Re: [PATCH] iommu/generic_pt: disable GCOV for iommu_amdv1.o

[Konstantin Khorenko <khorenko@virtuozzo.com>]

On 4/3/26 18:07, Jason Gunthorpe wrote:
> On Thu, Apr 02, 2026 at 05:10:12PM +0300, Konstantin Khorenko wrote:
>> With -fprofile-update=atomic in global CFLAGS_GCOV, GCC cannot
>> constant-fold FIELD_PREP() expressions inside deeply inlined page table
>> walker functions.  GCC creates .constprop clones of the inline level
>> functions, which get their own GCOV instrumentation that prevents
>> constant evaluation of compile-time checks.
> 
> That's hasn't been the issue here. gcc gets confused where it thinks a
> value is constant so the builtin_constant checks inside FIELD_PREP
> trigger, but if the value is constant then control flow leading up to
> it excludes that path ever happening.
> 
> Somehow gcov is breaking the elimination of the impossible branch, and
> I think this is all just compiler bugs.
> 
> Also, I thought this was fixed by adding the always_inline?

You are definitely right, Jason, thank you for the hint!

Sending v2 with __always_inline.

--
Konstantin Khorenko