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, 113 insertions, 0 deletions

diff --git a/Documentation/gpu/drm-ras.rst b/Documentation/gpu/drm-ras.rst
new file mode 100644
index 000000000..83c21853b
--- /dev/null
+++ b/Documentation/gpu/drm-ras.rst
@@ -0,0 +1,113 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+============================
+DRM RAS over Generic Netlink
+============================
+
+The DRM RAS (Reliability, Availability, Serviceability) interface provides a
+standardized way for GPU/accelerator drivers to expose error counters and
+other reliability nodes to user space via Generic Netlink. This allows
+diagnostic tools, monitoring daemons, or test infrastructure to query hardware
+health in a uniform way across different DRM drivers.
+
+Key Goals:
+
+* Provide a standardized RAS solution for GPU and accelerator drivers, enabling
+  data center monitoring and reliability operations.
+* Implement a single drm-ras Generic Netlink family to meet modern Netlink YAML
+  specifications and centralize all RAS-related communication in one namespace.
+* Support a basic error counter interface, addressing the immediate, essential
+  monitoring needs.
+* Offer a flexible, future-proof interface that can be extended to support
+  additional types of RAS data in the future.
+* Allow multiple nodes per driver, enabling drivers to register separate
+  nodes for different IP blocks, sub-blocks, or other logical subdivisions
+  as applicable.
+
+.. contents::
+
+Nodes
+=====
+
+Nodes are logical abstractions representing an error type or error source within
+the device. Currently, only error counter nodes is supported.
+
+Drivers are responsible for registering and unregistering nodes via the
+`drm_ras_node_register()` and `drm_ras_node_unregister()` APIs.
+
+Node Management
+-------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_ras.c
+   :doc: DRM RAS Node Management
+.. kernel-doc:: drivers/gpu/drm/drm_ras.c
+   :internal:
+
+Generic Netlink Usage
+=====================
+
+The interface is implemented as a Generic Netlink family named ``drm-ras``.
+User space tools can:
+
+* List registered nodes with the ``list-nodes`` command.
+* List all error counters in an node with the ``get-error-counter`` command with ``node-id``
+  as a parameter.
+* Query specific error counter values with the ``get-error-counter`` command, using both
+  ``node-id`` and ``error-id`` as parameters.
+* Clear specific error counters with the ``clear-error-counter`` command, using both
+  ``node-id`` and ``error-id`` as parameters.
+
+YAML-based Interface
+--------------------
+
+The interface is described in a YAML specification ``Documentation/netlink/specs/drm_ras.yaml``
+
+This YAML is used to auto-generate user space bindings via
+``tools/net/ynl/pyynl/ynl_gen_c.py``, and drives the structure of netlink
+attributes and operations.
+
+Usage Notes
+-----------
+
+* User space must first enumerate nodes to obtain their IDs.
+* Node IDs or Node names can be used for all further queries, such as error counters.
+* Error counters can be queried by either the Error ID or Error name.
+* Query Parameters should be defined as part of the uAPI to ensure user interface stability.
+* The interface supports future extension by adding new node types and
+  additional attributes.
+
+Example: List nodes using ynl
+
+.. code-block:: bash
+
+    sudo ynl --family drm_ras --dump list-nodes
+    [{'device-name': '0000:03:00.0',
+    'node-id': 0,
+    'node-name': 'correctable-errors',
+    'node-type': 'error-counter'},
+    {'device-name': '0000:03:00.0',
+     'node-id': 1,
+     'node-name': 'uncorrectable-errors',
+     'node-type': 'error-counter'}]
+
+Example: List all error counters using ynl
+
+.. code-block:: bash
+
+    sudo ynl --family drm_ras --dump get-error-counter --json '{"node-id":0}'
+    [{'error-id': 1, 'error-name': 'error_name1', 'error-value': 0},
+    {'error-id': 2, 'error-name': 'error_name2', 'error-value': 0}]
+
+Example: Query an error counter for a given node
+
+.. code-block:: bash
+
+    sudo ynl --family drm_ras --do get-error-counter --json '{"node-id":0, "error-id":1}'
+    {'error-id': 1, 'error-name': 'error_name1', 'error-value': 0}
+
+Example: Clear an error counter for a given node
+
+.. code-block:: bash
+
+    sudo ynl --family drm_ras --do clear-error-counter --json '{"node-id":0, "error-id":1}'
+    None