So the dwarf2 annotations in low level assembly code have
become an increasing hindrance: unreadable, messy macros
mixed into some of the most security sensitive code paths
of the Linux kernel.
These debug info annotations don't even buy the upstream
kernel anything: dwarf driven stack unwinding has caused
problems in the past so it's out of tree, and the upstream
kernel only uses the much more robust framepointers based
stack unwinding method.
In addition to that there's a steady, slow bitrot going
on with these annotations, requiring frequent fixups.
There's no tooling and no functionality upstream that
keeps it correct.
So burn down the sick forest, allowing new, healthier growth:
27 files changed, 350 insertions(+), 1101 deletions(-)
Someone who has the willingness and time to do this
properly can attempt to reintroduce dwarf debuginfo in x86
assembly code plus dwarf unwinding from first principles,
with the following conditions:
- it should be maximally readable, and maximally low-key to
'ordinary' code reading and maintenance.
- find a build time method to insert dwarf annotations
automatically in the most common cases, for pop/push
instructions that manipulate the stack pointer. This could
be done for example via a preprocessing step that just
looks for common patterns - plus special annotations for
the few cases where we want to depart from the default.
We have hundreds of CFI annotations, so automating most of
that makes sense.
- it should come with build tooling checks that ensure that
CFI annotations are sensible. We've seen such efforts from
the framepointer side, and there's no reason it couldn't be
done on the dwarf side.
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The early_idt_handlers asm code generates an array of entry
points spaced nine bytes apart. It's not really clear from that
code or from the places that reference it what's going on, and
the code only works in the first place because GAS never
generates two-byte JMP instructions when jumping to global
labels.
Clean up the code to generate the correct array stride (member size)
explicitly. This should be considerably more robust against
screw-ups, as GAS will warn if a .fill directive has a negative
count. Using '. =' to advance would have been even more robust
(it would generate an actual error if it tried to move
backwards), but it would pad with nulls, confusing anyone who
tries to disassemble the code. The new scheme should be much
clearer to future readers.
While we're at it, improve the comments and rename the array and
common code.
Binutils may start relaxing jumps to non-weak labels. If so,
this change will fix our build, and we may need to backport this
change.
Before, on x86_64:
0000000000000000 <early_idt_handlers>:
0: 6a 00 pushq $0x0
2: 6a 00 pushq $0x0
4: e9 00 00 00 00 jmpq 9 <early_idt_handlers+0x9>
5: R_X86_64_PC32 early_idt_handler-0x4
...
48: 66 90 xchg %ax,%ax
4a: 6a 08 pushq $0x8
4c: e9 00 00 00 00 jmpq 51 <early_idt_handlers+0x51>
4d: R_X86_64_PC32 early_idt_handler-0x4
...
117: 6a 00 pushq $0x0
119: 6a 1f pushq $0x1f
11b: e9 00 00 00 00 jmpq 120 <early_idt_handler>
11c: R_X86_64_PC32 early_idt_handler-0x4
After:
0000000000000000 <early_idt_handler_array>:
0: 6a 00 pushq $0x0
2: 6a 00 pushq $0x0
4: e9 14 01 00 00 jmpq 11d <early_idt_handler_common>
...
48: 6a 08 pushq $0x8
4a: e9 d1 00 00 00 jmpq 120 <early_idt_handler_common>
4f: cc int3
50: cc int3
...
117: 6a 00 pushq $0x0
119: 6a 1f pushq $0x1f
11b: eb 03 jmp 120 <early_idt_handler_common>
11d: cc int3
11e: cc int3
11f: cc int3
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Binutils <binutils@sourceware.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H.J. Lu <hjl.tools@gmail.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ac027962af343b0c599cbfcf50b945ad2ef3d7a8.1432336324.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Packing loops tightly (-falign-loops=1) is beneficial to code size:
text data bss dec filename
12566391 1617840 1089536 15273767 vmlinux.align.16-byte
12224951 1617840 1089536 14932327 vmlinux.align.1-byte
11976567 1617840 1089536 14683943 vmlinux.align.1-byte.funcs-1-byte
11903735 1617840 1089536 14611111 vmlinux.align.1-byte.funcs-1-byte.loops-1-byte
Which reduces the size of the kernel by another 0.6%, so the
the total combined size reduction of the alignment-packing
patches is ~5.5%.
The x86 decoder bandwidth and caching arguments laid out in:
be6cb02779 ("x86: Align jump targets to 1-byte boundaries")
apply to loop alignment as well.
Furtermore, modern CPU uarchs have a loop cache/buffer that
is a L0 cache before even any uop cache, covering a few
dozen most recently executed instructions.
This loop cache generally does not have the 16-byte alignment
restrictions of the uop cache.
Now loop alignment can still be beneficial if:
- a loop is cache-hot and its surroundings are not.
- if the loop is so cache hot that the instruction
flow becomes x86 decoder bandwidth limited
But loop alignment is harmful if:
- a loop is cache-cold
- a loop's surroundings are cache-hot as well
- two cache-hot loops are close to each other
- if the loop fits into the loop cache
- if the code flow is not decoder bandwidth limited
and I'd argue that the latter five scenarios are much
more common in the kernel, as our hottest loops are
typically:
- pointer chasing: this should fit into the loop cache
in most cases and is typically data cache and address
generation limited
- generic memory ops (memset, memcpy, etc.): these generally
fit into the loop cache as well, and are likewise data
cache limited.
So this patch packs loop addresses tightly as well.
Acked-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20150410123017.GB19918@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull USB fixes from Greg KH:
"Here are some USB fixes and new device ids for 4.1-rc4.
All are pretty minor, and have been in linux-next successfully"
* tag 'usb-4.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb:
usb-storage: Add NO_WP_DETECT quirk for Lacie 059f:0651 devices
Added another USB product ID for ELAN touchscreen quirks.
xhci: gracefully handle xhci_irq dead device
xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256
xhci: fix isoc endpoint dequeue from advancing too far on transaction error
usb: chipidea: debug: avoid out of bound read
USB: visor: Match I330 phone more precisely
USB: pl2303: Remove support for Samsung I330
USB: cp210x: add ID for KCF Technologies PRN device
usb: gadget: remove incorrect __init/__exit annotations
usb: phy: isp1301: work around tps65010 dependency
usb: gadget: serial: fix re-ordering of tx data
usb: gadget: hid: Fix static variable usage
usb: gadget: configfs: Fix interfaces array NULL-termination
usb: gadget: xilinx: fix devm_ioremap_resource() check
usb: dwc3: dwc3-omap: correct the register macros
Pull tty/serial fixes from Greg KH:
"Here's some TTY and serial driver fixes for reported issues.
All of these have been in linux-next successfully"
* tag 'tty-4.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
pty: Fix input race when closing
tty/n_gsm.c: fix a memory leak when gsmtty is removed
Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is not open"
serial: omap: Fix error handling in probe
earlycon: Revert log warnings
Pull staging / IIO driver fixes from Greg KH:
"Here's some staging and iio driver fixes to resolve a number of
reported issues.
All of these have been in linux-next for a while"
* tag 'staging-4.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging: (31 commits)
iio: light: hid-sensor-prox: Fix memory leak in probe()
iio: adc: cc10001: Add delay before setting START bit
iio: adc: cc10001: Fix regulator_get_voltage() return value check
iio: adc: cc10001: Fix incorrect use of power-up/power-down register
staging: gdm724x: Correction of variable usage after applying ALIGN()
iio: adc: cc10001: Fix the channel number mapping
staging: vt6655: lock MACvWriteBSSIDAddress.
staging: vt6655: CARDbUpdateTSF bss timestamp correct tsf counter value.
staging: vt6655: vnt_tx_packet Correct TX order of OWNED_BY_NIC
staging: vt6655: Fix 80211 control and management status reporting.
staging: vt6655: implement IEEE80211_TX_STAT_NOACK_TRANSMITTED
staging: vt6655: device_free_tx_buf use only ieee80211_tx_status_irqsafe
staging: vt6656: use ieee80211_tx_info to select packet type.
staging: rtl8712: freeing an ERR_PTR
staging: sm750: remove incorrect __exit annotation
iio: kfifo: Set update_needed to false only if a buffer was allocated
iio: mcp320x: Fix occasional incorrect readings
iio: accel: mma9553: check input value for activity period
iio: accel: mma9553: add enable channel for activity
iio: accel: mma9551_core: prevent buffer overrun
...
Pull char/misc fix from Greg KH:
"Here is one fix, in the extcon subsystem, that resolves a reported
issue.
It's been in linux-next for a number of weeks now, sorry for not
getting it to you sooner"
* tag 'char-misc-4.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
extcon: usb-gpio: register extcon device before IRQ registration
Pull UML hostfs fix from Richard Weinberger:
"This contains a single fix for a regression introduced in 4.1-rc1"
* 'for-linus-4.1-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml:
hostfs: Use correct mask for file mode
Pull UBI bufix from Richard Weinberger:
"This contains a single bug fix for the UBI block driver"
* tag 'upstream-4.1-rc4' of git://git.infradead.org/linux-ubifs:
UBI: block: Add missing cache flushes
Pull ext4 fixes from Ted Ts'o:
"Fix a number of ext4 bugs; the most serious of which is a bug in the
lazytime mount optimization code where we could end up updating the
timestamps to the wrong inode"
* tag 'for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
ext4: fix an ext3 collapse range regression in xfstests
jbd2: fix r_count overflows leading to buffer overflow in journal recovery
ext4: check for zero length extent explicitly
ext4: fix NULL pointer dereference when journal restart fails
ext4: remove unused function prototype from ext4.h
ext4: don't save the error information if the block device is read-only
ext4: fix lazytime optimization
Pull btrfs fixes from Chris Mason:
"The first commit is a fix from Filipe for a very old extent buffer
reuse race that triggered a BUG_ON. It hasn't come up often, I looked
through old logs at FB and we hit it a handful of times over the last
year.
The rest are other corners he hit during testing"
* 'for-linus-4.1' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs:
Btrfs: fix race when reusing stale extent buffers that leads to BUG_ON
Btrfs: fix race between block group creation and their cache writeout
Btrfs: fix panic when starting bg cache writeout after IO error
Btrfs: fix crash after inode cache writeback failure
Pull MIPS fixes from Ralf Baechle:
"Seven small fixes. The shortlog below is a good description so no
need to elaborate.
It has sat in linux-next and survived the usual automated testing by
Imagination's test farm"
* 'master' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus:
MIPS: tlb-r4k: Fix PG_ELPA comment
MIPS: Fix up obsolete cpu_set usage
MIPS: IP32: Fix build errors in reset code in DS1685 platform hook.
MIPS: KVM: Fix unused variable build warning
MIPS: traps: remove extra Tainted: line from __show_regs() output
MIPS: Fix wrong CHECKFLAGS (sparse builds) with GCC 5.1
MIPS: Fix a preemption issue with thread's FPU defaults
Pull ARM SoC fixes from Arnd Bergmann:
"Nothing frightening this time, just smaller fixes in a number of
places.
The other changes contained here are:
MAINTAINERS file updates:
- The mach-gemini maintainer is back in action and has a new git tree
- Krzysztof Kozlowski has volunteered to be a new co-maintainer for
the samsung platforms
- updates to the files that belong to Marvell mvebu
Bug fixes:
- The largest changes are on omap2, but are only to avoid some
harmless warnings and to fix reset on omap4
- a small regression fix on tegra
- multiple fixes for incorrect IRQ affinity on vexpress
- the missing system controller on arm64 juno is added
- one revert of a patch that was accidentally applied twice for
mach-rockchip
- two clock related DT fixes for mvebu
- a workaround for suspend with old DT binaries on new exynos kernels
- Another fix for suspend on exynos, needs to be backported"
* tag 'fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc: (21 commits)
MAINTAINERS: Add dts entries for some of the Marvell SoCs
MAINTAINERS: ARM: EXYNOS: Add Krzysztof Kozlowski as co-maintainer
ARM: EXYNOS: Use of_machine_is_compatible instead of soc_is_exynos4
ARM: EXYNOS: Fix failed second suspend on Exynos4
Revert "ARM: rockchip: fix undefined instruction of reset_ctrl_regs"
ARM: EXYNOS: Fix dereference of ERR_PTR returned by of_genpd_get_from_provider
ARM: EXYNOS: Don't try to initialize suspend on old DT
ARM: dts: Add keep-power-in-suspend to WiFi SDIO node for Peach Boards
ARM: gemini: fix compiler warning due wrong data type
ARM: vexpress/tc2: Add interrupt-affinity to the PMU node
ARM: vexpress/ca9: Add interrupt-affinity to the PMU node
ARM: vexpress/ca9: Add unified-cache property to l2 cache node
ARM64: juno: add sp810 support and fix sp804 clock frequency
ARM: Gemini: Maintainers update
ARM: OMAP2+: Remove bogus struct clk comparison for timer clock
ARM: dove: Add clock-names to CuBox Si5351 clk generator
ARM: AM33xx+: hwmod: re-use omap4 implementations for reset functionality
ARM: OMAP4+: PRM: add support for passing status register/bit info to reset
ARM: AM43xx: hwmod: add VPFE hwmod entries
ARM: mvebu: Fix the main PLL frequency on Armada 375, 38x and 39x SoCs
...
Ingo Molnar
Jan Beulich
Andy Lutomirski
Denys Vlasenko
Borislav Petkov
Linus Torvalds