linux-kernel - [PATCH 0/6] [GIT PULL] ftrace/x86: Ftrace cleanup and add support for -mfentry on x86

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Date:   Tue, 21 Mar 2017 21:35:02 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 0/6] [GIT PULL] ftrace/x86: Ftrace cleanup and add support for -mfentry on x86_32

[
 Ingo, Thomas or H.Peter,

 I believe this is all set to go now. I updated those patches that Linus
 commented on and I don't believe there are any more issues. I ran this
 through several tests (although some of my tests are failing due to
 bugs introduced by others in 4.11-rc2). You can take this as a patch
 series, or you can pull from my tree defined below. It's based on 4.11-rc2
 as I noticed that tip/x86/core is rather outdated, and Linus is fine with
 basing off of his tagged releases.
]

With the issues of gcc screwing around with the mcount stack frame causing
function graph tracer to panic on x86_32, and with Linus saying that we
should start deprecating mcount (at least on x86), I figured that x86_32
needs to support fentry.

First, I renamed mcount_64.S to ftrace_64.S. As we want to get away from
mcount, having the ftrace code in a file called mcount seems rather backwards.

Next I moved the ftrace code out of entry_32.S. It's not in entry_64.S
and it does not belong in entry_32.S.

I noticed that the x86_32 code has the same issue as the x86_64 did
in the past with respect to a stack frame. I fixed that just for the main
ftrace_caller. The ftrace_regs_caller is rather special, and so is
function graph tracing.

I realized the ftrace_regs_caller code was complex due to me aggressively
saving flags, even though I could still do push, lea and mov without
changing them. That made the logic a little nicer.

Finally I added the fentry code.

I tested this with an older compiler (for mcount) with and without
FRAME_POINTER set. I also did it with a new compiler (with fentry), with and
without FRAME_POINTER. I tested function tracing, stack tracing, function_graph
tracing, and kprobes (as that uses the ftrace_regs_caller).

Please pull (or take the patch series) from:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/x86/ftrace

Head SHA1: e086b1da846b8e53f4de11e38d02d05b1ec5db58

Steven Rostedt (VMware) (6):
      ftrace/x86_64: Rename mcount_64.S to ftrace_64.S
      ftrace/x86_32: Move the ftrace specific code out of entry_32.S
      ftrace/x86_32: Add stack frame pointer to ftrace_caller
      ftrace/x86_32: Clean up ftrace_regs_caller
      ftrace/x86_32: Add -mfentry support to x86_32 with DYNAMIC_FTRACE set
      ftrace/x86: Use Makefile logic instead of #ifdef for compiling ftrace_*.o

----
Changes since v3:

  * Changed comment about regs being skipped (Josh Poimboeuf)

  * Change subject line to fix typo (Josh Poimboeuf)

 arch/x86/Kconfig                             |   2 +-
 arch/x86/entry/entry_32.S                    | 169 ------------------
 arch/x86/kernel/Makefile                     |   5 +-
 arch/x86/kernel/ftrace_32.S                  | 246 +++++++++++++++++++++++++++
 arch/x86/kernel/{mcount_64.S => ftrace_64.S} |   4 -
 5 files changed, 250 insertions(+), 176 deletions(-)
 create mode 100644 arch/x86/kernel/ftrace_32.S
 rename arch/x86/kernel/{mcount_64.S => ftrace_64.S} (99%)

Diff against v3:

diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 4d52e0d49e26..de50c9084d16 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -167,7 +167,7 @@ GLOBAL(ftrace_regs_call)
 	popl	%gs

 	/* use lea to not affect flags */
-	lea	3*4(%esp), %esp			/* Skip orig_ax, ip and flags */
+	lea	3*4(%esp), %esp			/* Skip orig_ax, ip and cs */

 	jmp	.Lftrace_ret
 #else /* ! CONFIG_DYNAMIC_FTRACE */