On Wed, Jan 22, 2025 at 02:37:30PM +0100, Peter Zijlstra wrote: > On Tue, Jan 21, 2025 at 06:31:20PM -0800, Josh Poimboeuf wrote: > > +/* > > + * The context cookie is a unique identifier which allows post-processing > > to > > + * correlate kernel trace(s) with user unwinds. The high 12 bits are the > > CPU > > s/12/16/ ? > > > + * id; the lower 48 bits are a per-CPU entry counter. > > + */ > > +static u64 ctx_to_cookie(u64 cpu, u64 ctx) > > +{ > > + BUILD_BUG_ON(NR_CPUS > 65535); > > + return (ctx & ((1UL << 48) - 1)) | (cpu << 48); > > +}
Also, I have to note that 0 is a valid return value here, which will give a ton of fun.