[Bug c/31949] New: SH- Aliasing problem for incompatible pointers in c code

[Bug c/31949] New: SH- Aliasing problem for incompatible pointers in c code

[Ashay dot Jaiswal at kpitcummins dot com]

Hello all,                        

I have successfully built SH4-Linux toolchain based on      
(binutils-2.17, gcc-4.2-20061205, glibc-2.5) for Renesas SH target.             

I am facing problem while executing the following C program.

 ------------------------------------------------------------------     
 #include <stdio.h>

 struct structB { int x; int y; };
 struct structC { int x; int y; };

 main()
 {
   struct structC varCs, *varCp=&varCs, **varCpp=&varCp;
   struct structB *varBp;

   varCs.x = 10;
   varCs.y = 20;
   varBp = *((struct structB **)varCpp);
   varBp->x = varBp->y;
   printf("%d",varCs.x);
 }

 ------------------------------------------------------------------             

The above program compiles successfully with the sh4-linux toolchain.           
While executing on target platform it is generating wrong result.

Observations:                

1. When the above program is compiled with '-O0' optimization the value of
   varCs.x is printed as 20, which is the expected output.
   Command: sh4-linux-gcc <file name>

2. When the above program is compiled with '-O2' optimization the program is 
   giving following errors:
   a) "Bus error" when executed on SH7780 Highlander board.
   b) "Killing process due to unaligned access in user space" when executed on 
       SH7751 R2D board.
   Command: sh4-linux-gcc -O2 <file name>

3. When the above program is compiled with '-O2' and '-fno-strict-aliasing' 
   option the value of varCs.x is printed as 20.
   Command: sh4-linux-gcc -O2 -fno-strict-aliasing <file name>

Is the above problem related to strict aliasing ? As with 'fno-strict-aliasing'
option the above code works fine.


Any help on this will be appreciated.                    

Regards,                       
Ashay Jaiswal               
KPIT Cummins Infosystems Ltd,             
Pune (INDIA)                 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
Free download of GNU based SH-Linux toolchains for Renesas' SH Series.          
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Visit http://www.kpitgnutools.com for details.                                
Latest versions of KPIT GNU SH-Linux tools were released on April 5, 2007.      
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


-- 
           Summary: SH- Aliasing problem for incompatible pointers in c code
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: Ashay dot Jaiswal at kpitcummins dot com
 GCC build triplet: i686-pc-gnu
  GCC host triplet: sh4-unknown-linux
GCC target triplet: sh4-unknown-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31949

[Bug c/31949] SH- Aliasing problem for incompatible pointers in c code

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-05-16 15:24 -------
You are accessing memory of type structC via a pointer of type structB * which
violates C aliasing rules.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31949