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, 159 insertions, 0 deletions

diff --git a/lib/fonts/Kconfig b/lib/fonts/Kconfig
new file mode 100644
index 000000000..7d03823e4
--- /dev/null
+++ b/lib/fonts/Kconfig
@@ -0,0 +1,159 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Font configuration
+#
+
+config FONT_SUPPORT
+	tristate
+
+if FONT_SUPPORT
+
+config FONTS
+	bool "Select compiled-in fonts"
+	depends on FRAMEBUFFER_CONSOLE || STI_CONSOLE || DRM_PANIC || DRM_CLIENT_LOG
+	help
+	  Say Y here if you would like to use fonts other than the default
+	  your frame buffer console usually use.
+
+	  Note that the answer to this question won't directly affect the
+	  kernel: saying N will just cause the configurator to skip all
+	  the questions about foreign fonts.
+
+	  If unsure, say N (the default choices are safe).
+
+config FONT_8x8
+	bool "VGA 8x8 font" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || STI_CONSOLE || DRM_PANIC
+	default y if !SPARC && !FONTS
+	help
+	  This is the "high resolution" font for the VGA frame buffer (the one
+	  provided by the text console 80x50 (and higher) modes).
+
+	  Note that this is a poor quality font. The VGA 8x16 font is quite a
+	  lot more readable.
+
+	  Given the resolution provided by the frame buffer device, answer N
+	  here is safe.
+
+config FONT_8x16
+	bool "VGA 8x16 font" if FONTS
+	default y if !SPARC && !FONTS
+	help
+	  This is the "high resolution" font for the VGA frame buffer (the one
+	  provided by the VGA text console 80x25 mode.
+
+	  If unsure, say Y.
+
+config FONT_6x11
+	bool "Mac console 6x11 font (not supported by all drivers)" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || STI_CONSOLE || DRM_PANIC
+	default y if !SPARC && !FONTS && MAC
+	help
+	  Small console font with Macintosh-style high-half glyphs.  Some Mac
+	  framebuffer drivers don't support this one at all.
+
+config FONT_7x14
+	bool "console 7x14 font (not supported by all drivers)" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	help
+	  Console font with characters just a bit smaller than the default.
+	  If the standard 8x16 font is a little too big for you, say Y.
+	  Otherwise, say N.
+
+config FONT_PEARL_8x8
+	bool "Pearl (old m68k) console 8x8 font" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	default y if !SPARC && !FONTS && AMIGA
+	help
+	  Small console font with PC-style control-character and high-half
+	  glyphs.
+
+config FONT_ACORN_8x8
+	bool "Acorn console 8x8 font" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	default y if !SPARC && !FONTS && ARM && ARCH_ACORN
+	help
+	  Small console font with PC-style control characters and high-half
+	  glyphs.
+
+config FONT_MINI_4x6
+	bool "Mini 4x6 font"
+	depends on !SPARC && FONTS
+
+config FONT_6x10
+	bool "Medium-size 6x10 font"
+	depends on !SPARC && FONTS
+	help
+	  Medium-size console font. Suitable for framebuffer consoles on
+	  embedded devices with a 320x240 screen, to get a reasonable number
+	  of characters (53x24) that are still at a readable size.
+
+config FONT_10x18
+	bool "console 10x18 font (not supported by all drivers)" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	help
+	  This is a high resolution console font for machines with very
+	  big letters. It fits between the sun 12x22 and the normal 8x16 font.
+	  If other fonts are too big or too small for you, say Y, otherwise say N.
+
+config FONT_SUN8x16
+	bool "Sparc console 8x16 font"
+	depends on (FRAMEBUFFER_CONSOLE && (FONTS || SPARC)) || \
+		   BOOTX_TEXT || EARLYFB
+	help
+	  This is the high resolution console font for Sun machines. Say Y.
+
+config FONT_SUN12x22
+	bool "Sparc console 12x22 font (not supported by all drivers)"
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	depends on !SPARC && FONTS
+	help
+	  This is the high resolution console font for Sun machines with very
+	  big letters (like the letters used in the SPARC PROM). If the
+	  standard font is unreadable for you, say Y, otherwise say N.
+
+config FONT_TER10x18
+	bool "Terminus 10x18 font (not supported by all drivers)"
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	depends on !SPARC && FONTS || SPARC
+	help
+	  Terminus Font is a clean, fixed width bitmap font, designed
+	  for long (8 and more hours per day) work with computers.
+	  This is the high resolution version made for use with 13-16" laptops.
+	  It fits between the normal 8x16 font and Terminus 16x32.
+	  If other fonts are unreadable for you, say Y, otherwise say N.
+
+config FONT_TER16x32
+	bool "Terminus 16x32 font (not supported by all drivers)"
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	depends on !SPARC && FONTS || SPARC
+	help
+	  Terminus Font is a clean, fixed width bitmap font, designed
+	  for long (8 and more hours per day) work with computers.
+	  This is the high resolution, large version for use with HiDPI screens.
+	  If the standard font is unreadable for you, say Y, otherwise say N.
+
+config FONT_6x8
+	bool "OLED 6x8 font" if FONTS
+	depends on FRAMEBUFFER_CONSOLE || DRM_PANIC
+	help
+	  This font is useful for small displays (OLED).
+
+config FONT_AUTOSELECT
+	def_bool y
+	depends on !FONT_8x8
+	depends on !FONT_6x11
+	depends on !FONT_7x14
+	depends on !FONT_PEARL_8x8
+	depends on !FONT_ACORN_8x8
+	depends on !FONT_MINI_4x6
+	depends on !FONT_6x10
+	depends on !FONT_SUN8x16
+	depends on !FONT_SUN12x22
+	depends on !FONT_10x18
+	depends on !FONT_TER10x18
+	depends on !FONT_TER16x32
+	depends on !FONT_6x8
+	select FONT_8x16
+
+endif # FONT_SUPPORT