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, 204 insertions, 0 deletions

diff --git a/Documentation/fb/sstfb.rst b/Documentation/fb/sstfb.rst
new file mode 100644
index 000000000..7386eb63b
--- /dev/null
+++ b/Documentation/fb/sstfb.rst
@@ -0,0 +1,204 @@
+=====
+sstfb
+=====
+
+Introduction
+============
+
+This is a frame buffer device driver for 3dfx' Voodoo Graphics
+(aka voodoo 1, aka sst1) and Voodoo² (aka Voodoo 2, aka CVG) based
+video boards. It's highly experimental code, but is guaranteed to work
+on my computer, with my "Maxi Gamer 3D" and "Maxi Gamer 3d²" boards,
+and with me "between chair and keyboard". Some people tested other
+combinations and it seems that it works.
+The main page is located at <http://sstfb.sourceforge.net>, and if
+you want the latest version, check out the CVS, as the driver is a work
+in progress, I feel uncomfortable with releasing tarballs of something
+not completely working...Don't worry, it's still more than usable
+(I eat my own dog food)
+
+Please read the Bug section, and report any success or failure to me
+(Ghozlane Toumi <gtoumi@laposte.net>).
+BTW, If you have only one monitor , and you don't feel like playing
+with the vga passthrou cable, I can only suggest borrowing a screen
+somewhere...
+
+
+Installation
+============
+
+This driver (should) work on ix86, with "late" 2.2.x kernel (tested
+with x = 19) and "recent" 2.4.x kernel, as a module or compiled in.
+It has been included in mainstream kernel since the infamous 2.4.10.
+You can apply the patches found in `sstfb/kernel/*-2.{2|4}.x.patch`,
+and copy sstfb.c to linux/drivers/video/, or apply a single patch,
+`sstfb/patch-2.{2|4}.x-sstfb-yymmdd` to your linux source tree.
+
+Then configure your kernel as usual: choose "m" or "y" to 3Dfx Voodoo
+Graphics in section "console". Compile, install, have fun... and please
+drop me a report :)
+
+
+Module Usage
+============
+
+.. warning::
+
+       #. You should read completely this section before issuing any command.
+
+       #. If you have only one monitor to play with, once you insmod the
+	  module, the 3dfx takes control of the output, so you'll have to
+	  plug the monitor to the "normal" video board in order to issue
+	  the commands, or you can blindly use sst_dbg_vgapass
+	  in the tools directory (See Tools). The latest solution is pass the
+	  parameter vgapass=1 when insmodding the driver. (See Kernel/Modules
+	  Options)
+
+Module insertion
+----------------
+
+       #. insmod sstfb.o
+
+	  you should see some strange output from the board:
+	  a big blue square, a green and a red small squares and a vertical
+	  white rectangle. why? the function's name is self-explanatory:
+	  "sstfb_test()"...
+	  (if you don't have a second monitor, you'll have to plug your monitor
+	  directly to the 2D videocard to see what you're typing)
+
+       #. con2fb /dev/fbx /dev/ttyx
+
+	  bind a tty to the new frame buffer. if you already have a frame
+	  buffer driver, the voodoo fb will likely be /dev/fb1. if not,
+	  the device will be /dev/fb0. You can check this by doing a
+	  cat /proc/fb. You can find a copy of con2fb in tools/ directory.
+	  if you don't have another fb device, this step is superfluous,
+	  as the console subsystem automagically binds ttys to the fb.
+       #. switch to the virtual console you just mapped. "tadaaa" ...
+
+Module removal
+--------------
+
+       #. con2fb /dev/fbx /dev/ttyx
+
+	  bind the tty to the old frame buffer so the module can be removed.
+	  (how does it work with vgacon ? short answer : it doesn't work)
+
+       #. rmmod sstfb
+
+
+Kernel/Modules Options
+----------------------
+
+You can pass some options to the sstfb module, and via the kernel
+command line when the driver is compiled in:
+for module : insmod sstfb.o option1=value1 option2=value2 ...
+in kernel :  video=sstfb:option1,option2:value2,option3 ...
+
+sstfb supports the following options:
+
+=============== =============== ===============================================
+Module		Kernel		Description
+=============== =============== ===============================================
+vgapass=0	vganopass	Enable or disable VGA passthrou cable.
+vgapass=1	vgapass		When enabled, the monitor will get the signal
+				from the VGA board and not from the voodoo.
+
+				Default: nopass
+
+mem=x		mem:x		Force frame buffer memory in MiB
+				allowed values: 0, 1, 2, 4.
+
+				Default: 0 (= autodetect)
+
+inverse=1	inverse		Supposed to enable inverse console.
+				doesn't work yet...
+
+clipping=1	clipping	Enable or disable clipping.
+clipping=0	noclipping	With clipping enabled, all offscreen
+				reads and writes are discarded.
+
+				Default: enable clipping.
+
+gfxclk=x	gfxclk:x	Force graphic clock frequency (in MHz).
+				Be careful with this option, it may be
+				DANGEROUS.
+
+				Default: auto
+
+					- 50Mhz for Voodoo 1,
+					- 75MHz for Voodoo 2.
+
+slowpci=1	fastpci		Enable or disable fast PCI read/writes.
+slowpci=1	slowpci		Default : fastpci
+
+dev=x		dev:x		Attach the driver to device number x.
+				0 is the first compatible board (in
+				lspci order)
+=============== =============== ===============================================
+
+Tools
+=====
+
+These tools are mostly for debugging purposes, but you can
+find some of these interesting:
+
+- `con2fb`, maps a tty to a fbramebuffer::
+
+	con2fb /dev/fb1 /dev/tty5
+
+- `sst_dbg_vgapass`, changes vga passthrou. You have to recompile the
+  driver with SST_DEBUG and SST_DEBUG_IOCTL set to 1::
+
+	sst_dbg_vgapass /dev/fb1 1 (enables vga cable)
+	sst_dbg_vgapass /dev/fb1 0 (disables vga cable)
+
+- `glide_reset`, resets the voodoo using glide
+  use this after rmmoding sstfb, if the module refuses to
+  reinsert.
+
+Bugs
+====
+
+- DO NOT use glide while the sstfb module is in, you'll most likely
+  hang your computer.
+- If you see some artefacts (pixels not cleaning and stuff like that),
+  try turning off clipping (clipping=0), and/or using slowpci
+- the driver don't detect the 4Mb frame buffer voodoos, it seems that
+  the 2 last Mbs wrap around. looking into that .
+- The driver is 16 bpp only, 24/32 won't work.
+- The driver is not your_favorite_toy-safe. this includes SMP...
+
+	[Actually from inspection it seems to be safe - Alan]
+
+- When using XFree86 FBdev (X over fbdev) you may see strange color
+  patterns at the border of your windows (the pixels lose the lowest
+  byte -> basically the blue component and some of the green). I'm unable
+  to reproduce this with XFree86-3.3, but one of the testers has this
+  problem with XFree86-4. Apparently recent Xfree86-4.x solve this
+  problem.
+- I didn't really test changing the palette, so you may find some weird
+  things when playing with that.
+- Sometimes the driver will not recognise the DAC, and the
+  initialisation will fail. This is specifically true for
+  voodoo 2 boards, but it should be solved in recent versions. Please
+  contact me.
+- The 24/32 is not likely to work anytime soon, knowing that the
+  hardware does ... unusual things in 24/32 bpp.
+
+Todo
+====
+
+- Get rid of the previous paragraph.
+- Buy more coffee.
+- test/port to other arch.
+- try to add panning using tweaks with front and back buffer.
+- try to implement accel on voodoo2, this board can actually do a
+  lot in 2D even if it was sold as a 3D only board ...
+
+Ghozlane Toumi <gtoumi@laposte.net>
+
+
+Date: 2002/05/09 20:11:45
+
+http://sstfb.sourceforge.net/README