signed/unsigned comparison warnings in kernel header files

[Timur Tabi <timur.tabi@xxxxxxxxxxx>]

I have a driver that needs to be compilable with as many different 
kernel versions as possible.  One problem I'm having is that if I 
specify "-Wall" to catch all warnings, the compiler sometimes complains 
about the kernel header files, not my code.  For example, with SuSE 8.2:

/usr/src/linux-2.4.20.SuSE/include/asm/pgalloc.h: In function 
'get_pgd_slow':
/usr/src/linux-2.4.20.SuSE/include/asm/pgalloc.h:38: warning: comparison 
between signed and unsigned
/usr/src/linux-2.4.20.SuSE/include/asm/pgalloc.h: In function 
`free_pgd_slow':
/usr/src/linux-2.4.20.SuSE/include/asm/pgalloc.h:99: warning: comparison 
between signed and unsigned

Technically, these warnings are correct.  A signed integer variable is 
being compared with unsigned constants.  So I have two questions:

1) Why do warnings like this show up only on some kernel versions, and 
not others?  We've compiled our code with several Red Hat and SuSE 
versions, and this is the only one that has this problem.

2) Are certain warning levels just not acceptable for compiling the 
kernel?  In other words, is "-Wall" always a bad idea?  If so, what 
warning level should I use?

--
Timur Tabi
Staff Software Engineer
timur.tabi@xxxxxxxxxxx

--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/