On Fri, Jul 18, 2025 at 03:51:28PM -0700, Kees Cook wrote: > On Fri, Jul 18, 2025 at 11:36:32AM +0300, Mike Rapoport wrote: > > Hi Kees, > > > > 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 <kees@xxxxxxxxxx> > > > > ... > > > > > 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. > > 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. > > For memblock_alloc*, it appears to be that the heuristic GCC uses > resulted in only memblock_alloc_from() being a problem in this case. I > can certainly mark them all as __always_inline if that is preferred. We had a few of those already converted to __always_inline, so I'm ok with continuing to fix them one at at time. Gives a feeling of job security ;-) > -- > Kees Cook -- Sincerely yours, Mike.
