Le 03/10/2015 15:45, Joerg Sonnenberger a écrit : > On Sat, Oct 03, 2015 at 02:46:26PM +0200, Maxime Villard wrote: >> You can see that the pointer given to kmem_free() is not the one kmem_alloc >> returned. Actually, I don't understand at all what this code is supposed to >> do. Found by Brainy. > > It tries to make sure the pointer has a certain alignment. ...which > likely is something we do by default, so this is not really visible.
Regarding kmem_alloc(9) this is not necessarily true, the allocator "steals" the first few bytes of the allocation to store the requested size (see the KMEM_SIZE option in [1] which is enabled under DIAGNOSTIC). The only way I know of to guarantee alignement on a specific boundary is through uvm_km_alloc or pool_cache. [1] http://nxr.netbsd.org/xref/src/sys/kern/subr_kmem.c#63 -- Jean-Yves Migeon
