| Message ID | 20250320133248.1679485-3-peter.maydell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | rust: Fix PL011State size mismatch assert | expand |
On Thu, Mar 20, 2025 at 01:32:47PM +0000, Peter Maydell wrote: > Date: Thu, 20 Mar 2025 13:32:47 +0000 > From: Peter Maydell <peter.maydell@linaro.org> > Subject: [PATCH 2/3] hw/char/pl011: Pad PL011State struct to same size as > Rust impl > X-Mailer: git-send-email 2.43.0 > > We have some users of the PL011 struct which embed it directly into > their own state structs. This means that the Rust version of the > device must have a state struct that is the same size or smaller > than the C struct. > > In commit 9b642097d6b7 ("rust: pl011: switch to safe chardev operation") > the Rust PL011 state struct changed from having a bindings::CharBackend > to a chardev::CharBackend, which made it grow larger than the C > version. This results in an assertion at startup when QEMU was > built with Rust enabled: > > $ qemu-system-arm -M raspi2b -display none > ERROR:../../qom/object.c:562:object_initialize_with_type: assertion > failed: (size >= type->instance_size) > > The long-term better approach to this problem would be to move > our C device code patterns away from "embed a struct" and (back) > to "have a pointer to the device", so we can make the C PL011State > struct a private implementation detail rather than exposed to > its users. > > For the short term, add a padding field at the end of the C struct > so it's big enough that the Rust state struct can fit. > > Fixes: 9b642097d6b7 ("rust: pl011: switch to safe chardev operation") > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > include/hw/char/pl011.h | 5 +++++ > 1 file changed, 5 insertions(+) LGTM, BqlRefCell<> has extra fields to make BqlRefCell<T> bigger than T, Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
diff --git a/include/hw/char/pl011.h b/include/hw/char/pl011.h index 4fcaf3d7d30..299ca9b18bb 100644 --- a/include/hw/char/pl011.h +++ b/include/hw/char/pl011.h @@ -52,6 +52,11 @@ struct PL011State { Clock *clk; bool migrate_clk; const unsigned char *id; + /* + * Since some users embed this struct directly, we must + * ensure that the C struct is at least as big as the Rust one. + */ + uint8_t padding_for_rust[16]; }; DeviceState *pl011_create(hwaddr addr, qemu_irq irq, Chardev *chr);
We have some users of the PL011 struct which embed it directly into their own state structs. This means that the Rust version of the device must have a state struct that is the same size or smaller than the C struct. In commit 9b642097d6b7 ("rust: pl011: switch to safe chardev operation") the Rust PL011 state struct changed from having a bindings::CharBackend to a chardev::CharBackend, which made it grow larger than the C version. This results in an assertion at startup when QEMU was built with Rust enabled: $ qemu-system-arm -M raspi2b -display none ERROR:../../qom/object.c:562:object_initialize_with_type: assertion failed: (size >= type->instance_size) The long-term better approach to this problem would be to move our C device code patterns away from "embed a struct" and (back) to "have a pointer to the device", so we can make the C PL011State struct a private implementation detail rather than exposed to its users. For the short term, add a padding field at the end of the C struct so it's big enough that the Rust state struct can fit. Fixes: 9b642097d6b7 ("rust: pl011: switch to safe chardev operation") Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- include/hw/char/pl011.h | 5 +++++ 1 file changed, 5 insertions(+)