[Bug c/86092] New: global constant pointer optimization

[srinivas.sundar at vvdntech dot in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86092

Bug ID: 86092
   Summary: global constant pointer optimization
   Product: gcc
   Version: 5.3.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: srinivas.sundar at vvdntech dot in
  Target Milestone: ---

Here is my sample kernel code. which works fine in gcc-4, had an issue with
gcc-5. I get both the print even if I allocate the dynamic memory to
kern_buff_p.
Disassemble of code gives the constant variable is optimized in the If
statement. Can you provide me any FLAG to disable this optimization with this
constant pointers.


static char*  const kern_buff_p;

static int __init hello_start(void)
{

 if(!kern_buff_p)
printk(KERN_INFO "buffer is NULL for first time \n");

  *((char**)(unsigned long
int)((&kern_buff_p)))=kmalloc(KERN_BUF_SIZE,GFP_KERNEL);

 if(!kern_buff_p)
printk(KERN_INFO "buffer is NULL for second time \n");
}

[Bug c/86092] global constant pointer optimization

[srinivas.sundar at vvdntech dot in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86092

--- Comment #2 from Srinivas Achary  ---
Sorry that I am new to this.
Is there any possibility to make this code work, without changing the variable
attribute. GCC-4 has no issue with this code. What special flags have been
included in the GCC-5.

During disassemble the 
if(!kern_buff_p)
--
is changed to 
if x0 is kern_buff_p
mov x0, #0

This should be 
mov x0,[x0]

[Bug c/86092] global constant pointer optimization

[srinivas.sundar at vvdntech dot in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86092

Srinivas Achary  changed:

   What|Removed |Added

 Status|RESOLVED|UNCONFIRMED
 Resolution|INVALID |---

--- Comment #3 from Srinivas Achary  ---
I have tried disabling all ipa FLAGS

[Bug c/86092] global constant pointer optimization

[srinivas.sundar at vvdntech dot in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86092

--- Comment #5 from Srinivas Achary  ---
thank you Marc.
What I have shown here is just an example sample code. But I have code which
makes use of kern_buff_p variable in many place.If I use volatile that might
reduce my code speed.

Any how the kern_buff_p initial value is NULL
and the variable have been allocated the memory during runtime without any
issue.

The problem is during compilation, the compiler optimizes all my conditional
statements used with this constant pointers. Due to this, I am not able to run
my code in New machines.

[Bug c/88126] New: Need Compiler warning

[srinivas.sundar at vvdntech dot in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88126

Bug ID: 88126
   Summary: Need Compiler warning
   Product: gcc
   Version: 5.3.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: srinivas.sundar at vvdntech dot in
  Target Milestone: ---

int main()
{
   unsigned long ul=4294967296;
   unsigned int var;

   var=ul;  // how to get warning

}

The value of "var" will be different in 64bit system and 32bit system. Is it
possible to get compilation warning in 64bit system.