157 lines
5.2 KiB
C++
157 lines
5.2 KiB
C++
/* exception.h
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Copyright 1996, 1997, 1998, 2000, 2001, 2005, 2010, 2011, 1012, 2013
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Red Hat, Inc.
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This software is a copyrighted work licensed under the terms of the
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Cygwin license. Please consult the file "CYGWIN_LICENSE" for
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details. */
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#pragma once
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#ifndef __x86_64__
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/* Documentation on the innards of 32 bit Windows exception handling (i.e.
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from the perspective of a compiler implementor) apparently doesn't exist.
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However, the following came from Onno Hovers <onno@stack.urc.tue.nl>
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The first pointer to the chain of handlers is in the thread environment block
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at FS:[0]. This chain has the following format:
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typedef struct __EXCEPTION_FRAME
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{
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struct __EXCEPTION_FRAME *Prev; /-* pointer to the previous frame *-/
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PEXCEPTION_HANDLER Handler; /-* handler function *-/
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}
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You register an exception handler in your compiler with this simple ASM
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sequence:
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PUSH _MyExceptionHandler
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PUSH FS:[0]
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MOV FS:[0],ESP
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An exception frame MUST be on the stack! The frame may have more fields and
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both Visual C++ and Borland C++ use more fields for themselves.
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When an exception occurs the system calls all handlers starting with the
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handler at FS:0, and then the previous etc. until one handler returns
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ExceptionContinueExecution, which is 0. If a handler does not want to handle
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the exception it should just return ExceptionContinueSearch, which is 1.
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The handler has the following parameters:
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ehandler (
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PEXCEPTION_RECORD erecord,
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PEXCEPTION_FRAME myframe,
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PCONTEXT context, /-* context before and after *-/
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PVOID dispatch) /-* something *-/
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When a handler wants to handle the exception, it has some alternatives:
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-one is to do do something about the exception condition, like emulating
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an invalid instruction, mapping memory where there was a page fault, etc.
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If the handler wants to have the context of the thread that causes the
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exception changed, it should make that change in the context passed to the
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handler.
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-the second alternative is to call all exception handlers again, indicating
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that you want them to clean up. This way all the __finally blocks get
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executed. After doing that you change the context passed to the handler so
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the code starts executing in the except block. For this purpose you could
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call RtlUnwind. This (undocumented) function calls all exception handlers
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up to but not including the exception frame passed to it. If NULL is passed
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as exception frame RtlUnwind calls all exception handlers and then exits the
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process. The parameters to RtlUnwind are:
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RtlUnwind (
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PEXCEPTION_FRAME endframe,
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PVOID unusedEip,
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PEXCEPTION_RECORD erecord,
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DWORD returnEax)
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You should set unusedEip to the address where RtlUnwind should return like
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this:
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PUSH 0
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PUSH OFFSET ReturnUnwind
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PUSH 0
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PUSH 0
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CALL RtlUnwind
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ReturnUnwind:
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.....
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If no EXCEPTION_RECORD is passed, RtlUnwind makes a default exception
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record. In any case, the ExceptionFlags part of this record has the
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EH_UNWINDING (=2), flag set. (and EH_EXIT_UNWIND (=4), when NULL is passed as the end
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frame.).
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The handler for a exception as well as a for unwinds may be executed in the
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thread causing the exception, but may also be executed in another (special
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exception) thread. So it is not wise to make any assumptions about that!
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As an alternative you may consider the SetUnhandledExceptionFilter API
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to install your own exception filter. This one is documented.
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*/
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/* The January 1994 MSJ has an article entitled "Clearer, More Comprehensive
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Error Processing with Win32 Structured Exception Handling". It goes into
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a teensy bit of detail of the innards of exception handling (i.e. what we
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have to do). */
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typedef int (exception_handler) (EXCEPTION_RECORD *, struct _exception_list *,
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CONTEXT *, void *);
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typedef struct _exception_list
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{
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struct _exception_list *prev;
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exception_handler *handler;
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} exception_list;
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extern exception_list *_except_list asm ("%fs:0");
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#endif /* !__x86_64 */
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class exception
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{
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#ifdef __x86_64__
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static bool handler_installed;
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static int handle (LPEXCEPTION_POINTERS);
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#else
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exception_list el;
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exception_list *save;
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static int handle (EXCEPTION_RECORD *, exception_list *, CONTEXT *, void *);
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#endif /* __x86_64__ */
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public:
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exception () __attribute__ ((always_inline))
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{
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#ifdef __x86_64__
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if (!handler_installed)
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{
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handler_installed = true;
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/* The unhandled exception filter goes first. It won't work if the
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executable is debugged, but then the vectored continue handler
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kicks in. For some reason the vectored continue handler doesn't
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get called if no unhandled exception filter is installed. */
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SetUnhandledExceptionFilter (handle);
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AddVectoredContinueHandler (1, handle);
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}
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#else
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save = _except_list;
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el.handler = handle;
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el.prev = _except_list;
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_except_list = ⪙
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#endif /* __x86_64__ */
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};
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#ifndef __x86_64__
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~exception () __attribute__ ((always_inline)) { _except_list = save; }
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#endif /* !__x86_64__ */
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};
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class cygwin_exception
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{
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PUINT_PTR framep;
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PCONTEXT ctx;
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EXCEPTION_RECORD *e;
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void dump_exception ();
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public:
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cygwin_exception (PUINT_PTR in_framep, PCONTEXT in_ctx = NULL, EXCEPTION_RECORD *in_e = NULL):
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framep (in_framep), ctx (in_ctx), e (in_e) {}
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void dumpstack ();
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PCONTEXT context () const {return ctx;}
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};
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