[Tinycc-devel] Attributes for __user

[Fabrice Bellard]

I have seen that the keyword __user was added recently in the Linux 
kernel to indicate "user data" so that compile time checks can be done 
with appropriate tools.

__user is defined as (in linux/compile.h):

#ifdef __CHECKER__
  #define __user        __attribute__((noderef, address_space(1)))
  #define __kernel      /* default address space */
#else
  #define __user
  #define __kernel
#endif

It seems that gcc does not support it yet (am it right ?), but adding 
support for 'noderef' and 'address_space(N)' attributes would be easy in 
TinyCC. It would allow to do interesting checks of the Linux kernel.

The semantics could be the following:

1) Dereferencing a pointer pointing to data with the 'noderef' attribute 
causes a warning.

2) A pointer to an 'address_space(N)' data is only type-compatible with 
a pointer to the same address_space. It causes a warning if it is not.

At the same time, support for 'volatile' and 'const' typing could be added.

Any comments ?

Fabrice.