Author: Eugene Nalimov
Date: 10:36:34 10/25/05
Go up one level in this thread
On October 25, 2005 at 09:53:51, Gerd Isenberg wrote:
>On October 25, 2005 at 08:39:07, Daniel Mehrmannn wrote:
>
>>Hi,
>>
>>well i found a bug in my engine. I declare the boolean variable "stop_search" in
>>search.c. I made the error that i call this variable as "extern int stop_search"
>>from other files.
>>
>>Interesting:
>>- No compiler found this error (gcc, icc, vc 6.0 (also solaris))
>>- On Windows and Linux(!) the engine runs without any problems.
>>
>>Expect Solaris 8-10 (Sparc) family created a "segmentation fault" at first
>>access.
>>
>>How is this possible ? Why other plattforms and compiler ignored this problem ?
>>I only do a read access of this extern variable.
>>
>>see here: http://www.homer-chess.com/images/sol9.jpg
>>
>>Best,
>>Daniel
>
>Hi Daniel,
>
>it depends where the linker "allocates" the boolean variable with sizeof one
>byte. If it is "near" a 4K-Page boundary (1000h), let say at 0xffe or 0xfff, a
>byte read/write is fine, while an "external" dword read will crash.
>
>Did you do the external declaration inside a shared header file (i guess no)?
>Imagine the extern declaration is included from a shared h file,
>
>extern int foo;
>bool foo;
>
>then the compiler recognizes the error:
>error C2371: 'foo' : redefinition; different basic types
>
>while this is fine:
>
>extern bool foo;
>bool foo;
>
>Otherwise with disjoint declaration in C-files the compiler has no chance to
>detect the error, while the linker is probably overstrained with type checking
>of symbols (probably one reason that C++ names put some type information to
>symbols).
>
>Gerd
In Visual C 8.0 we will recognize such case and give you warning if the program
is compiled with link-time code generation (/GL compiler flag).
Thanks,
Eugene
t1.c:
typedef char bool;
bool c;
t2.c:
#include <stdio.h>
extern int c;
int main ()
{
printf ("%p\n", &c);
return 0;
}
D:\repro>cl /Ox /GL t1.c t2.c
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.34 for 80x86
Copyright (C) Microsoft Corporation. All rights reserved.
t1.c
t2.c
Microsoft (R) Incremental Linker Version 8.00.50727.34
Copyright (C) Microsoft Corporation. All rights reserved.
/out:t1.exe
/ltcg
t1.obj
t2.obj
warning C4742: 'c' has different alignment in 'd:\repro\t2.c' and
'd:\repro\t1.c': 4 and 1
warning C4743: 'c' has different size in 'd:\repro\t2.c' and 'd:\repro\t1.c': 4
and 1 bytes
Generating code
Finished generating code
This page took 0.01 seconds to execute
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