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[118.211.5.80]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7080256c9dcsm13025732b3a.74.2024.07.04.21.40.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Jul 2024 21:40:30 -0700 (PDT) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 05 Jul 2024 14:40:19 +1000 Message-Id: Cc: "Peter Maydell" , "Akihiko Odaki" , "Eduardo Habkost" , "Marcel Apfelbaum" , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , "Yanan Wang" , "John Snow" , "BALATON Zoltan" , "Jiaxun Yang" , "Daniel Henrique Barboza" , "Harsh Prateek Bora" , "Alexey Kardashevskiy" , "Michael S. Tsirkin" , =?utf-8?q?Alex_Benn=C3=A9e?= , "Peter Xu" , "Fabiano Rosas" , "Paolo Bonzini" , "David Hildenbrand" , "Thomas Huth" , "Laurent Vivier" , , , Subject: Re: [PATCH v2 06/15] ppc/vof: Fix unaligned FDT property access From: "Nicholas Piggin" To: "David Gibson" X-Mailer: aerc 0.17.0 References: <20240627-san-v2-0-750bb0946dbd@daynix.com> <20240627-san-v2-6-750bb0946dbd@daynix.com> In-Reply-To: Received-SPF: pass client-ip=2607:f8b0:4864:20::1129; envelope-from=npiggin@gmail.com; helo=mail-yw1-x1129.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri Jul 5, 2024 at 11:41 AM AEST, David Gibson wrote: > On Fri, Jul 05, 2024 at 11:18:47AM +1000, Nicholas Piggin wrote: > > On Thu Jul 4, 2024 at 10:15 PM AEST, Peter Maydell wrote: > > > On Sat, 29 Jun 2024 at 04:17, David Gibson wrote: > > > > > > > > On Fri, Jun 28, 2024 at 04:20:02PM +0100, Peter Maydell wrote: > > > > > On Thu, 27 Jun 2024 at 14:39, Akihiko Odaki wrote: > > > > > > > > > > > > FDT properties are aligned by 4 bytes, not 8 bytes. > > > > > > > > > > > > Signed-off-by: Akihiko Odaki > > > > > > --- > > > > > > hw/ppc/vof.c | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c > > > > > > index e3b430a81f4f..b5b6514d79fc 100644 > > > > > > --- a/hw/ppc/vof.c > > > > > > +++ b/hw/ppc/vof.c > > > > > > @@ -646,7 +646,7 @@ static void vof_dt_memory_available(void *f= dt, GArray *claimed, uint64_t base) > > > > > > mem0_reg =3D fdt_getprop(fdt, offset, "reg", &proplen); > > > > > > g_assert(mem0_reg && proplen =3D=3D sizeof(uint32_t) * (ac= + sc)); > > > > > > if (sc =3D=3D 2) { > > > > > > - mem0_end =3D be64_to_cpu(*(uint64_t *)(mem0_reg + size= of(uint32_t) * ac)); > > > > > > + mem0_end =3D ldq_be_p(mem0_reg + sizeof(uint32_t) * ac= ); > > > > > > } else { > > > > > > mem0_end =3D be32_to_cpu(*(uint32_t *)(mem0_reg + size= of(uint32_t) * ac)); > > > > > > } > > > > > > > > > > I did wonder if there was a better way to do what this is doing, > > > > > but neither we (in system/device_tree.c) nor libfdt seem to > > > > > provide one. > > > > > > > > libfdt does provide unaligned access helpers (fdt32_ld() etc.), but > > > > not an automatic aligned-or-unaligned helper. Maybe we should add= that? > > > > > > fdt32_ld() and friends only do the "load from this bit of memory" > > > part, which we already have QEMU utility functions for (and which > > > are this patch uses). > > > > > > This particular bit of code is dealing with an fdt property ("memory"= ) > > > that is an array of (address, size) tuples where address and size > > > can independently be either 32 or 64 bits, and it wants the > > > size value of tuple 0. So the missing functionality is something at > > > a higher level than fdt32_ld() which would let you say "give me > > > tuple N field X" with some way to specify the tuple layout. (Which > > > is an awkward kind of API to write in C.) > > > > > > Slightly less general, but for this case we could perhaps have > > > something like the getprop equivalent of qemu_fdt_setprop_sized_cells= (): > > > > > > uint64_t value_array[2]; > > > qemu_fdt_getprop_sized_cells(fdt, nodename, "memory", &value_array, > > > ac, sc); > > > /* > > > * fills in value_array[0] with address, value_array[1] with size, > > > * probably barfs if the varargs-list of cell-sizes doesn't > > > * cover the whole property, similar to the current assert on > > > * proplen. > > > */ > > > mem0_end =3D value_array[0]; > >=20 > > Since 4/8 byte cells are most common and size is probably > > normally known, what about something simpler to start with? > > Hrm, I don't think this helps much. As Peter points out the actual > load isn't really the issue, it's locating the right spot for it. I don't really see why that's a problem, it's just a pointer addition - base + fdt_address_cells * 4. The problem was in the memory access (yes it's fixed with the patch but you could add a general libfdt way to do it). Some fancy function like above could be used, But is it really worth implementing such a thing for this? Thanks, Nick