kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

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 <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/drivers/dma/amd/Kconfig b/drivers/dma/amd/Kconfig
new file mode 100644
index 000000000..00d874872
--- /dev/null
+++ b/drivers/dma/amd/Kconfig
@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+
+config AMD_AE4DMA
+	tristate  "AMD AE4DMA Engine"
+	depends on (X86_64 || COMPILE_TEST) && PCI
+	depends on AMD_PTDMA
+	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
+	help
+	  Enable support for the AMD AE4DMA controller. This controller
+	  provides DMA capabilities to perform high bandwidth memory to
+	  memory and IO copy operations. It performs DMA transfer through
+	  queue-based descriptor management. This DMA controller is intended
+	  to be used with AMD Non-Transparent Bridge devices and not for
+	  general purpose peripheral DMA.
+
+config AMD_PTDMA
+	tristate  "AMD PassThru DMA Engine"
+	depends on X86_64 && PCI
+	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
+	help
+	  Enable support for the AMD PTDMA controller. This controller
+	  provides DMA capabilities to perform high bandwidth memory to
+	  memory and IO copy operations. It performs DMA transfer through
+	  queue-based descriptor management. This DMA controller is intended
+	  to be used with AMD Non-Transparent Bridge devices and not for
+	  general purpose peripheral DMA.
+
+config AMD_QDMA
+	tristate "AMD Queue-based DMA"
+	depends on HAS_IOMEM
+	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
+	select REGMAP_MMIO
+	help
+	  Enable support for the AMD Queue-based DMA subsystem. The primary
+	  mechanism to transfer data using the QDMA is for the QDMA engine to
+	  operate on instructions (descriptors) provided by the host operating
+	  system. Using the descriptors, the QDMA can move data in either the
+	  Host to Card (H2C) direction or the Card to Host (C2H) direction.