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? Will
