SHN_UNDEF symbols with non-zero value in MIPS shared object

[Uma shankar]

Hi,

Cross-MIPS gcc version (for Linux target) used  is  4.3.2

Today  I saw that .so files of MIPS contain some undef symbols with
non-zero value

The few I saw are defined in libC

Wont this confuse dynamic linker of 4.3.2  ?  ( i know that in 4.3.3.
, there is the STO_MIPS_PLT check  which  skip these. )

How does the dynamic  linker  ignore them during lookup ?
What is the purpose of these symbols ?

       thanks
          shankar

"uninitialized variable" warning from compiler

[Uma shankar]

Hi,

     I have few questions about  inbuilt mechanism of  gcc/g++  for
warning about  uninitialized variable.

I am interested in cases where  compiler is unable to warn.  I  am
aware that all the known bugs about  warning-failure are
mentioned  at  bugzilla   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639

a)  The compiler activates the warning mechanism only if  optimisation
is enabled  at compilation time with -O option. For all the bugs that
I went  through at bugzilla, the failure is not  -O level dependent.
The warning-failure occurs  for  all levels of optimisation.  So, I
believe this is the general case.

But then I came across the following  failure case.


#include 
int Check(int *a)
{
   if (*a == 0)
   {
       printf("This is sample \n");
   }
   return *a;
}
int main()
{
int call;
Check(&call);
return 0;
}
/

This one  fails  to  warn when compiled with any  level  below 3.
With -O3,  gcc  is able to warn.

Can someone tell me which is the corresponding bug logged at bugzilla ?

Are there any more such bugs which  disappear when compiled with
specific -O level ?

b)  Are there any known  "fail to do uninitialised-warning"   gcc bugs
which are language-dependent ?   I mean bugs which occur only in C++ ,
but not in C. ( Bugs which arise out of  C++ language features/syntax. ) .
If so, I would  like to know.

Elsewhere, someone pointed out to me that these are not  "bugs",  but occur
due to  tradeoff in compiler against false positive warnings.  I am
referring them
as "bugs" only because  compiler hackers do so.

                 thanks for your time
                   Uma shankar