
+
+.globl _exception_code
+_exception_code:
+    call _exception_info
+    mov (%eax),%eax
+    mov (%eax),%eax
+    ret
+
+seh_filter:
+    call _exception_info
+    push %eax
+    call _exception_code
+    push %eax
+    call _XcptFilter
+    add $ 8,%esp
+    ret
+
+seh_except:
+    mov 0*4-24(%ebp),%esp
+    call _exception_code
+    push %eax
+    call _exit
+
+// msvcrt wants scopetables aligned and in read-only segment (using .text)
+.align 4
+seh_scopetable:
+    .long -1
+    .long seh_filter
+    .long seh_except
+
+seh_handler:
+    jmp _except_handler3
+
+.globl __try__
+__try__:
+    push %ebp
+    mov 8(%esp),%ebp
+
+//    void *esp;
+    lea 12(%esp),%eax
+    mov %eax,0*4(%ebp)
+
+//    void *exception_pointers;
+    xor %eax,%eax
+    mov %eax,1*4(%ebp)
+
+//    void *prev;
+    mov %fs:0,%eax
+    mov %eax,2*4(%ebp)
+
+//    void *handler;
+    mov $ seh_handler,%eax
+    mov %eax,3*4(%ebp)
+
+//    void *scopetable;
+    mov $ seh_scopetable,%eax
+    mov %eax,4*4(%ebp)
+
+//    int trylevel;
+    xor %eax,%eax
+    mov %eax,5*4(%ebp)
+
+//    register new SEH
+    lea 2*4(%ebp),%eax
+    mov %eax,%fs:0
+
+    pop %ebp
+    ret
+
+/* ---------------------------------------------- */
+#else
+/* ---------------------------------------------- */
+
+/* SEH on x86-64 not implemented */
+
+/* ---------------------------------------------- */
+#endif
+/* ---------------------------------------------- */