Re: [HACKERS] Win32 WEXITSTATUS too - Mailing list pgsql-patches

On Mon, Jan 22, 2007 at 10:35:11PM -0500, Bruce Momjian wrote:
> Takayuki Tsunakawa wrote:
> > From: "Bruce Momjian" <bruce@momjian.us>
> > > OK, I have tested on MinGW and found I can use FormatMessage() to
> > print
> > > a description for all ERROR* system() failures, rather than print a
> > hex
> > > value.  This removes the need for a URL or lookup of hex values.
> > > Attached and applied.
> >
> > Excuse me if I'm misunderstanding, but I'm afraid you are mixing up
> > Win32 error codes and exception codes.  I saw the following fragment
> > in your patch:
> >
> > !  * On MinGW, system() returns STATUS_* values.  MSVC might be
> > !  * different.  To test, create a binary that does *(NULL), and
> > !  * then create a second binary that calls it via system(),
> > !  * and check the return value of system().  On MinGW, it is
> > !  * 0xC0000005 == STATUS_ACCESS_VIOLATION, and 0x5 is a value
> > !  * FormatMessage() can look up.  GetLastError() does not work;
> > !  * always zero.
> >
> > Exception codes and error codes are different and not related.  In the
> > above test, 0xC0000005 is an "exception code". On the other hand, what
> > FormatMessage() accepts is an error code.  Error codes can't derived
> > from exception codes.  Stripping off 0xC bit from an exception code
> > does not convert it to an error code.
> > I suspect the reason why you misunderstood is that the descriptions
> > are similar:
> > the description for exception 0xC0000005 (STATUS_ACCESS_VIOLATION) is
> > "access violation" (though the text can't be obtained).  This is
> > caused by an illegal memory access.  This is a program bug.
> > The description for 0x5 (ERROR_ACCESS_DENIED) is "Access is denied."
> > This is caused by permission checks.  This is not a bug, and can
> > happen normally.
> >
> > Try "1.0 / 0.0" (devide by zero) instead of (*NULL).  What would your
> > patch display?  The exception would be 0xC000008E
> > (STATUS_FLOAT_DIVIDE_BY_ZERO), I think.  0x8E is ERROR_BUSY_DRIVE.
>
> Yes, you are 100% correct that I had exceptions and errors confused.  I
> have backed out the patch that used FormatMessage(), and instead of
> using a URL, the message is now:
>
>     child process was terminated by exception %X
>     See /include/ntstatus.h for a description of the hex value.
>
> When I search for /include/ntstatus.h, I get the Wine page first, so
> hopefully we can mark this item as completed.

Are you entirely sure that ntstatus.h is where to look? Because per
whatever docs I've found, that contains "device driver errors" and *not*
exception codes.
If it really is, then using FormatMessage is correct - because it's not
an exception value, it'sa  DDK error value. AFAIK, that's not the same
as an exception. (Though you have to add the search of ntdll.dll, of
course)

//Magnus