linux-toradex.git/arch/x86/kernel/mcount_64.S, branch v4.4.86

ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it

2017-01-26T07:23:46+00:00

commit 8329e818f14926a6040df86b2668568bde342ebf upstream.

Matt Fleming reported seeing crashes when enabling and disabling
function profiling which uses function graph tracer. Later Namhyung Kim
hit a similar issue and he found that the issue was due to the jmp to
ftrace_stub in ftrace_graph_call was only two bytes, and when it was
changed to jump to the tracing code, it overwrote the ftrace_stub that
was after it.

Masami Hiramatsu bisected this down to a binutils change:

8dcea93252a9ea7dff57e85220a719e2a5e8ab41 is the first bad commit
commit 8dcea93252a9ea7dff57e85220a719e2a5e8ab41
Author: H.J. Lu 
Date:   Fri May 15 03:17:31 2015 -0700

    Add -mshared option to x86 ELF assembler

    This patch adds -mshared option to x86 ELF assembler.  By default,
    assembler will optimize out non-PLT relocations against defined non-weak
    global branch targets with default visibility.  The -mshared option tells
    the assembler to generate code which may go into a shared library
    where all non-weak global branch targets with default visibility can
    be preempted.  The resulting code is slightly bigger.  This option
    only affects the handling of branch instructions.

Declaring ftrace_stub as a weak call prevents gas from using two byte
jumps to it, which would be converted to a jump to the function graph
code.

Link: http://lkml.kernel.org/r/20160516230035.1dbae571@gandalf.local.home

Reported-by: Matt Fleming 
Reported-by: Namhyung Kim 
Tested-by: Matt Fleming 
Reviewed-by: Masami Hiramatsu 
Signed-off-by: Steven Rostedt 
Cc: Jiri Slaby 
Signed-off-by: Greg Kroah-Hartman

x86/ftrace: Add comment on static function tracing

2015-11-19T10:07:49+00:00

There was a confusion between update_ftrace_function() and static
function tracing trampoline regarding 3rd parameter (ftrace_ops).
Add a comment for clarification.

Suggested-by: Steven Rostedt 
Signed-off-by: Namhyung Kim 
Cc: H. Peter Anvin 
Cc: Steven Rostedt 
Link: http://lkml.kernel.org/r/1447721004-2551-1-git-send-email-namhyung@kernel.org
Signed-off-by: Thomas Gleixner

ftrace/fgraph/x86: Have prepare_ftrace_return() take ip as first parameter

2014-12-01T19:08:58+00:00

The function graph helper function prepare_ftrace_return() which does the work
to hijack the parent pointer has that parent pointer as its first parameter.
Instead, if we make it the second parameter and have ip as the first parameter
(self_addr), then it can use the %rdi from save_mcount_regs that loads it
already.

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Signed-off-by: Steven Rostedt

ftrace/x86: Get rid of ftrace_caller_setup

2014-12-01T19:08:43+00:00

Move all the work from ftrace_caller_setup into save_mcount_regs. This
simplifies the code and makes it easier to understand.

Link: http://lkml.kernel.org/r/CA+55aFxUTUbdxpjVMW8X9c=o8sui7OB_MYPfcbJuDyfUWtNrNg@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Suggested-by: Linus Torvalds 
Signed-off-by: Steven Rostedt

ftrace/x86: Have save_mcount_regs macro also save stack frames if needed

2014-12-01T19:08:27+00:00

The save_mcount_regs macro saves and restores the required mcount regs that
need to be saved before calling C code. It is done for all the function hook
utilities (static tracing, dynamic tracing, regs, function graph).

When frame pointers are enabled, the ftrace trampolines need to set up
frames and pointers such that a back trace (dump stack) can continue passed
them. Currently, a separate macro is used (create_frame) to do this, but
it's only done for the ftrace_caller and ftrace_reg_caller functions. It
is not done for the static tracer or function graph tracing.

Instead of having a separate macro doing the recording of the frames,
have the save_mcount_regs perform this task. This also has all tracers
saving the frame pointers when needed.

Link: http://lkml.kernel.org/r/CA+55aFwF+qCGSKdGaEgW4p6N65GZ5_XTV=1NbtWDvxnd5yYLiw@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Suggested-by: Linus Torvalds 
Signed-off-by: Steven Rostedt

ftrace/x86: Add macro MCOUNT_REG_SIZE for amount of stack used to save mcount regs

2014-12-01T19:08:15+00:00

The macro save_mcount_regs saves regs onto the stack. But to uncouple the
amount of stack used in that macro from the users of the macro, we need
to have a define that tells all the users how much stack is used by that
macro. This way we can change the amount of stack the macro uses without
breaking its users.

Also remove some dead code that was left over from commit fdc841b58cf5
"ftrace: x86: Remove check of obsolete variable function_trace_stop".

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Signed-off-by: Steven Rostedt

ftrace/x86: Simplify save_mcount_regs on getting RIP

2014-12-01T19:07:50+00:00

Currently save_mcount_regs is passed a "skip" parameter to know how much
stack updated the pt_regs, as it tries to keep the saved pt_regs in the
same location for all users. This is rather stupid, especially since the
part stored on the pt_regs has nothing to do with what is suppose to be
in that location.

Instead of doing that, just pass in an "added" parameter that lets that
macro know how much stack was added before it was called so that it
can get to the RIP.  But the difference is that it will now offset the
pt_regs by that "added" count. The caller now needs to take care of
the offset of the pt_regs.

This will make it easier to simplify the code later.

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Signed-off-by: Steven Rostedt

ftrace/x86: Have save_mcount_regs store RIP in %rdi for first parameter

2014-12-01T19:07:39+00:00

Instead of having save_mcount_regs store the RIP in %rdx as a temp register
to place it in the proper location of the pt_regs on the stack. Use the
%rdi register as the temp register. This lets us remove the extra store
in the ftrace_caller_setup macro.

Link: http://lkml.kernel.org/r/CA+55aFwF+qCGSKdGaEgW4p6N65GZ5_XTV=1NbtWDvxnd5yYLiw@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Suggested-by: Linus Torvalds 
Signed-off-by: Steven Rostedt

ftrace/x86: Rename MCOUNT_SAVE_FRAME and add more detailed comments

2014-12-01T19:07:27+00:00

The name MCOUNT_SAVE_FRAME is rather confusing as it really isn't a
function frame that is saved, but just the required mcount registers
that are needed to be saved before C code may be called. The word
"frame" confuses it as being a function frame which it is not.

Rename MCOUNT_SAVE_FRAME and MCOUNT_RESTORE_FRAME to save_mcount_regs
and restore_mcount_regs respectively. Noticed the lower case, which
keeps it from screaming at the reviewers.

Link: http://lkml.kernel.org/r/CA+55aFwF+qCGSKdGaEgW4p6N65GZ5_XTV=1NbtWDvxnd5yYLiw@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Signed-off-by: Steven Rostedt

ftrace/x86: Move MCOUNT_SAVE_FRAME out of header file

2014-12-01T19:07:16+00:00

Linus pointed out that MCOUNT_SAVE_FRAME is used in only a single file
and that there's no reason that it should be in a header file.
Move the macro to the code that uses it.

Link: http://lkml.kernel.org/r/CA+55aFwF+qCGSKdGaEgW4p6N65GZ5_XTV=1NbtWDvxnd5yYLiw@mail.gmail.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1411262304010.3961@nanos

Reviewed-by: Thomas Gleixner 
Signed-off-by: Steven Rostedt