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, 110 insertions, 0 deletions

diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
new file mode 100644
index 000000000..5d9bf4694
--- /dev/null
+++ b/Documentation/trace/index.rst
@@ -0,0 +1,110 @@
+================================
+Linux Tracing Technologies Guide
+================================
+
+Tracing in the Linux kernel is a powerful mechanism that allows
+developers and system administrators to analyze and debug system
+behavior. This guide provides documentation on various tracing
+frameworks and tools available in the Linux kernel.
+
+Introduction to Tracing
+-----------------------
+
+This section provides an overview of Linux tracing mechanisms
+and debugging approaches.
+
+.. toctree::
+   :maxdepth: 1
+
+   debugging
+   tracepoints
+   tracepoint-analysis
+   ring-buffer-map
+
+Core Tracing Frameworks
+-----------------------
+
+The following are the primary tracing frameworks integrated into
+the Linux kernel.
+
+.. toctree::
+   :maxdepth: 1
+
+   ftrace
+   ftrace-design
+   ftrace-uses
+   kprobes
+   kprobetrace
+   fprobetrace
+   eprobetrace
+   fprobe
+   ring-buffer-design
+
+Event Tracing and Analysis
+--------------------------
+
+A detailed explanation of event tracing mechanisms and their
+applications.
+
+.. toctree::
+   :maxdepth: 1
+
+   events
+   events-kmem
+   events-power
+   events-nmi
+   events-msr
+   events-pci
+   events-pci-controller
+   boottime-trace
+   histogram
+   histogram-design
+
+Hardware and Performance Tracing
+--------------------------------
+
+This section covers tracing features that monitor hardware
+interactions and system performance.
+
+.. toctree::
+   :maxdepth: 1
+
+   intel_th
+   stm
+   sys-t
+   coresight/index
+   rv/index
+   hisi-ptt
+   mmiotrace
+   hwlat_detector
+   osnoise-tracer
+   timerlat-tracer
+
+User-Space Tracing
+------------------
+
+These tools allow tracing user-space applications and
+interactions.
+
+.. toctree::
+   :maxdepth: 1
+
+   user_events
+   uprobetracer
+
+Remote Tracing
+--------------
+
+This section covers the framework to read compatible ring-buffers, written by
+entities outside of the kernel (most likely firmware or hypervisor)
+
+.. toctree::
+   :maxdepth: 1
+
+   remotes
+
+Additional Resources
+--------------------
+
+For more details, refer to the respective documentation of each
+tracing tool and framework.