linux/kernel
Steven Rostedt 8da3821ba5 ftrace: create __mcount_loc section
This patch creates a section in the kernel called "__mcount_loc".
This will hold a list of pointers to the mcount relocation for
each call site of mcount.

For example:

objdump -dr init/main.o
[...]
Disassembly of section .text:

0000000000000000 <do_one_initcall>:
   0:   55                      push   %rbp
[...]
000000000000017b <init_post>:
 17b:   55                      push   %rbp
 17c:   48 89 e5                mov    %rsp,%rbp
 17f:   53                      push   %rbx
 180:   48 83 ec 08             sub    $0x8,%rsp
 184:   e8 00 00 00 00          callq  189 <init_post+0xe>
                        185: R_X86_64_PC32      mcount+0xfffffffffffffffc
[...]

We will add a section to point to each function call.

   .section __mcount_loc,"a",@progbits
[...]
   .quad .text + 0x185
[...]

The offset to of the mcount call site in init_post is an offset from
the start of the section, and not the start of the function init_post.
The mcount relocation is at the call site 0x185 from the start of the
.text section.

  .text + 0x185  == init_post + 0xa

We need a way to add this __mcount_loc section in a way that we do not
lose the relocations after final link.  The .text section here will
be attached to all other .text sections after final link and the
offsets will be meaningless.  We need to keep track of where these
.text sections are.

To do this, we use the start of the first function in the section.
do_one_initcall.  We can make a tmp.s file with this function as a reference
to the start of the .text section.

   .section __mcount_loc,"a",@progbits
[...]
   .quad do_one_initcall + 0x185
[...]

Then we can compile the tmp.s into a tmp.o

  gcc -c tmp.s -o tmp.o

And link it into back into main.o.

  ld -r main.o tmp.o -o tmp_main.o
  mv tmp_main.o main.o

But we have a problem.  What happens if the first function in a section
is not exported, and is a static function. The linker will not let
the tmp.o use it.  This case exists in main.o as well.

Disassembly of section .init.text:

0000000000000000 <set_reset_devices>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   e8 00 00 00 00          callq  9 <set_reset_devices+0x9>
                        5: R_X86_64_PC32        mcount+0xfffffffffffffffc

The first function in .init.text is a static function.

00000000000000a8 t __setup_set_reset_devices
000000000000105f t __setup_str_set_reset_devices
0000000000000000 t set_reset_devices

The lowercase 't' means that set_reset_devices is local and is not exported.
If we simply try to link the tmp.o with the set_reset_devices we end
up with two symbols: one local and one global.

 .section __mcount_loc,"a",@progbits
 .quad set_reset_devices + 0x10

00000000000000a8 t __setup_set_reset_devices
000000000000105f t __setup_str_set_reset_devices
0000000000000000 t set_reset_devices
                 U set_reset_devices

We still have an undefined reference to set_reset_devices, and if we try
to compile the kernel, we will end up with an undefined reference to
set_reset_devices, or even worst, it could be exported someplace else,
and then we will have a reference to the wrong location.

To handle this case, we make an intermediate step using objcopy.
We convert set_reset_devices into a global exported symbol before linking
it with tmp.o and set it back afterwards.

00000000000000a8 t __setup_set_reset_devices
000000000000105f t __setup_str_set_reset_devices
0000000000000000 T set_reset_devices

00000000000000a8 t __setup_set_reset_devices
000000000000105f t __setup_str_set_reset_devices
0000000000000000 T set_reset_devices

00000000000000a8 t __setup_set_reset_devices
000000000000105f t __setup_str_set_reset_devices
0000000000000000 t set_reset_devices

Now we have a section in main.o called __mcount_loc that we can place
somewhere in the kernel using vmlinux.ld.S and access it to convert
all these locations that call mcount into nops before starting SMP
and thus, eliminating the need to do this with kstop_machine.

Note, A well documented perl script (scripts/recordmcount.pl) is used
to do all this in one location.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14 10:34:40 +02:00
..
irq Merge branch 'linus' into x86/core 2008-08-14 14:58:01 +02:00
power ftrace: disable tracing for hibernation 2008-08-28 12:27:39 -07:00
time [CPUFREQ][5/6] cpufreq: Changes to get_cpu_idle_time_us(), used by ondemand governor 2008-10-09 13:52:44 -04:00
trace ftrace: create __mcount_loc section 2008-10-14 10:34:40 +02:00
.gitignore Update kernel/.gitignore with new auto-generated files 2008-02-09 23:27:01 -08:00
acct.c tty: Fix abusers of current->sighand->tty 2008-10-13 09:51:42 -07:00
audit_tree.c [PATCH] list_for_each_rcu must die: audit 2008-05-17 03:30:23 -04:00
audit.c [PATCH] Fix the bug of using AUDIT_STATUS_RATE_LIMIT when set fail, no error output. 2008-08-01 12:15:16 -04:00
audit.h [PATCH 1/2] audit: move extern declarations to audit.h 2008-04-28 06:28:04 -04:00
auditfilter.c Re: [PATCH] the loginuid field should be output in all AUDIT_CONFIG_CHANGE audit messages 2008-08-01 12:15:03 -04:00
auditsc.c tty: Fix abusers of current->sighand->tty 2008-10-13 09:51:42 -07:00
backtracetest.c backtrace: replace timer with tasklet + completions 2008-06-27 18:09:16 +02:00
bounds.c Add kbuild.h that contains common definitions for kbuild users 2008-04-29 08:06:29 -07:00
capability.c security: Fix setting of PF_SUPERPRIV by __capable() 2008-08-14 22:59:43 +10:00
cgroup_debug.c CGroup API files: move "releasable" to cgroup_debug subsystem 2008-04-29 08:06:09 -07:00
cgroup.c mm owner: fix race between swapoff and exit 2008-09-29 08:41:47 -07:00
compat.c ntp: support for TAI 2008-05-01 08:03:59 -07:00
configs.c kernel: use non-racy method for proc entries creation 2008-04-29 08:06:22 -07:00
cpu.c Merge branches 'sched/devel', 'sched/cpu-hotplug', 'sched/cpusets' and 'sched/urgent' into sched/core 2008-10-08 11:31:02 +02:00
cpuset.c cpusets: scan_for_empty_cpusets(), cpuset doesn't seem to be so const 2008-10-03 13:39:50 +02:00
delayacct.c per-task-delay-accounting: update taskstats for memory reclaim delay 2008-07-25 10:53:47 -07:00
dma-coherent.c dma-coherent: export dma_[alloc|release]_from_coherent methods 2008-08-22 08:34:53 +02:00
dma.c kernel: use non-racy method for proc entries creation 2008-04-29 08:06:22 -07:00
exec_domain.c [PATCH] kill altroot 2008-07-26 20:53:20 -04:00
exit.c tracing, sched: LTTng instrumentation - scheduler 2008-10-14 10:30:52 +02:00
extable.c module: Don't report discarded init pages as kernel text. 2008-01-29 17:13:18 +11:00
fork.c tracing, sched: LTTng instrumentation - scheduler 2008-10-14 10:30:52 +02:00
futex_compat.c futex_compat __user annotation 2008-03-30 14:18:41 -07:00
futex.c futexes: fix fault handling in futex_lock_pi 2008-06-23 13:31:15 +02:00
hrtimer.c hrtimer: prevent migration of per CPU hrtimers 2008-09-29 17:09:14 +02:00
itimer.c ITIMER_REAL: convert to use struct pid 2008-02-08 09:22:29 -08:00
kallsyms.c kallsyms: fix potential overflow in binary search 2008-07-25 10:53:27 -07:00
Kconfig.hz sched: fix SCHED_HRTICK dependency 2008-07-28 14:37:38 +02:00
Kconfig.preempt rcu: move PREEMPT_RCU config option back under PREEMPT 2008-03-10 18:01:20 -07:00
kexec.c kexec: fix segmentation fault in kimage_add_entry 2008-09-23 08:09:14 -07:00
kfifo.c
kgdb.c kgdb: call touch_softlockup_watchdog on resume 2008-10-06 13:50:59 -05:00
kmod.c call_usermodehelper(): increase reliability 2008-07-25 10:53:28 -07:00
kprobes.c kprobes: remove redundant config check 2008-07-25 10:53:30 -07:00
ksysfs.c Kobject: convert remaining kobject_unregister() to kobject_put() 2008-01-24 20:40:40 -08:00
kthread.c tracing, sched: LTTng instrumentation - scheduler 2008-10-14 10:30:52 +02:00
latencytop.c kernel: use non-racy method for proc entries creation 2008-04-29 08:06:22 -07:00
lockdep_internals.h lockdep: build fix 2008-08-13 12:55:10 +02:00
lockdep_proc.c lockstat: fix numerical output rounding error 2008-08-26 10:37:46 +02:00
lockdep.c lockdep: fix invalid list_del_rcu in zap_class 2008-08-27 08:40:36 +02:00
Makefile tracing: Kernel Tracepoints 2008-10-14 10:28:28 +02:00
marker.c markers: fix markers read barrier for multiple probes 2008-07-30 09:41:45 -07:00
module.c tracing: Kernel Tracepoints 2008-10-14 10:28:28 +02:00
mutex-debug.c mutex-debug: check mutex magic before owner 2008-05-16 16:53:35 +02:00
mutex-debug.h
mutex.c locking: fix mutex @key parameter kernel-doc notation 2008-07-28 18:12:36 +02:00
mutex.h
notifier.c ftrace: ignore functions that cannot be kprobe-ed 2008-10-14 10:34:22 +02:00
ns_cgroup.c cgroup_clone: use pid of newly created task for new cgroup 2008-07-25 10:53:37 -07:00
nsproxy.c removed unused #include <linux/version.h>'s 2008-08-23 12:14:12 -07:00
panic.c Add a WARN() macro; this is WARN_ON() + printk arguments 2008-07-25 10:53:29 -07:00
params.c Add new string functions strict_strto* and convert kernel params to use them 2008-02-08 09:22:41 -08:00
pid_namespace.c pid_ns: (BUG 11391) change ->child_reaper when init->group_leader exits 2008-09-02 19:21:38 -07:00
pid.c pidns: remove now unused find_pid function. 2008-07-25 10:53:45 -07:00
pm_qos_params.c pm_qos_requirement might sleep 2008-09-02 19:21:40 -07:00
posix-cpu-timers.c posix-timers: print RT watchdog message 2008-05-24 18:49:22 +02:00
posix-timers.c fix error-path NULL deref in alloc_posix_timer() 2008-10-02 15:53:13 -07:00
printk.c tty: Move tty_write_message out of kernel/printk 2008-10-13 09:51:41 -07:00
profile.c build kernel/profile.o only when requested 2008-07-25 10:53:27 -07:00
ptrace.c security: Fix setting of PF_SUPERPRIV by __capable() 2008-08-14 22:59:43 +10:00
rcuclassic.c rcu: RCU-based detection of stalled CPUs for Classic RCU, fix 2008-10-03 10:41:00 +02:00
rcupdate.c rcu: fix synchronize_rcu() so that kernel-doc works 2008-08-21 09:31:44 +02:00
rcupreempt_trace.c rcu: trace fix possible mem-leak 2008-08-15 17:54:40 +02:00
rcupreempt.c rcu: remove redundant ACCESS_ONCE definition from rcupreempt.c 2008-08-18 09:45:22 +02:00
rcutorture.c rcu: make rcutorture even more vicious: invoke RCU readers from irq handlers (timers) 2008-06-26 09:24:33 +02:00
relay.c relay: fix "full buffer with exactly full last subbuffer" accounting problem 2008-08-05 14:33:46 -07:00
res_counter.c cgroup files: convert res_counter_write() to be a cgroups write_string() handler 2008-07-25 10:53:36 -07:00
resource.c IO resources: add reserve_region_with_split() 2008-09-04 21:02:44 +02:00
rtmutex_common.h Don't operate with pid_t in rtmutex tester 2008-02-08 09:22:41 -08:00
rtmutex-debug.c Don't operate with pid_t in rtmutex tester 2008-02-08 09:22:41 -08:00
rtmutex-debug.h
rtmutex-tester.c sysdev: Pass the attribute to the low level sysdev show/store function 2008-07-21 21:55:02 -07:00
rtmutex.c hrtimer: more hrtimer_init_sleeper() fallout. 2008-02-13 15:45:36 +01:00
rtmutex.h
rwsem.c sched: mark rwsem functions as __sched for wchan/profiling 2007-12-18 15:21:13 +01:00
sched_clock.c sched_clock: fix cpu_clock() 2008-08-25 17:39:57 +02:00
sched_cpupri.c sched: use a 2-d bitmap for searching lowest-pri CPU 2008-06-06 15:19:28 +02:00
sched_cpupri.h sched: fix the cpuprio count really 2008-06-06 15:19:44 +02:00
sched_debug.c sched: add full schedstats to /proc/sched_debug 2008-06-27 14:31:31 +02:00
sched_fair.c sched: sync wakeups vs avg_overlap 2008-10-08 12:20:26 +02:00
sched_features.h sched: turn off WAKEUP_OVERLAP 2008-09-22 16:29:00 +02:00
sched_idletask.c sched: wakeup preempt when small overlap 2008-09-22 16:28:32 +02:00
sched_rt.c sched_rt.c: resch needed in rt_rq_enqueue() for the root rt_rq 2008-10-04 14:31:54 +02:00
sched_stats.h sched: fix accounting in task delay accounting & migration 2008-07-04 12:50:23 +02:00
sched.c tracing, sched: LTTng instrumentation - scheduler 2008-10-14 10:30:52 +02:00
seccomp.c
semaphore.c semaphore: __down_common: use signal_pending_state() 2008-08-05 14:33:47 -07:00
signal.c tracing, sched: LTTng instrumentation - scheduler 2008-10-14 10:30:52 +02:00
smp.c smp: have smp_call_function_single() detect invalid CPUs 2008-08-25 17:45:48 -07:00
softirq.c Full conversion to early_initcall() interface, remove old interface 2008-07-26 12:00:04 -07:00
softlockup.c softlockup: minor cleanup, don't check task->state twice 2008-09-02 10:49:51 -07:00
spinlock.c lockdep: spin_lock_nest_lock(), checkpatch fixes 2008-08-13 13:56:51 +02:00
srcu.c make srcu_readers_active() static 2008-02-06 10:41:02 -08:00
stacktrace.c stacktrace: fix modular build, export print_stack_trace and save_stack_trace 2008-06-30 09:20:55 +02:00
stop_machine.c stop_machine: remove unused variable 2008-08-12 17:52:55 +10:00
sys_ni.c signalfd: fix undefined reference to `compat_sys_signalfd4' when !CONFIG_SIGNALFD 2008-07-25 11:35:41 -07:00
sys.c tty: Add a kref count 2008-10-13 09:51:40 -07:00
sysctl_check.c sysctl: check for bogus modes 2008-07-25 10:53:45 -07:00
sysctl.c Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/sparc-2.6 2008-09-16 14:11:43 -07:00
taskstats.c taskstats: remove initialization of static per-cpu variable 2008-07-25 10:53:47 -07:00
test_kprobes.c kprobes: kretprobe user entry-handler 2008-02-06 10:41:11 -08:00
time.c Make constants in kernel/timeconst.h fixed 64 bits 2008-05-02 16:18:42 -07:00
timeconst.pl Make constants in kernel/timeconst.h fixed 64 bits 2008-05-02 16:18:42 -07:00
timer.c Merge branch 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-07-14 16:06:58 -07:00
tracepoint.c tracepoints: use TABLE_SIZE macro 2008-10-14 10:34:07 +02:00
tsacct.c task IO accounting: move all IO statistics in struct task_io_accounting 2008-07-27 16:12:28 -07:00
uid16.c asmlinkage_protect replaces prevent_tail_call 2008-04-10 17:28:26 -07:00
user_namespace.c removed unused #include <linux/version.h>'s 2008-08-23 12:14:12 -07:00
user.c sched: rt-bandwidth for user grouping interface 2008-08-19 13:10:09 +02:00
utsname_sysctl.c removed unused #include <linux/version.h>'s 2008-08-23 12:14:12 -07:00
utsname.c removed unused #include <linux/version.h>'s 2008-08-23 12:14:12 -07:00
wait.c kernel: remove fastcall in kernel/* 2008-02-08 09:22:31 -08:00
workqueue.c Merge branch 'core/locking' into core/urgent 2008-08-12 00:11:49 +02:00