From: Jason Gunthorpe <jgg@ziepe.ca>
To: Konstantin Khorenko <khorenko@virtuozzo.com>
Cc: "Joerg Roedel" <joro@8bytes.org>, "Will Deacon" <will@kernel.org>,
"Robin Murphy" <robin.murphy@arm.com>,
"Kevin Tian" <kevin.tian@intel.com>,
"Peter Oberparleiter" <oberpar@linux.ibm.com>,
"Mikhail Zaslonko" <zaslonko@linux.ibm.com>,
iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
"Pavel Tikhomirov" <ptikhomirov@virtuozzo.com>,
"Vasileios Almpanis" <vasileios.almpanis@virtuozzo.com>,
"Thomas Weißschuh" <linux@weissschuh.net>
Subject: Re: [PATCH] iommu/generic_pt: disable GCOV for iommu_amdv1.o
Date: Fri, 3 Apr 2026 13:07:29 -0300 [thread overview]
Message-ID: <20260403160729.GC2551565@ziepe.ca> (raw)
In-Reply-To: <20260402141012.1437095-2-khorenko@virtuozzo.com>
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?
Jason
next prev parent reply other threads:[~2026-04-03 16:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-02 14:10 [PATCH 0/1] iommu/generic_pt: disable GCOV for iommu_amdv1.o Konstantin Khorenko
2026-04-02 14:10 ` [PATCH] " Konstantin Khorenko
2026-04-03 16:07 ` Jason Gunthorpe [this message]
2026-04-09 17:01 ` Konstantin Khorenko
2026-04-09 17:01 ` [PATCH v2 0/1] iommu/generic_pt: fix GCOV build failure for amdv1 Konstantin Khorenko
2026-04-09 17:01 ` [PATCH v2] iommu/generic_pt: use __always_inline for amdv1pt_install_leaf_entry() Konstantin Khorenko
2026-04-09 18:29 ` Jason Gunthorpe
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