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, 227 insertions, 0 deletions

diff --git a/drivers/mtd/devices/Kconfig b/drivers/mtd/devices/Kconfig
new file mode 100644
index 000000000..e518dfeee
--- /dev/null
+++ b/drivers/mtd/devices/Kconfig
@@ -0,0 +1,227 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "Self-contained MTD device drivers"
+	depends on MTD!=n
+	depends on HAS_IOMEM
+
+config MTD_PMC551
+	tristate "Ramix PMC551 PCI Mezzanine RAM card support"
+	depends on PCI
+	help
+	  This provides a MTD device driver for the Ramix PMC551 RAM PCI card
+	  from Ramix Inc. <http://www.ramix.com/products/memory/pmc551.html>.
+	  These devices come in memory configurations from 32M - 1G.  If you
+	  have one, you probably want to enable this.
+
+	  If this driver is compiled as a module you get the ability to select
+	  the size of the aperture window pointing into the devices memory.
+	  What this means is that if you have a 1G card, normally the kernel
+	  will use a 1G memory map as its view of the device.  As a module,
+	  you can select a 1M window into the memory and the driver will
+	  "slide" the window around the PMC551's memory.  This was
+	  particularly useful on the 2.2 kernels on PPC architectures as there
+	  was limited kernel space to deal with.
+
+config MTD_PMC551_BUGFIX
+	bool "PMC551 256M DRAM Bugfix"
+	depends on MTD_PMC551
+	help
+	  Some of Ramix's PMC551 boards with 256M configurations have invalid
+	  column and row mux values.  This option will fix them, but will
+	  break other memory configurations.  If unsure say N.
+
+config MTD_PMC551_DEBUG
+	bool "PMC551 Debugging"
+	depends on MTD_PMC551
+	help
+	  This option makes the PMC551 more verbose during its operation and
+	  is only really useful if you are developing on this driver or
+	  suspect a possible hardware or driver bug.  If unsure say N.
+
+config MTD_MS02NV
+	tristate "DEC MS02-NV NVRAM module support"
+	depends on MACH_DECSTATION
+	help
+	  This is an MTD driver for the DEC's MS02-NV (54-20948-01) battery
+	  backed-up NVRAM module.  The module was originally meant as an NFS
+	  accelerator.  Say Y here if you have a DECstation 5000/2x0 or a
+	  DECsystem 5900 equipped with such a module.
+
+	  If you want to compile this driver as a module ( = code which can be
+	  inserted in and removed from the running kernel whenever you want),
+	  say M here and read <file:Documentation/kbuild/modules.rst>.
+	  The module will be called ms02-nv.
+
+config MTD_DATAFLASH
+	tristate "Support for AT45xxx DataFlash"
+	depends on SPI_MASTER
+	help
+	  This enables access to AT45xxx DataFlash chips, using SPI.
+	  Sometimes DataFlash chips are packaged inside MMC-format
+	  cards; at this writing, the MMC stack won't handle those.
+
+config MTD_DATAFLASH_WRITE_VERIFY
+	bool "Verify DataFlash page writes"
+	depends on MTD_DATAFLASH
+	help
+	  This adds an extra check when data is written to the flash.
+	  It may help if you are verifying chip setup (timings etc) on
+	  your board.  There is a rare possibility that even though the
+	  device thinks the write was successful, a bit could have been
+	  flipped accidentally due to device wear or something else.
+
+config MTD_DATAFLASH_OTP
+	bool "DataFlash OTP support (Security Register)"
+	depends on MTD_DATAFLASH
+	help
+	  Newer DataFlash chips (revisions C and D) support 128 bytes of
+	  one-time-programmable (OTP) data.  The first half may be written
+	  (once) with up to 64 bytes of data, such as a serial number or
+	  other key product data.  The second half is programmed with a
+	  unique-to-each-chip bit pattern at the factory.
+
+config MTD_MCHP23K256
+	tristate "Microchip 23K256 SRAM"
+	depends on SPI_MASTER
+	help
+	  This enables access to Microchip 23K256 SRAM chips, using SPI.
+
+	  Set up your spi devices with the right board-specific
+	  platform data, or a device tree description if you want to
+	  specify device partitioning
+
+config MTD_MCHP48L640
+	tristate "Microchip 48L640 EERAM"
+	depends on SPI_MASTER
+	help
+	  This enables access to Microchip 48L640 EERAM chips, using SPI.
+
+config MTD_SPEAR_SMI
+	tristate "SPEAR MTD NOR Support through SMI controller"
+	depends on PLAT_SPEAR || COMPILE_TEST
+	default PLAT_SPEAR
+	help
+	  This enable SNOR support on SPEAR platforms using SMI controller
+
+config MTD_SST25L
+	tristate "Support SST25L (non JEDEC) SPI Flash chips"
+	depends on SPI_MASTER
+	help
+	  This enables access to the non JEDEC SST25L SPI flash chips, used
+	  for program and data storage.
+
+	  Set up your spi devices with the right board-specific platform data,
+	  if you want to specify device partitioning.
+
+config MTD_BCM47XXSFLASH
+	tristate "Support for serial flash on BCMA bus"
+	depends on BCMA_SFLASH && (MIPS || ARM)
+	help
+	  BCMA bus can have various flash memories attached, they are
+	  registered by bcma as platform devices. This enables driver for
+	  serial flash memories.
+
+config MTD_SLRAM
+	tristate "Uncached system RAM"
+	help
+	  If your CPU cannot cache all of the physical memory in your machine,
+	  you can still use it for storage or swap by using this driver to
+	  present it to the system as a Memory Technology Device.
+
+config MTD_PHRAM
+	tristate "Physical system RAM"
+	help
+	  This is a re-implementation of the slram driver above.
+
+	  Use this driver to access physical memory that the kernel proper
+	  doesn't have access to, memory beyond the mem=xxx limit, nvram,
+	  memory on the video card, etc...
+
+config MTD_MTDRAM
+	tristate "Test driver using RAM"
+	help
+	  This enables a test MTD device driver which uses vmalloc() to
+	  provide storage.  You probably want to say 'N' unless you're
+	  testing stuff.
+
+config MTDRAM_TOTAL_SIZE
+	int "MTDRAM device size in KiB"
+	depends on MTD_MTDRAM
+	default "4096"
+	help
+	  This allows you to configure the total size of the MTD device
+	  emulated by the MTDRAM driver.  If the MTDRAM driver is built
+	  as a module, it is also possible to specify this as a parameter when
+	  loading the module.
+
+config MTDRAM_ERASE_SIZE
+	int "MTDRAM erase block size in KiB"
+	depends on MTD_MTDRAM
+	default "128"
+	help
+	  This allows you to configure the size of the erase blocks in the
+	  device emulated by the MTDRAM driver.  If the MTDRAM driver is built
+	  as a module, it is also possible to specify this as a parameter when
+	  loading the module.
+
+config MTD_BLOCK2MTD
+	tristate "MTD using block device"
+	depends on BLOCK
+	help
+	  This driver allows a block device to appear as an MTD. It would
+	  generally be used in the following cases:
+
+	  Using Compact Flash as an MTD, these usually present themselves to
+	  the system as an ATA drive.
+	  Testing MTD users (eg JFFS2) on large media and media that might
+	  be removed during a write (using the floppy drive).
+
+config MTD_POWERNV_FLASH
+	tristate "powernv flash MTD driver"
+	depends on PPC_POWERNV
+	help
+	  This provides an MTD device to access flash on powernv OPAL
+	  platforms from Linux. This device abstracts away the
+	  firmware interface for flash access.
+
+config MTD_INTEL_DG
+	tristate "Intel Discrete Graphics non-volatile memory driver"
+	depends on AUXILIARY_BUS && MTD
+	depends on DRM_I915!=n || DRM_XE!=n || COMPILE_TEST
+	help
+	  This provides an MTD device to access Intel Discrete Graphics
+	  non-volatile memory.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called mtd-intel-dg.
+
+comment "Disk-On-Chip Device Drivers"
+
+config MTD_DOCG3
+	tristate "M-Systems Disk-On-Chip G3"
+	select BCH
+	select BCH_CONST_PARAMS if !MTD_NAND_ECC_SW_BCH
+	select BITREVERSE
+	help
+	  This provides an MTD device driver for the M-Systems DiskOnChip
+	  G3 devices.
+
+	  The driver provides access to G3 DiskOnChip, distributed by
+	  M-Systems and now Sandisk. The support is very experimental,
+	  and doesn't give access to any write operations.
+
+config MTD_ST_SPI_FSM
+	tristate "ST Microelectronics SPI FSM Serial Flash Controller"
+	depends on ARCH_STI
+	help
+	  This provides an MTD device driver for the ST Microelectronics
+	  SPI Fast Sequence Mode (FSM) Serial Flash Controller and support
+	  for a subset of connected Serial Flash devices.
+
+if MTD_DOCG3
+config BCH_CONST_M
+	default 14
+config BCH_CONST_T
+	default 4
+endif
+
+endmenu