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, 107 insertions, 0 deletions

diff --git a/Documentation/admin-guide/sysctl/index.rst b/Documentation/admin-guide/sysctl/index.rst
new file mode 100644
index 000000000..50f00514f
--- /dev/null
+++ b/Documentation/admin-guide/sysctl/index.rst
@@ -0,0 +1,107 @@
+===========================
+Documentation for /proc/sys
+===========================
+
+Copyright (c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>
+
+------------------------------------------------------------------------------
+
+'Why', I hear you ask, 'would anyone even _want_ documentation
+for them sysctl files? If anybody really needs it, it's all in
+the source...'
+
+Well, this documentation is written because some people either
+don't know they need to tweak something, or because they don't
+have the time or knowledge to read the source code.
+
+Furthermore, the programmers who built sysctl have built it to
+be actually used, not just for the fun of programming it :-)
+
+------------------------------------------------------------------------------
+
+Legal blurb:
+
+As usual, there are two main things to consider:
+
+1. you get what you pay for
+2. it's free
+
+The consequences are that I won't guarantee the correctness of
+this document, and if you come to me complaining about how you
+screwed up your system because of wrong documentation, I won't
+feel sorry for you. I might even laugh at you...
+
+But of course, if you _do_ manage to screw up your system using
+only the sysctl options used in this file, I'd like to hear of
+it. Not only to have a great laugh, but also to make sure that
+you're the last RTFMing person to screw up.
+
+In short, e-mail your suggestions, corrections and / or horror
+stories to: <riel@nl.linux.org>
+
+Rik van Riel.
+
+--------------------------------------------------------------
+
+Introduction
+============
+
+Sysctl is a means of configuring certain aspects of the kernel
+at run-time, and the /proc/sys/ directory is there so that you
+don't even need special tools to do it!
+In fact, there are only four things needed to use these config
+facilities:
+
+- a running Linux system
+- root access
+- common sense (this is especially hard to come by these days)
+- knowledge of what all those values mean
+
+As a quick 'ls /proc/sys' will show, the directory consists of
+several (arch-dependent?) subdirs. Each subdir is mainly about
+one part of the kernel, so you can do configuration on a piece
+by piece basis, or just some 'thematic frobbing'.
+
+This documentation is about:
+
+=============== ===============================================================
+abi/		execution domains & personalities
+<$ARCH>		tuning controls for various CPU architecture (e.g. csky, s390)
+crypto/		cryptographic subsystem
+debug/		debugging features
+dev/		device specific information (e.g. dev/cdrom/info)
+fs/		specific filesystems
+		filehandle, inode, dentry and quota tuning
+		binfmt_misc <Documentation/admin-guide/binfmt-misc.rst>
+kernel/		global kernel info / tuning
+		miscellaneous stuff
+		some architecture-specific controls
+		security (LSM) stuff
+net/		networking stuff, for documentation look in:
+		<Documentation/networking/>
+proc/		<empty>
+sunrpc/		SUN Remote Procedure Call (NFS)
+user/		Per user namespace limits
+vm/		memory management tuning
+		buffer and cache management
+xen/		Xen hypervisor controls
+=============== ===============================================================
+
+These are the subdirs I have on my system or have been discovered by
+searching through the source code. There might be more or other subdirs
+in another setup. If you see another dir, I'd really like to hear about
+it :-)
+
+.. toctree::
+   :maxdepth: 1
+
+   abi
+   crypto
+   debug
+   fs
+   kernel
+   net
+   sunrpc
+   user
+   vm
+   xen