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Re: [HACKERS] Win32 WEXITSTATUS too

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Takayuki Tsunakawa <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>
Cc: PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
Subject: Re: [HACKERS] Win32 WEXITSTATUS too
Date: 2007-01-23 03:35:11
Message-ID: 200701230335.l0N3ZBT29151@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Takayuki Tsunakawa wrote:
> From: "Bruce Momjian" <bruce(at)momjian(dot)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.

--
  Bruce Momjian   bruce(at)momjian(dot)us
  EnterpriseDB    http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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