FreeTDS Development Group

[Frediano Ziglio <freddy77 AT gmail.com>]

Il giorno gio, 06/12/2007 alle 12.06 -0500, James K. Lowden ha scritto:
> Hi Freddy, 
> 
> I'm surprised by 
> 
>      $Id: dblib.c,v 1.312 2007/12/06 07:52:17 freddy77 Exp $
> 
> which replaces all  
>       dbperror(dbproc, SYBEMEM, errno); 
> with 
>       dbperror(dbproc, SYBEMEM, ENOMEM);
> 
> Was yesterday's discussion unclear?  
> 
> If malloc fails, it must set errno to ENOMEM.  
> 
> If malloc does not set errno to ENOMEM, the application should deal with
> it.  
> 
> db-lib's job in this case is only to convey what malloc(3) said.  If
> malloc returned NULL and didn't set errno to ENOMEM, that's not db-lib's
> problem.  That's for the application to settle with malloc(3).  If the
> application cannot rely on malloc to set errno, it has enough information
> from SYBEMEM.  
> 
> By hard-coding ENOMEM, you are hiding what actually happened, potentially
> lying to the application.  
> 
> Remember the application is written in C, too, and uses malloc all the
> time. It knows how to recognize malloc failures.  Win32 even has
> _set_new_mode() to control how allocation errors are handled.  I think it
> sets errno by default.  (The docs don't say so, but they do list ENOMEM as
> one of the supported errno values.)  
> 
> Would you kindly revert to 1.311?  
> 
> Thanks.  If I'm overlooking something, just say so.  
> 
> Regards, 
> 
> --jkl
> 

I compiled this program with MingW

#include <stdio.h>
#include <stdlib.h>

int main()
{
        void *p1, *p2, *p3;
        p1 = malloc(0x20000000u);
        p2 = malloc(0x20000000u);
        errno = 123;
        p3 = malloc(0x20000000u);
        printf("%p %p %p %d\n", p1, p2, p3, errno);
        return 0;
}

And it output

00540020 00000000 00000000 123

:(

MingW use the "old" msvcrt.dll (Visual C++ 2005 use a new version). As
Chistos says malloc can set errno only to ENOMEM so I think that
replacing errno with ENOMEM at the end just remove a problem with
no-compliant (and existing) malloc implementations.

Another way to fix this issue would be to have somthing like

#ifdef WIN32
   /* fix errno setting in some windows malloc implementations */
   if (msgno == SYBEMEM)
      errnum = ENOMEM;
#endif

Would you prefer this change? 

freddy77