linux/tools
Josh Poimboeuf f5caf621ee x86/asm: Fix inline asm call constraints for Clang
For inline asm statements which have a CALL instruction, we list the
stack pointer as a constraint to convince GCC to ensure the frame
pointer is set up first:

  static inline void foo()
  {
	register void *__sp asm(_ASM_SP);
	asm("call bar" : "+r" (__sp))
  }

Unfortunately, that pattern causes Clang to corrupt the stack pointer.

The fix is easy: convert the stack pointer register variable to a global
variable.

It should be noted that the end result is different based on the GCC
version.  With GCC 6.4, this patch has exactly the same result as
before:

	defconfig	defconfig-nofp	distro		distro-nofp
 before	9820389		9491555		8816046		8516940
 after	9820389		9491555		8816046		8516940

With GCC 7.2, however, GCC's behavior has changed.  It now changes its
behavior based on the conversion of the register variable to a global.
That somehow convinces it to *always* set up the frame pointer before
inserting *any* inline asm.  (Therefore, listing the variable as an
output constraint is a no-op and is no longer necessary.)  It's a bit
overkill, but the performance impact should be negligible.  And in fact,
there's a nice improvement with frame pointers disabled:

	defconfig	defconfig-nofp	distro		distro-nofp
 before	9796316		9468236		9076191		8790305
 after	9796957		9464267		9076381		8785949

So in summary, while listing the stack pointer as an output constraint
is no longer necessary for newer versions of GCC, it's still needed for
older versions.

Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3db862e970c432ae823cf515c52b54fec8270e0e.1505942196.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-23 15:06:20 +02:00
..
accounting
arch Merge branch 'parisc-4.14-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux 2017-09-05 09:37:11 -07:00
build tools build tests: Don't hardcode gcc name 2017-08-28 16:44:44 -03:00
cgroup
firewire
gpio gpio-hammer: fix make consumer_label suitable to work on gpio-nails 2017-01-26 16:29:09 +01:00
hv Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2017-09-06 14:45:08 -07:00
iio iio: tools: add install section 2017-08-09 14:31:58 +01:00
include perf/urgent fixes: 2017-09-13 09:25:10 +02:00
kvm/kvm_stat tools/kvm_stat: add '-f help' to get the available event list 2017-07-26 19:04:53 +02:00
laptop
leds tools/leds: Add led_hw_brightness_mon program 2017-02-14 22:20:23 +01:00
lib perf/urgent fixes: 2017-09-13 09:25:10 +02:00
net tools: bpf_jit_disasm: Handle large images. 2017-06-14 15:03:22 -04:00
nfsd
objtool x86/asm: Fix inline asm call constraints for Clang 2017-09-23 15:06:20 +02:00
pci tools: PCI: Add a missing option help line 2017-08-29 16:03:34 -05:00
pcmcia
perf mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
power Kbuild updates for v4.14 2017-09-14 13:46:33 -07:00
scripts Kbuild updates for v4.14 2017-09-14 13:46:33 -07:00
spi spi: tools: add install section 2017-07-26 12:25:28 +01:00
testing Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-09-16 11:28:59 -07:00
thermal/tmon
time
usb usbip: auto retry for concurrent attach 2017-08-31 18:08:45 +02:00
virtio tools/virtio: fix spelling mistake: "wakeus" -> "wakeups" 2017-05-09 16:43:24 +03:00
vm tools/vm: add missing Makefile rules 2017-02-22 16:41:26 -08:00
Makefile spi: Updates for v4.14 2017-09-05 11:40:38 -07:00