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Date: Wed, 16 Oct 2024 08:39:25 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: David Marchand <david.marchand@redhat.com>
Cc: Mattias =?UTF-8?B?UsO2bm5ibG9t?= <mattias.ronnblom@ericsson.com>,
dev@dpdk.org, Mattias =?UTF-8?B?UsO2bm5ibG9t?= <hofors@lysator.liu.se>
Subject: Re: [PATCH 2/2] devtools: forbid the use of ffs compiler builtins
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On Wed, 16 Oct 2024 17:32:27 +0200
David Marchand <david.marchand@redhat.com> wrote:
> On Wed, Oct 16, 2024 at 5:04=E2=80=AFPM Stephen Hemminger
> <stephen@networkplumber.org> wrote:
> >
> > On Wed, 16 Oct 2024 15:54:11 +0200
> > Mattias R=C3=B6nnblom <mattias.ronnblom@ericsson.com> wrote:
> > =20
> > > Extend checkpatches.sh to detect the use of __builtin_(ffs|ffsll).
> > >
> > > These intrinsics are not available in MSVC, and there are perfectly
> > > serviceable alternatives in <rte_bitops.h>.
> > >
> > > Signed-off-by: Mattias R=C3=B6nnblom <mattias.ronnblom@ericsson.com>
> > > Suggested-by: David Marchand <david.marchand@redhat.com> =20
> >
> > Shouldn't this apply to all _builtin_ functions.
> >
> > There are a lot of drivers still doing this. =20
>=20
> - The updated check here is about use of __builtin_XXX instead of DPDK
> bit count ops.
> So when you refer to all builtin functions, there may be other
> builtins related to bit count we are missing, but at least the current
> patch is better than before.
>=20
>=20
> - On the larger topic of refusing *any* __builtin_, some use of them
> are "legit" under compiler checks.
> So the check would have to skip headers where wrappers are provided to
> the rest of DPDK.
> This seems possible, but a larger and probably more tricky change for now.
>=20
> Are you ok if we go with this patch as is, in a first step?
>=20
>=20
Examples of direct use of builtin
app/dumpcap/main.c: log2 =3D sizeof(size) * 8 - __builtin_clzl(size - =
1);
app/test-dma-perf/benchmark.c: __builtin_ia32_clflush(dat=
a + offset);
drivers/bus/fslmc/qbman/include/compat.h:#define likely(x) __builtin_=
expect(!!(x), 1)
drivers/bus/fslmc/qbman/include/compat.h:#define unlikely(x) __builtin_=
expect(!!(x), 0)
drivers/common/nfp/nfp_platform.h:#define __bf_shf(x) (__builtin_ffsll(x) =
- 1)
drivers/crypto/ccp/ccp_dev.c: first_zero =3D __builtin_ffsl(~word);
app/test/test_memcpy_perf.c: if (__builtin_constant_p(n)) =20
drivers/net/bonding/rte_eth_bond_pmd.c: if (__builtin_popcountl(li=
nk_speeds) !=3D 2) {
Think that direct use of __builitin_expect should be flagged.
And the lots of __builtin_in mlx5 should also be flagged.
=09
=20