From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit `objtool` errors such as: vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a: can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd The reason is that in such builds, the Clang invocation that compiles the combined Rust plus helpers bitcode emits LLVM bitcode (again) -- the final code generation happens in the linker's LTO step, which the `-mllvm` trap options passed to Clang do not reach. This, in turn, means that unreachable traps are missing, and the impossible paths do not merely fallthrough to the next symbol, but past the end of their own section, since LTO builds place each function in its own section. Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always emits machine code directly, with the traps in place. Assisted-by: LLM Cc: Gary Guo Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- samples/vfio-mdev/README.rst | 100 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 100 insertions(+) create mode 100644 samples/vfio-mdev/README.rst (limited to 'samples/vfio-mdev/README.rst') diff --git a/samples/vfio-mdev/README.rst b/samples/vfio-mdev/README.rst new file mode 100644 index 000000000..b52eb3773 --- /dev/null +++ b/samples/vfio-mdev/README.rst @@ -0,0 +1,100 @@ +Using the mtty vfio-mdev sample code +==================================== + +mtty is a sample vfio-mdev driver that demonstrates how to use the mediated +device framework. + +The sample driver creates an mdev device that simulates a serial port over a PCI +card. + +1. Build and load the mtty.ko module. + + This step creates a dummy device, /sys/devices/virtual/mtty/mtty/ + + Files in this device directory in sysfs are similar to the following:: + + # tree /sys/devices/virtual/mtty/mtty/ + /sys/devices/virtual/mtty/mtty/ + |-- mdev_supported_types + | |-- mtty-1 + | | |-- available_instances + | | |-- create + | | |-- device_api + | | |-- devices + | | `-- name + | `-- mtty-2 + | |-- available_instances + | |-- create + | |-- device_api + | |-- devices + | `-- name + |-- mtty_dev + | `-- sample_mtty_dev + |-- power + | |-- autosuspend_delay_ms + | |-- control + | |-- runtime_active_time + | |-- runtime_status + | `-- runtime_suspended_time + |-- subsystem -> ../../../../class/mtty + `-- uevent + +2. Create a mediated device by using the dummy device that you created in the + previous step:: + + # echo "83b8f4f2-509f-382f-3c1e-e6bfe0fa1001" > \ + /sys/devices/virtual/mtty/mtty/mdev_supported_types/mtty-2/create + +3. Add parameters to qemu-kvm:: + + -device vfio-pci,\ + sysfsdev=/sys/bus/mdev/devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1001 + +4. Boot the VM. + + In the Linux guest VM, with no hardware on the host, the device appears + as follows:: + + # lspci -s 00:05.0 -xxvv + 00:05.0 Serial controller: Device 4348:3253 (rev 10) (prog-if 02 [16550]) + Subsystem: Device 4348:3253 + Physical Slot: 5 + Control: I/O+ Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- + Stepping- SERR- FastB2B- DisINTx- + Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort- + SERR- Link[LNKA] -> GSI 10 (level, high) -> IRQ 10 + 0000:00:05.0: ttyS1 at I/O 0xc150 (irq = 10) is a 16550A + 0000:00:05.0: ttyS2 at I/O 0xc158 (irq = 10) is a 16550A + + +5. In the Linux guest VM, check the serial ports:: + + # setserial -g /dev/ttyS* + /dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4 + /dev/ttyS1, UART: 16550A, Port: 0xc150, IRQ: 10 + /dev/ttyS2, UART: 16550A, Port: 0xc158, IRQ: 10 + +6. Using minicom or any terminal emulation program, open port /dev/ttyS1 or + /dev/ttyS2 with hardware flow control disabled. + +7. Type data on the minicom terminal or send data to the terminal emulation + program and read the data. + + Data is loop backed from hosts mtty driver. + +8. Destroy the mediated device that you created:: + + # echo 1 > /sys/bus/mdev/devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1001/remove + -- cgit v1.3.1