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, 547 insertions, 0 deletions

diff --git a/Documentation/userspace-api/ioctl/hdio.rst b/Documentation/userspace-api/ioctl/hdio.rst
new file mode 100644
index 000000000..6ee8fc886
--- /dev/null
+++ b/Documentation/userspace-api/ioctl/hdio.rst
@@ -0,0 +1,547 @@
+==============================
+Summary of `HDIO_` ioctl calls
+==============================
+
+- Edward A. Falk <efalk@google.com>
+
+November, 2004
+
+This document attempts to describe the ioctl(2) calls supported by
+the HD/IDE layer.  These are by-and-large implemented (as of Linux 5.11)
+drivers/ata/libata-scsi.c.
+
+ioctl values are listed in <linux/hdreg.h>.  As of this writing, they
+are as follows:
+
+    ioctls that pass argument pointers to user space:
+
+	=======================	=======================================
+	HDIO_GETGEO		get device geometry
+	HDIO_GET_32BIT		get current io_32bit setting
+	HDIO_GET_IDENTITY	get IDE identification info
+	HDIO_DRIVE_TASKFILE	execute raw taskfile
+	HDIO_DRIVE_TASK		execute task and special drive command
+	HDIO_DRIVE_CMD		execute a special drive command
+	=======================	=======================================
+
+    ioctls that pass non-pointer values:
+
+	=======================	=======================================
+	HDIO_SET_32BIT		change io_32bit flags
+	=======================	=======================================
+
+
+The information that follows was determined from reading kernel source
+code.  It is likely that some corrections will be made over time.
+
+------------------------------------------------------------------------------
+
+General:
+
+	Unless otherwise specified, all ioctl calls return 0 on success
+	and -1 with errno set to an appropriate value on error.
+
+	Unless otherwise specified, all ioctl calls return -1 and set
+	errno to EFAULT on a failed attempt to copy data to or from user
+	address space.
+
+	Unless otherwise specified, all data structures and constants
+	are defined in <linux/hdreg.h>
+
+------------------------------------------------------------------------------
+
+HDIO_GETGEO
+	get device geometry
+
+
+	usage::
+
+	  struct hd_geometry geom;
+
+	  ioctl(fd, HDIO_GETGEO, &geom);
+
+
+	inputs:
+		none
+
+
+
+	outputs:
+		hd_geometry structure containing:
+
+
+	    =========	==================================
+	    heads	number of heads
+	    sectors	number of sectors/track
+	    cylinders	number of cylinders, mod 65536
+	    start	starting sector of this partition.
+	    =========	==================================
+
+
+	error returns:
+	  - EINVAL
+
+			if the device is not a disk drive or floppy drive,
+			or if the user passes a null pointer
+
+
+	notes:
+		Not particularly useful with modern disk drives, whose geometry
+		is a polite fiction anyway.  Modern drives are addressed
+		purely by sector number nowadays (lba addressing), and the
+		drive geometry is an abstraction which is actually subject
+		to change.  Currently (as of Nov 2004), the geometry values
+		are the "bios" values -- presumably the values the drive had
+		when Linux first booted.
+
+		In addition, the cylinders field of the hd_geometry is an
+		unsigned short, meaning that on most architectures, this
+		ioctl will not return a meaningful value on drives with more
+		than 65535 tracks.
+
+		The start field is unsigned long, meaning that it will not
+		contain a meaningful value for disks over 219 Gb in size.
+
+
+
+HDIO_GET_IDENTITY
+	get IDE identification info
+
+
+	usage::
+
+	  unsigned char identity[512];
+
+	  ioctl(fd, HDIO_GET_IDENTITY, identity);
+
+	inputs:
+		none
+
+
+
+	outputs:
+		ATA drive identity information.  For full description, see
+		the IDENTIFY DEVICE and IDENTIFY PACKET DEVICE commands in
+		the ATA specification.
+
+	error returns:
+	  - EINVAL	Called on a partition instead of the whole disk device
+	  - ENOMSG	IDENTIFY DEVICE information not available
+
+	notes:
+		Returns information that was obtained when the drive was
+		probed.  Some of this information is subject to change, and
+		this ioctl does not re-probe the drive to update the
+		information.
+
+		This information is also available from /proc/ide/hdX/identify
+
+
+
+HDIO_GET_32BIT
+	get current io_32bit setting
+
+
+	usage::
+
+	  long val;
+
+	  ioctl(fd, HDIO_GET_32BIT, &val);
+
+	inputs:
+		none
+
+
+
+	outputs:
+		The value of the current io_32bit setting
+
+
+
+	notes:
+		0=16-bit, 1=32-bit, 2,3 = 32bit+sync
+
+
+
+HDIO_DRIVE_TASKFILE
+	execute raw taskfile
+
+
+	Note:
+		If you don't have a copy of the ANSI ATA specification
+		handy, you should probably ignore this ioctl.
+
+	- Execute an ATA disk command directly by writing the "taskfile"
+	  registers of the drive.  Requires ADMIN and RAWIO access
+	  privileges.
+
+	usage::
+
+	  struct {
+
+	    ide_task_request_t req_task;
+	    u8 outbuf[OUTPUT_SIZE];
+	    u8 inbuf[INPUT_SIZE];
+	  } task;
+	  memset(&task.req_task, 0, sizeof(task.req_task));
+	  task.req_task.out_size = sizeof(task.outbuf);
+	  task.req_task.in_size = sizeof(task.inbuf);
+	  ...
+	  ioctl(fd, HDIO_DRIVE_TASKFILE, &task);
+	  ...
+
+	inputs:
+
+	  (See below for details on memory area passed to ioctl.)
+
+	  ============	===================================================
+	  io_ports[8]	values to be written to taskfile registers
+	  hob_ports[8]	high-order bytes, for extended commands.
+	  out_flags	flags indicating which registers are valid
+	  in_flags	flags indicating which registers should be returned
+	  data_phase	see below
+	  req_cmd	command type to be executed
+	  out_size	size of output buffer
+	  outbuf	buffer of data to be transmitted to disk
+	  inbuf		buffer of data to be received from disk (see [1])
+	  ============	===================================================
+
+	outputs:
+
+	  ===========	====================================================
+	  io_ports[]	values returned in the taskfile registers
+	  hob_ports[]	high-order bytes, for extended commands.
+	  out_flags	flags indicating which registers are valid (see [2])
+	  in_flags	flags indicating which registers should be returned
+	  outbuf	buffer of data to be transmitted to disk (see [1])
+	  inbuf		buffer of data to be received from disk
+	  ===========	====================================================
+
+	error returns:
+	  - EACCES	CAP_SYS_ADMIN or CAP_SYS_RAWIO privilege not set.
+	  - ENOMSG	Device is not a disk drive.
+	  - ENOMEM	Unable to allocate memory for task
+	  - EFAULT	req_cmd == TASKFILE_IN_OUT (not implemented as of 2.6.8)
+	  - EPERM
+
+			req_cmd == TASKFILE_MULTI_OUT and drive
+			multi-count not yet set.
+	  - EIO		Drive failed the command.
+
+	notes:
+
+	  [1] READ THE FOLLOWING NOTES *CAREFULLY*.  THIS IOCTL IS
+	  FULL OF GOTCHAS.  Extreme caution should be used with using
+	  this ioctl.  A mistake can easily corrupt data or hang the
+	  system.
+
+	  [2] Both the input and output buffers are copied from the
+	  user and written back to the user, even when not used.
+
+	  [3] If one or more bits are set in out_flags and in_flags is
+	  zero, the following values are used for in_flags.all and
+	  written back into in_flags on completion.
+
+	   * IDE_TASKFILE_STD_IN_FLAGS | (IDE_HOB_STD_IN_FLAGS << 8)
+	     if LBA48 addressing is enabled for the drive
+	   * IDE_TASKFILE_STD_IN_FLAGS
+	     if CHS/LBA28
+
+	  The association between in_flags.all and each enable
+	  bitfield flips depending on endianness; fortunately, TASKFILE
+	  only uses inflags.b.data bit and ignores all other bits.
+	  The end result is that, on any endian machines, it has no
+	  effect other than modifying in_flags on completion.
+
+	  [4] The default value of SELECT is (0xa0|DEV_bit|LBA_bit)
+	  except for four drives per port chipsets.  For four drives
+	  per port chipsets, it's (0xa0|DEV_bit|LBA_bit) for the first
+	  pair and (0x80|DEV_bit|LBA_bit) for the second pair.
+
+	  [5] The argument to the ioctl is a pointer to a region of
+	  memory containing a ide_task_request_t structure, followed
+	  by an optional buffer of data to be transmitted to the
+	  drive, followed by an optional buffer to receive data from
+	  the drive.
+
+	  Command is passed to the disk drive via the ide_task_request_t
+	  structure, which contains these fields:
+
+	    ============	===============================================
+	    io_ports[8]		values for the taskfile registers
+	    hob_ports[8]	high-order bytes, for extended commands
+	    out_flags		flags indicating which entries in the
+				io_ports[] and hob_ports[] arrays
+				contain valid values.  Type ide_reg_valid_t.
+	    in_flags		flags indicating which entries in the
+				io_ports[] and hob_ports[] arrays
+				are expected to contain valid values
+				on return.
+	    data_phase		See below
+	    req_cmd		Command type, see below
+	    out_size		output (user->drive) buffer size, bytes
+	    in_size		input (drive->user) buffer size, bytes
+	    ============	===============================================
+
+	  When out_flags is zero, the following registers are loaded.
+
+	    ============	===============================================
+	    HOB_FEATURE		If the drive supports LBA48
+	    HOB_NSECTOR		If the drive supports LBA48
+	    HOB_SECTOR		If the drive supports LBA48
+	    HOB_LCYL		If the drive supports LBA48
+	    HOB_HCYL		If the drive supports LBA48
+	    FEATURE
+	    NSECTOR
+	    SECTOR
+	    LCYL
+	    HCYL
+	    SELECT		First, masked with 0xE0 if LBA48, 0xEF
+				otherwise; then, or'ed with the default
+				value of SELECT.
+	    ============	===============================================
+
+	  If any bit in out_flags is set, the following registers are loaded.
+
+	    ============	===============================================
+	    HOB_DATA		If out_flags.b.data is set.  HOB_DATA will
+				travel on DD8-DD15 on little endian machines
+				and on DD0-DD7 on big endian machines.
+	    DATA		If out_flags.b.data is set.  DATA will
+				travel on DD0-DD7 on little endian machines
+				and on DD8-DD15 on big endian machines.
+	    HOB_NSECTOR		If out_flags.b.nsector_hob is set
+	    HOB_SECTOR		If out_flags.b.sector_hob is set
+	    HOB_LCYL		If out_flags.b.lcyl_hob is set
+	    HOB_HCYL		If out_flags.b.hcyl_hob is set
+	    FEATURE		If out_flags.b.feature is set
+	    NSECTOR		If out_flags.b.nsector is set
+	    SECTOR		If out_flags.b.sector is set
+	    LCYL		If out_flags.b.lcyl is set
+	    HCYL		If out_flags.b.hcyl is set
+	    SELECT		Or'ed with the default value of SELECT and
+				loaded regardless of out_flags.b.select.
+	    ============	===============================================
+
+	  Taskfile registers are read back from the drive into
+	  {io|hob}_ports[] after the command completes iff one of the
+	  following conditions is met; otherwise, the original values
+	  will be written back, unchanged.
+
+	    1. The drive fails the command (EIO).
+	    2. One or more than one bits are set in out_flags.
+	    3. The requested data_phase is TASKFILE_NO_DATA.
+
+	    ============	===============================================
+	    HOB_DATA		If in_flags.b.data is set.  It will contain
+				DD8-DD15 on little endian machines and
+				DD0-DD7 on big endian machines.
+	    DATA		If in_flags.b.data is set.  It will contain
+				DD0-DD7 on little endian machines and
+				DD8-DD15 on big endian machines.
+	    HOB_FEATURE		If the drive supports LBA48
+	    HOB_NSECTOR		If the drive supports LBA48
+	    HOB_SECTOR		If the drive supports LBA48
+	    HOB_LCYL		If the drive supports LBA48
+	    HOB_HCYL		If the drive supports LBA48
+	    NSECTOR
+	    SECTOR
+	    LCYL
+	    HCYL
+	    ============	===============================================
+
+	  The data_phase field describes the data transfer to be
+	  performed.  Value is one of:
+
+	    ===================        ========================================
+	    TASKFILE_IN
+	    TASKFILE_MULTI_IN
+	    TASKFILE_OUT
+	    TASKFILE_MULTI_OUT
+	    TASKFILE_IN_OUT
+	    TASKFILE_IN_DMA
+	    TASKFILE_IN_DMAQ		== IN_DMA (queueing not supported)
+	    TASKFILE_OUT_DMA
+	    TASKFILE_OUT_DMAQ		== OUT_DMA (queueing not supported)
+	    TASKFILE_P_IN		unimplemented
+	    TASKFILE_P_IN_DMA		unimplemented
+	    TASKFILE_P_IN_DMAQ		unimplemented
+	    TASKFILE_P_OUT		unimplemented
+	    TASKFILE_P_OUT_DMA		unimplemented
+	    TASKFILE_P_OUT_DMAQ		unimplemented
+	    ===================        ========================================
+
+	  The req_cmd field classifies the command type.  It may be
+	  one of:
+
+	    ========================    =======================================
+	    IDE_DRIVE_TASK_NO_DATA
+	    IDE_DRIVE_TASK_SET_XFER	unimplemented
+	    IDE_DRIVE_TASK_IN
+	    IDE_DRIVE_TASK_OUT		unimplemented
+	    IDE_DRIVE_TASK_RAW_WRITE
+	    ========================    =======================================
+
+	  [6] Do not access {in|out}_flags->all except for resetting
+	  all the bits.  Always access individual bit fields.  ->all
+	  value will flip depending on endianness.  For the same
+	  reason, do not use IDE_{TASKFILE|HOB}_STD_{OUT|IN}_FLAGS
+	  constants defined in hdreg.h.
+
+
+
+HDIO_DRIVE_CMD
+	execute a special drive command
+
+
+	Note:  If you don't have a copy of the ANSI ATA specification
+	handy, you should probably ignore this ioctl.
+
+	usage::
+
+	  u8 args[4+XFER_SIZE];
+
+	  ...
+	  ioctl(fd, HDIO_DRIVE_CMD, args);
+
+	inputs:
+	    Commands other than WIN_SMART:
+
+	    =======     =======
+	    args[0]	COMMAND
+	    args[1]	NSECTOR
+	    args[2]	FEATURE
+	    args[3]	NSECTOR
+	    =======     =======
+
+	    WIN_SMART:
+
+	    =======     =======
+	    args[0]	COMMAND
+	    args[1]	SECTOR
+	    args[2]	FEATURE
+	    args[3]	NSECTOR
+	    =======     =======
+
+	outputs:
+		args[] buffer is filled with register values followed by any
+
+
+	  data returned by the disk.
+
+	    ========	====================================================
+	    args[0]	status
+	    args[1]	error
+	    args[2]	NSECTOR
+	    args[3]	undefined
+	    args[4+]	NSECTOR * 512 bytes of data returned by the command.
+	    ========	====================================================
+
+	error returns:
+	  - EACCES	Access denied:  requires CAP_SYS_RAWIO
+	  - ENOMEM	Unable to allocate memory for task
+	  - EIO		Drive reports error
+
+	notes:
+
+	  [1] For commands other than WIN_SMART, args[1] should equal
+	  args[3].  SECTOR, LCYL and HCYL are undefined.  For
+	  WIN_SMART, 0x4f and 0xc2 are loaded into LCYL and HCYL
+	  respectively.  In both cases SELECT will contain the default
+	  value for the drive.  Please refer to HDIO_DRIVE_TASKFILE
+	  notes for the default value of SELECT.
+
+	  [2] If NSECTOR value is greater than zero and the drive sets
+	  DRQ when interrupting for the command, NSECTOR * 512 bytes
+	  are read from the device into the area following NSECTOR.
+	  In the above example, the area would be
+	  args[4..4+XFER_SIZE].  16bit PIO is used regardless of
+	  HDIO_SET_32BIT setting.
+
+	  [3] If COMMAND == WIN_SETFEATURES && FEATURE == SETFEATURES_XFER
+	  && NSECTOR >= XFER_SW_DMA_0 && the drive supports any DMA
+	  mode, IDE driver will try to tune the transfer mode of the
+	  drive accordingly.
+
+
+
+HDIO_DRIVE_TASK
+	execute task and special drive command
+
+
+	Note:  If you don't have a copy of the ANSI ATA specification
+	handy, you should probably ignore this ioctl.
+
+	usage::
+
+	  u8 args[7];
+
+	  ...
+	  ioctl(fd, HDIO_DRIVE_TASK, args);
+
+	inputs:
+	    Taskfile register values:
+
+	    =======	=======
+	    args[0]	COMMAND
+	    args[1]	FEATURE
+	    args[2]	NSECTOR
+	    args[3]	SECTOR
+	    args[4]	LCYL
+	    args[5]	HCYL
+	    args[6]	SELECT
+	    =======	=======
+
+	outputs:
+	    Taskfile register values:
+
+
+	    =======	=======
+	    args[0]	status
+	    args[1]	error
+	    args[2]	NSECTOR
+	    args[3]	SECTOR
+	    args[4]	LCYL
+	    args[5]	HCYL
+	    args[6]	SELECT
+	    =======	=======
+
+	error returns:
+	  - EACCES	Access denied:  requires CAP_SYS_RAWIO
+	  - ENOMEM	Unable to allocate memory for task
+	  - ENOMSG	Device is not a disk drive.
+	  - EIO		Drive failed the command.
+
+	notes:
+
+	  [1] DEV bit (0x10) of SELECT register is ignored and the
+	  appropriate value for the drive is used.  All other bits
+	  are used unaltered.
+
+
+
+HDIO_SET_32BIT
+	change io_32bit flags
+
+
+	usage::
+
+	  int val;
+
+	  ioctl(fd, HDIO_SET_32BIT, val);
+
+	inputs:
+		New value for io_32bit flag
+
+
+
+	outputs:
+		none
+
+
+
+	error return:
+	  - EINVAL	Called on a partition instead of the whole disk device
+	  - EACCES	Access denied:  requires CAP_SYS_ADMIN
+	  - EINVAL	value out of range [0 3]
+	  - EBUSY	Controller busy