On Sun, Mar 3, 2024 at 9:10 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Sun, Mar 03 2024 at 20:03, Uros Bizjak wrote: > > On Sun, Mar 3, 2024 at 5:31 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >> I did not follow the __set_gs work closely, so I don't know whether Uros > >> ever tried to actually mark the per CPU variable __set_gs right away, > >> which would obviously catch the above 'foo' nonsense. > > > > No, because [1]: > > > > "gcc does not provide a way to remove segment qualifiers, which is needed > > to use typeof() to create local instances of the per-cpu variable. For > > this reason, do not use the segment qualifier for per-cpu variables, and > > do casting using the segment qualifier instead." > > Right. I just figured that out myself when playing with it in user > space. > > That's so sad because it would provide us compiler based __percpu > validation. Unfortunately, the c compiler can't strip qualifiers, so typeof() is of limited use also when const and volatile qualifiers are used. Perhaps some extension could be introduced to c standard to provide an unqualified type, e.g. typeof_unqual(). Uros. > Right now this simply does not work and __verify_pcp_ptr(ptr) is not > doing anything except when sparse looks at it. > > Sigh. > > tglx >
