On Thu, 3 Oct 2002, Igor Pechtchanski wrote:
> On Thu, 3 Oct 2002, Allen Leung wrote:
>
> > Dear List,
> >
> > In a system I'm writing I need to catch page faults and find out
> > the fault address and the fault type (read or write). On most unices
> > I can get this information inside a sigaction handler.
> > E.g. on Linux, something like this works:
> >
> > ==========================================================
> > void fault_handler(int sig, siginfo_t * info, void * uap)
> > {
> > vm_addr_t addr;
> > VM::access_t access;
> >
> > /* fault address */
> > addr = (vm_addr_t)info->si_addr;
> > /* 1 for write; 0 for read */
> > access = (VM::access_t)
> > ((((ucontext_t *)uap)->uc_mcontext.gregs[13] & 0x2) != 0);
> > ...
> > }
> > ==========================================================
> >
> > However, cygwin's signal handling mechanism doesn't propagate these
> > information to the signal handler. On mingw, I can use window's API
> > to get the info I need:
> >
> > ==========================================================
> > LONG WINAPI fault_handler(LPEXCEPTION_POINTERS info)
> > {
> > vm_addr_t addr;
> > VM::access_t access;
> >
> > if (info->ExceptionRecord->ExceptionCode != EXCEPTION_ACCESS_VIOLATION)
> > return EXCEPTION_CONTINUE_SEARCH;
> >
> > access = (VM::access_t)info->ExceptionRecord->ExceptionInformation[0];
> > addr = (vm_addr_t)info->ExceptionRecord->ExceptionInformation[1];
> >
> > ...
> > }
> >
> > SetUnhandledExceptionFilter(fault_handler);
> > ==========================================================
> >
> > However, this doesn't work on cygwin because apparently cygwin is
> > overriding my own fault handler. So I'm wondering: how can I bypass
> > cygwin's signal handling mechanism so that I get hold of the page fault
> > information?
> >
> > Thanks,
> > Allen
>
> Hey, Allen! (Of all places to meet here :-D)
>
> Cygwin currently does not support SA_SIGINFO signal handling. It's on the
> TODO list ( http://cygwin.com//cgi-bin/cygwin-todo.cgi?20020722.130725 ),
> but I didn't have the time to work on it yet...
>
> As far as I know, there is currently no way to retrieve the fault
> information from a Unix-style signal handler in Cygwin. You might try to
> patch the Cygwin DLL to ignore a particular signal (in
> winsup/cygwin/exceptions.cc), and then write your own Windows-style
> handler... It'll probably be quite a bit of work. Another idea would be
> to include a callback to your own function in handle_exceptions(). In
> either case, you'll have to build a custom cygwin1.dll...
> Igor
Allen,
Actually, the first thing to try should probably be
#include <exceptions.h>
#include <sys/cygwin.h>
...
exception_list el;
cygwin_internal(CW_INIT_EXCEPTIONS, &el);
el.handler = your_handler;
...
I'm not sure how to clean this up afterwards, but theoretically this
should work... Chris Faylor will hopefully correct me if I'm wrong.
Igor
--
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"Water molecules expand as they grow warmer" (C) Popular Science, Oct'02, p.51
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