On Tue, 22 Jul 2025 at 06:49, Kees Cook <k...@kernel.org> wrote: > > On Mon, Jul 21, 2025 at 01:14:36PM -0700, Kees Cook wrote: > > On Mon, Jul 21, 2025 at 01:47:55PM +0100, Will Deacon wrote: > > > On Sun, Jul 20, 2025 at 04:10:01PM +1000, Ard Biesheuvel wrote: > > > > On Sat, 19 Jul 2025 at 08:51, Kees Cook <k...@kernel.org> wrote: > > > > > On Fri, Jul 18, 2025 at 11:36:32AM +0300, Mike Rapoport wrote: > > > > > > On Thu, Jul 17, 2025 at 04:25:09PM -0700, Kees Cook wrote: > > > > > > > When KCOV is enabled all functions get instrumented, unless the > > > > > > > __no_sanitize_coverage attribute is used. To prepare for > > > > > > > __no_sanitize_coverage being applied to __init functions, we have > > > > > > > to > > > > > > > handle differences in how GCC's inline optimizations get > > > > > > > resolved. For > > > > > > > x86 this means forcing several functions to be inline with > > > > > > > __always_inline. > > > > > > > > > > > > > > Signed-off-by: Kees Cook <k...@kernel.org> > > > > > > > > > > > > ... > > > > > > > > > > > > > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > > > > > > > index bb19a2534224..b96746376e17 100644 > > > > > > > --- a/include/linux/memblock.h > > > > > > > +++ b/include/linux/memblock.h > > > > > > > @@ -463,7 +463,7 @@ static inline void > > > > > > > *memblock_alloc_raw(phys_addr_t size, > > > > > > > NUMA_NO_NODE); > > > > > > > } > > > > > > > > > > > > > > -static inline void *memblock_alloc_from(phys_addr_t size, > > > > > > > +static __always_inline void *memblock_alloc_from(phys_addr_t > > > > > > > size, > > > > > > > phys_addr_t align, > > > > > > > phys_addr_t min_addr) > > > > > > > > > > > > I'm curious why from all memblock_alloc* wrappers this is the only > > > > > > one that > > > > > > needs to be __always_inline? > > > > > > > > > > Thread-merge[1], adding Will Deacon, who was kind of asking the same > > > > > question. > > > > > > > > > > Based on what I can tell, GCC has kind of fragile inlining logic, in > > > > > the > > > > > sense that it can change whether or not it inlines something based on > > > > > optimizations. It looks like the kcov instrumentation being added (or > > > > > in > > > > > this case, removed) from a function changes the optimization results, > > > > > and some functions marked "inline" are _not_ inlined. In that case, > > > > > we end up > > > > > with __init code calling a function not marked __init, and we get the > > > > > build warnings I'm trying to eliminate. > > > > > > Got it, thanks for the explanation! > > > > > > > > So, to Will's comment, yes, the problem is somewhat fragile (though > > > > > using either __always_inline or __init will deterministically solve > > > > > it). > > > > > We've tripped over this before with GCC and the solution has usually > > > > > been to just use __always_inline and move on. > > > > > > > > > > > > > Given that 'inline' is already a macro in the kernel, could we just > > > > add __attribute__((__always_inline__)) to it when KCOV is enabled? > > > > > > That sounds like a more robust approach and, by the sounds of it, we > > > could predicate it on GCC too. That would also provide a neat place for > > > a comment describing the problem. > > > > > > Kees, would that work for you? > > > > That seems like an extremely large hammer for this problem, IMO. It > > feels like it could cause new strange corner cases. I'd much prefer the > > small fixes I've currently got since it keeps it focused. KCOV is > > already enabled for "allmodconfig", so any new instances would be found > > very quickly, etc. (And GCC's fragility in this regard has already been > > exposed to these cases -- it's just that I changed one of the > > combinations of __init vs inline vs instrumentation. > > > > I could give it a try, if you really prefer the big hammer approach... > > I gave it a try -- it fails spectacularly. ;) Let's stick to my small > fixes instead? >
Fair enough :-)
