From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 86FAE397B05 for ; Wed, 17 Jun 2026 05:38:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=150.107.74.76 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781674714; cv=none; b=ZKmm/7MGNYf3+GacxYOV5giK5zoG0kJX/4iQBH2dbMn/EYJ+sMBw9nbWSpJ+RuUCcqHcdCqmVoDNtC7JeBhIohsZBs5ZVMpGpUpJOavx9whDJSiqq8RNGgCHhByF3AqBdoPoU8tt28DWRlFmSlDeCN22D+KrPVbeuSIFsPxIczw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781674714; c=relaxed/simple; bh=GJZRhBe9+ZbR7IgqjExTiYC0lGNI5xkMB5nn0iIhdVI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UdMJ6Xw2Lfq5bfdaxmqKJH5ERHSL7hG1bshC7BGYZ6jeynZI07RL5bxJhasEHuL36W6yL0b695dGD2DGctGOA4wFC9J8pZOuRgMvsvfrpOzgoUWfA+/HEiqU5qRDx+a38LxGnDNK/5GNzNNmW7MKtwDBe0mYqj2PTQz3XWclEFw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au; spf=pass smtp.mailfrom=gandalf.ozlabs.org; dkim=pass (2048-bit key) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.b=cnm95y3z; arc=none smtp.client-ip=150.107.74.76 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gandalf.ozlabs.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.b="cnm95y3z" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202606; t=1781674705; bh=38urtEuWv26TMUF1V0+n28fv0nlyJxpaN4Pye7n0NbQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cnm95y3zzrSmbVXo+X0zxiYdrpXa7EPI6xIw8ccO15uHr6PSefsbfWsO51Nkw3L8R oWRDkvaFpuh0YKI/Si+uUy5l8DE2xrIcRqM4QXDKJvflzGfiYif+e+azZzQHBl/tG3 dkYOZL6rvF81z+aROt3AjleApxJRGZ16IaLaucWR2tANEWR9PfS+jarFgtLypB9pNj GK51BlOpHmTOOqVJcivnYAvAaC344DRyiGbyw5dJl6dkN/GpQpn8+f4K3fu7KBkjAM NEMnX9PcS26IB8uW7uVQaBSse6tqIM99gJmuZQVpDTJkfVnLv4I0wd93MQDIjbv/63 6/dnWCCD3PlnQ== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4ggCM536s4z58pc; Wed, 17 Jun 2026 15:38:25 +1000 (AEST) Date: Wed, 17 Jun 2026 15:37:29 +1000 From: David Gibson To: Tom Rini Cc: devicetree-compiler@vger.kernel.org Subject: Re: [PATCH] libfdt: fdt_check_full: Add can_assume(PERFECT) check Message-ID: References: <20260526203022.4006434-1-trini@konsulko.com> <20260527043859.GC1858239@bill-the-cat> Precedence: bulk X-Mailing-List: devicetree-compiler@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="p2+YznaeSOZSzEzW" Content-Disposition: inline In-Reply-To: <20260527043859.GC1858239@bill-the-cat> --p2+YznaeSOZSzEzW Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, May 26, 2026 at 10:38:59PM -0600, Tom Rini wrote: > On Wed, May 27, 2026 at 02:23:20PM +1000, David Gibson wrote: > > On Tue, May 26, 2026 at 02:30:22PM -0600, Tom Rini wrote: > > > In this function from fdt_check.c we have (reasonably and as the name > > > implies) a number of checks on the DTB. However, there are cases where > > > we may wish to assume that we have been given a perfect DTB already a= nd > > > do nothing here. Add a test for can_assume(PERFECT) as the first check > > > in this function and if true, perform no checks. > > >=20 > > > Signed-off-by: Tom Rini > > > --- > > > Along the lines of the patches I posted back in December, in U-Boot S= PL > > > we just don't have the space for this check much of the time and so h= ave > > > always omitted it (going back to at least when Simon posted the initi= al > > > patch to make libfdt/fdt_check.c here). This is another case where it= 's > > > a noticeable size win for us. I had missed this change in particular > > > because we had in turn missed catching up on fdt_check_full being mov= ed > > > out of fdt_ro.c and in to fdt_check.c. > >=20 > > I'm not necessarily against this, but I have some misgivings. > >=20 > > fdt_check_full() is (deliberately) not called from anywhere else in > > libfdt - it's intended to allow the user to explicitly do a full > > validity check on the tree. Given that meaning, I'm not sure it's > > wise to turn it into a no-op based on the assume flags. > >=20 > > Your comment seems to imply that the issue here is size - simply > > having this function compiled - rather than being too expensive when > > (explicitly) called. That's a little surprising to me - it's in its > > own compilation unit, specifically so that the linker can omit it if > > it's not used. Is there something unusual about your build > > environment that's not letting that happen? >=20 > So, we have code like this: > /* Get the total space reserved for FDT in blob */ > live_fdt =3D bloblist_get_blob(BLOBLISTT_CONTROL_FDT, &blob_size); > if (live_fdt !=3D gd->fdt_blob) > return -ENOENT; >=20 > ret =3D fdt_check_full(live_fdt, blob_size); > if (ret) > return fdtdec_ret_to_errno(ret); >=20 > And this is compiled on TPL, SPL and full U-Boot builds. On the first > two, we're just too space constrained to do this check. So it's not the > linker doing the right thing or not, it's avoiding having to #if the > code directly (or rather, CONFIG_VAL(...)). My line of thinking was that > since ASSUME_PERFECT is that everything is really perfect, this is the > way to go. Yes, it's a little odd to have both "call the validation > function" and "the validation function does not validate" but that's > just because in the second case, we explicitly configured ourself to not > validate anything. Ok, convincing enough. Merged. > And FWIW, that's really how we use the assume mask in U-Boot, either > 0xff or 0x0. It's a case where we're either passing along the tree we > bundled with ourself (and so we can assume it's fine) or it's passed > along (and we verify). --=20 David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson --p2+YznaeSOZSzEzW Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmoyMpAACgkQzQJF27ox 2Gc1cw//db15Us61tkj3PGojsp6haqEJDMqV52CxEojQ6t1i97HaPOWaT44zfluR qC/Iu4T0fK4oMz2Qdy0Y3FgYNg5vwQj1O8mMiNBbVLSkYcHJVQquKXwN9I24Izx8 8oSIZ1dLUr405lmxcB6sFwFW9XhjP2eFnN3d3zTieUEaCkiVvE4SkdldRPi06lAq 0Va6gmvOMQn5wbUtUMdxrWHxvzxIkuqd4KG//0pxGJsrb4tOpNwuEza+EMOzWTCS 0/d0k4pcGxu3uxDguceXjZonNZQAKoi3d10M6SedTKWDhVkINMee58J2gDqO57VX f3eObYzHkhkdWbV20m0U28R4PH4soMPG5C6I/Ux9vlv8U1cC3gXEqatu0VGhNSuK SxTLzky6zcfLcwCP6+p6vqYVIiqdgYr4YDh8NQmr37UZIed+N/hp3QVAvHiERE8z P9z/ixzLxQQBtv1Kcxxg7nnRrq4tmGu9qXyX+t/2SNPuXZJ//GWw11m34hEBKkVk Q+2dbz2tEviwlTtFrjCzaPkKZs6T5ftGar8dMn5COUPdiMRQ8Ejm37sqiZx4UcGE 0ERwUDt7DlQoQhIRWvqG7HJ4RUqHrs6+nUH7OjreyDqAyPwe9cx9EkD5KYO2Sx2J 25WNwY6EWINc66J+5WOZB3KGB7ev2KU6YlXPU+vBXA/ZP+5yLTY= =5ToU -----END PGP SIGNATURE----- --p2+YznaeSOZSzEzW--