Re: sign extension for 32bit syscalls on ppc64

On Mon, 1 May 2006 10:05:18 +1000 Stephen Rothwell [off-list ref] wrote:

Try mkdirat. openat has a compat wrapper that has the dfd paramater
declared as a unsigned int and passes it to sys_openat, whose first
paramter is decalred to be int, so the sign extension gets done.

OK, I actually tried this and it works! :-(

I traced the code path and it turns out that the place we check for the
-100 (in do_path_lookup), the compiler has used a cmpwi instruction and so
ignores the top 32 bits.  Thus we get away with the ABI abuse!

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/