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, 138 insertions, 0 deletions

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
new file mode 100644
index 000000000..9f81af350
--- /dev/null
+++ b/drivers/video/console/Kconfig
@@ -0,0 +1,138 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Video configuration
+#
+
+menu "Console display driver support"
+
+config VGA_CONSOLE
+	bool "VGA text console" if EXPERT || !X86
+	depends on ALPHA || X86 || \
+		(ARM && ARCH_FOOTBRIDGE) || \
+		(MIPS && (MIPS_MALTA || SIBYTE_BCM112X || SIBYTE_SB1250 || SIBYTE_BCM1x80 || SNI_RM))
+	select APERTURE_HELPERS if (DRM || FB || VFIO_PCI_CORE)
+	default y
+	help
+	  Saying Y here will allow you to use Linux in text mode through a
+	  display that complies with the generic VGA standard. Virtually
+	  everyone wants that.
+
+	  The program SVGATextMode can be used to utilize SVGA video cards to
+	  their full potential in text mode. Download it from
+	  <ftp://ibiblio.org/pub/Linux/utils/console/>.
+
+	  Say Y.
+
+config SGI_NEWPORT_CONSOLE
+	tristate "SGI Newport Console support"
+	depends on SGI_IP22 && HAS_IOMEM
+	select FONT_SUPPORT
+	help
+	  Say Y here if you want the console on the Newport aka XL graphics
+	  card of your Indy.  Most people say Y here.
+
+config DUMMY_CONSOLE
+	def_bool VT || VGA_CONSOLE || FRAMEBUFFER_CONSOLE
+
+config DUMMY_CONSOLE_COLUMNS
+	int "Initial number of console screen columns"
+	depends on DUMMY_CONSOLE && !(ARCH_FOOTBRIDGE && VGA_CONSOLE)
+	default 160 if PARISC
+	default 80
+	help
+	  On PA-RISC, the default value is 160, which should fit a 1280x1024
+	  monitor.
+	  Select 80 if you use a 640x480 resolution by default.
+
+config DUMMY_CONSOLE_ROWS
+	int "Initial number of console screen rows"
+	depends on DUMMY_CONSOLE && !(ARCH_FOOTBRIDGE && VGA_CONSOLE)
+	default 64 if PARISC
+	default 30 if ARM
+	default 25
+	help
+	  On PA-RISC, the default value is 64, which should fit a 1280x1024
+	  monitor.
+	  Select 25 if you use a 640x480 resolution by default.
+
+config FRAMEBUFFER_CONSOLE
+	bool "Framebuffer Console support"
+	depends on FB_CORE && !UML
+	default DRM_FBDEV_EMULATION
+	select VT_HW_CONSOLE_BINDING
+	select CRC32
+	select FONT_SUPPORT
+	help
+	  Low-level framebuffer-based console driver.
+
+config FRAMEBUFFER_CONSOLE_LEGACY_ACCELERATION
+	bool "Enable legacy fbcon hardware acceleration code"
+	depends on FRAMEBUFFER_CONSOLE
+	default y if PARISC
+	default n
+	help
+	  This option enables the fbcon (framebuffer text-based) hardware
+	  acceleration for graphics drivers which were written for the fbdev
+	  graphics interface.
+
+	  On modern machines, on mainstream machines (like x86-64) or when
+	  using a modern Linux distribution those fbdev drivers usually aren't used.
+	  So enabling this option wouldn't have any effect, which is why you want
+	  to disable this option on such newer machines.
+
+	  If you compile this kernel for older machines which still require the
+	  fbdev drivers, you may want to say Y.
+
+	  If unsure, select n.
+
+config FRAMEBUFFER_CONSOLE_DETECT_PRIMARY
+       bool "Map the console to the primary display device"
+       depends on FRAMEBUFFER_CONSOLE
+       default n
+	help
+	 If this option is selected, the framebuffer console will
+	 automatically select the primary display device (if the architecture
+	 supports this feature).  Otherwise, the framebuffer console will
+	 always select the first framebuffer driver that is loaded. The latter
+	 is the default behavior.
+
+	 You can always override the automatic selection of the primary device
+	 by using the fbcon=map: boot option.
+
+	 If unsure, select n.
+
+config FRAMEBUFFER_CONSOLE_ROTATION
+       bool "Framebuffer Console Rotation"
+       depends on FRAMEBUFFER_CONSOLE
+       help
+	 Enable display rotation for the framebuffer console.  This is done
+	 in software and may be significantly slower than a normally oriented
+	 display.  Note that the rotation is done at the console level only
+	 such that other users of the framebuffer will remain normally
+	 oriented.
+
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+	bool "Framebuffer Console Deferred Takeover"
+	depends on FB=y && FRAMEBUFFER_CONSOLE && DUMMY_CONSOLE
+	help
+	  If enabled this defers the framebuffer console taking over the
+	  console from the dummy console until the first text is displayed on
+	  the console. This is useful in combination with the "quiet" kernel
+	  commandline option to keep the framebuffer contents initially put up
+	  by the firmware in place, rather then replacing the contents with a
+	  black screen as soon as fbcon loads.
+
+config STI_CONSOLE
+	bool "STI text console"
+	depends on PARISC && HAS_IOMEM
+	select FONT_SUPPORT
+	select CRC32
+	select STI_CORE
+	default y
+	help
+	  The STI console is the builtin display/keyboard on HP-PARISC
+	  machines.  Say Y here to build support for it into your kernel.
+	  The alternative is to use your primary serial port as a console.
+
+endmenu
+