objtool reports the following warnings for __schedule():
kernel/sched/core.o: warning: objtool:__schedule()+0x3c0: duplicate frame pointer save
kernel/sched/core.o: warning: objtool:__schedule()+0x3fd: sibling call from callable instruction with changed frame pointer
kernel/sched/core.o: warning: objtool:__schedule()+0x40a: call without frame pointer save/setup
kernel/sched/core.o: warning: objtool:__schedule()+0x7fd: frame pointer state mismatch
kernel/sched/core.o: warning: objtool:__schedule()+0x421: frame pointer state mismatch
Basically it's confused by two unusual attributes of the switch_to()
macro:
1. It saves prev's frame pointer to the old stack and restores next's
frame pointer from the new stack.
2. For new tasks it jumps directly to ret_from_fork.
Eventually it would probably be a good idea to clean up the
ret_from_fork hack so that new tasks are created with a valid initial
stack, as suggested by Andy:
https://lkml.kernel.org/r/CALCETrWsqCw4L1qKO9j9L5F+4ED4viuLQTFc=n1pKBZfFPQUFg@mail.gmail.com
Then __schedule() could return normally into the new code and objtool
hopefully wouldn't have a problem anymore.
In the meantime, mark its stack frame as non-standard so we can have a
baseline with no objtool warnings. The marker also serves as a reminder
that this code could be improved a bit.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/91190e324ebd7fcd01748d508d0dfd4693e84d91.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Code which runs outside the kernel's normal mode of operation often does
unusual things which can cause a static analysis tool like objtool to
emit false positive warnings:
- boot image
- vdso image
- relocation
- realmode
- efi
- head
- purgatory
- modpost
Set OBJECT_FILES_NON_STANDARD for their related files and directories,
which will tell objtool to skip checking them. It's ok to skip them
because they don't affect runtime stack traces.
Also skip the following code which does the right thing with respect to
frame pointers, but is too "special" to be validated by a tool:
- entry
- mcount
Also skip the test_nx module because it modifies its exception handling
table at runtime, which objtool can't understand. Fortunately it's
just a test module so it doesn't matter much.
Currently objtool is the only user of OBJECT_FILES_NON_STANDARD, but it
might eventually be useful for other tools.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/366c080e3844e8a5b6a0327dc7e8c2b90ca3baeb.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull ARC fixes from Vineet Gupta:
- Fix for csd deadlock due to missing self IPI
- Accompanying IPI cleanups / optimization
- Brown paper bag bug in one of the cleanups above
- Boot reporting updates for new hardware features
- Don't force DEVTMPFS if INITRAMFS
* tag 'arc-4.5-rc6-fixes-upd' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc:
arc: SMP: CONFIG_ARC_IPI_DBG cleanup
ARC: SMP: No need for CONFIG_ARC_IPI_DBG
ARCv2: Elide sending new cross core intr if receiver didn't ack prev
ARCv2: SMP: Push IPI_IRQ into IPI provider
ARC: [intc-compact] Remove IPI setup from ARCompact port
ARCv2: SMP: Emulate IPI to self using software triggered interrupt
arc: get rid of DEVTMPFS dependency on INITRAMFS_SOURCE
ARCv2: boot report CCMs (Closely Coupled Memories)
ARCv2: boot print Low Latency Memory
ARC: Assume multiplier is always present
Pull vfs fixes from Al Viro:
"Assorted fixes - xattr one from this cycle, the rest - stable fodder"
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
fs/pnode.c: treat zero mnt_group_id-s as unequal
affs_do_readpage_ofs(): just use kmap_atomic() around memcpy()
xattr handlers: plug a lock leak in simple_xattr_list
fs: allow no_seek_end_llseek to actually seek
Previous Commit ("ARC: SMP: No need for CONFIG_ARC_IPI_DBG") removed
the Kconfig option ARC_IPI_DBG. Remove the last reference on this
option.
Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
If __preempt_schedule() or __preempt_schedule_notrace() is referenced at
the beginning of a function, gcc can insert the asm inline "call
___preempt_schedule[_notrace]" instruction before setting up a stack
frame, which breaks frame pointer convention if CONFIG_FRAME_POINTER is
enabled and can result in bad stack traces.
Force a stack frame to be created if CONFIG_FRAME_POINTER is enabled by
listing the stack pointer as an output operand for the inline asm
statements.
Specifically this fixes the following stacktool warnings:
stacktool: drivers/scsi/hpsa.o: hpsa_scsi_do_simple_cmd.constprop.106()+0x79: call without frame pointer save/setup
stacktool: fs/mbcache.o: mb_cache_entry_find_first()+0x70: call without frame pointer save/setup
stacktool: fs/mbcache.o: mb_cache_entry_find_first()+0x92: call without frame pointer save/setup
stacktool: fs/mbcache.o: mb_cache_entry_free()+0xff: call without frame pointer save/setup
stacktool: fs/mbcache.o: mb_cache_entry_free()+0xf5: call without frame pointer save/setup
stacktool: fs/mbcache.o: mb_cache_entry_free()+0x11a: call without frame pointer save/setup
stacktool: fs/mbcache.o: mb_cache_entry_get()+0x225: call without frame pointer save/setup
stacktool: kernel/locking/percpu-rwsem.o: percpu_up_read()+0x27: call without frame pointer save/setup
stacktool: kernel/profile.o: do_profile_hits.isra.5()+0x139: call without frame pointer save/setup
stacktool: lib/nmi_backtrace.o: nmi_trigger_all_cpu_backtrace()+0x2b6: call without frame pointer save/setup
stacktool: net/rds/ib_cm.o: rds_ib_cq_comp_handler_recv()+0x58: call without frame pointer save/setup
stacktool: net/rds/ib_cm.o: rds_ib_cq_comp_handler_send()+0x58: call without frame pointer save/setup
stacktool: net/rds/ib_recv.o: rds_ib_attempt_ack()+0xc1: call without frame pointer save/setup
stacktool: net/rds/iw_recv.o: rds_iw_attempt_ack()+0xc1: call without frame pointer save/setup
stacktool: net/rds/iw_recv.o: rds_iw_recv_cq_comp_handler()+0x55: call without frame pointer save/setup
So it only adds a stack frame to 15 call sites out of ~5000 calls to
___preempt_schedule[_notrace](). All the others already had stack frames.
Oddly, this change actually seems to make things faster in a lot of
cases. For many smaller functions it causes the stack frame creation to
get moved out of the common path and into the unlikely path.
For example, here's the original cyc2ns_read_end():
ffffffff8101f8c0 <cyc2ns_read_end>:
ffffffff8101f8c0: 55 push %rbp
ffffffff8101f8c1: 48 89 e5 mov %rsp,%rbp
ffffffff8101f8c4: 83 6f 10 01 subl $0x1,0x10(%rdi)
ffffffff8101f8c8: 75 08 jne ffffffff8101f8d2 <cyc2ns_read_end+0x12>
ffffffff8101f8ca: 65 48 89 3d e6 5a ff mov %rdi,%gs:0x7eff5ae6(%rip) # 153b8 <cyc2ns+0x38>
ffffffff8101f8d1: 7e
ffffffff8101f8d2: 65 ff 0d 77 c4 fe 7e decl %gs:0x7efec477(%rip) # bd50 <__preempt_count>
ffffffff8101f8d9: 74 02 je ffffffff8101f8dd <cyc2ns_read_end+0x1d>
ffffffff8101f8db: 5d pop %rbp
ffffffff8101f8dc: c3 retq
ffffffff8101f8dd: e8 1e 37 fe ff callq ffffffff81003000 <___preempt_schedule>
ffffffff8101f8e2: 5d pop %rbp
ffffffff8101f8e3: c3 retq
ffffffff8101f8e4: 66 66 66 2e 0f 1f 84 data16 data16 nopw %cs:0x0(%rax,%rax,1)
ffffffff8101f8eb: 00 00 00 00 00
And here's the same function with the patch:
ffffffff8101f8c0 <cyc2ns_read_end>:
ffffffff8101f8c0: 83 6f 10 01 subl $0x1,0x10(%rdi)
ffffffff8101f8c4: 75 08 jne ffffffff8101f8ce <cyc2ns_read_end+0xe>
ffffffff8101f8c6: 65 48 89 3d ea 5a ff mov %rdi,%gs:0x7eff5aea(%rip) # 153b8 <cyc2ns+0x38>
ffffffff8101f8cd: 7e
ffffffff8101f8ce: 65 ff 0d 7b c4 fe 7e decl %gs:0x7efec47b(%rip) # bd50 <__preempt_count>
ffffffff8101f8d5: 74 01 je ffffffff8101f8d8 <cyc2ns_read_end+0x18>
ffffffff8101f8d7: c3 retq
ffffffff8101f8d8: 55 push %rbp
ffffffff8101f8d9: 48 89 e5 mov %rsp,%rbp
ffffffff8101f8dc: e8 1f 37 fe ff callq ffffffff81003000 <___preempt_schedule>
ffffffff8101f8e1: 5d pop %rbp
ffffffff8101f8e2: c3 retq
ffffffff8101f8e3: 66 66 66 66 2e 0f 1f data16 data16 data16 nopw %cs:0x0(%rax,%rax,1)
ffffffff8101f8ea: 84 00 00 00 00 00
Notice that it moved the frame pointer setup code to the unlikely
___preempt_schedule() call path. Going through a sampling of the
differences in the asm, that's the most common change I see.
Otherwise it has no real effect on callers which already have stack
frames (though it does result in the reordering of some 'mov's).
Reported-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: 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: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/20160218174158.GA28230@treble.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
