I have run into problem using sigaddset() with constant signal argument 
in kernel code.

A code like the following gets miscompiled:

sigset_t a;
sigset_t b;
sigset_t c;

...........
sigaddset(&a, const1);
sigaddset(&a,  const2);
................................
b =a;    /* this line causes incorrect code; any 64-bit assignment seems 
to cause a problem! */
sigaddset(&c, const2);
sigaddset(&c,  const3);
/* more sigaddset to c */

All versions of compilers and all kernel versions are affected. The 
problem is also reproducible in user space (with kernel sigaddset 
definition). Looking at the dissassembly (or running in the debugger) 
clearly shows that gcc miscompiled the code.

Attached please find a C code (can be compiled into module or 
executable) that demonstrates the problem. Attached is also a patch that 
fixes the problem (the patch was prepared against 2.6 tree).

I defined sigaddset a macro (similar to sigismember) that calls one 
function for constant argument and another for variable. In addition to 
fixing the problem, it also makes sigaddset() faster for constant arguments.

To be on the safe side, I changed sigdelset() in the same way (I think 
the same gcc bug may apply).


-- 
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Constantine Gavrilov
Kernel Developer
Qlusters Software Ltd
1 Azrieli Center, Tel-Aviv
Phone: +972-3-6081977
Fax:   +972-3-6081841
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