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[tip:core/urgent] objtool, drm/vmwgfx: Fix "duplicate frame pointer save" warning

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Commit-ID:  0b0d81e3b7334897da9b2e3ffee860c2046f7bc0
Gitweb:     http://git.kernel.org/tip/0b0d81e3b7334897da9b2e3ffee860c2046f7bc0
Author:     Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Thu, 26 May 2016 13:43:43 -0500
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 8 Jun 2016 15:36:18 +0200

objtool, drm/vmwgfx: Fix "duplicate frame pointer save" warning

objtool reports the following warnings:

  drivers/gpu/drm/vmwgfx/vmwgfx_msg.o: warning: objtool: vmw_send_msg()+0x107: duplicate frame pointer save
  drivers/gpu/drm/vmwgfx/vmwgfx_msg.o: warning: objtool: vmw_host_get_guestinfo()+0x252: duplicate frame pointer save

To quote Linus:

 "The reason is that VMW_PORT_HB_OUT() uses a magic instruction sequence
  (a "rep outsb") to communicate with the hypervisor (it's a virtual GPU
  driver for vmware), and %rbp is part of the communication. So the
  inline asm does a save-and-restore of the frame pointer around the
  instruction sequence.

  I actually find the objtool warning to be quite reasonable, so it's
  not exactly a false positive, since in this case it actually does
  point out that the frame pointer won't be reliable over that
  instruction sequence.

  But in this particular case it just ends up being the wrong thing -
  the code is what it is, and %rbp just can't have the frame information
  due to annoying magic calling conventions."

Silence the warnings by telling objtool to ignore the two functions
which use the VMW_PORT_HB_{IN,OUT} macros.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: DRI <dri-devel@lists.freedesktop.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160526184343.fdtjjjg67smmeekt@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_msg.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c b/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
index 6de283c..f0374f9 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/frame.h>
 #include <asm/hypervisor.h>
 #include "drmP.h"
 #include "vmwgfx_msg.h"
@@ -194,7 +195,7 @@ static int vmw_send_msg(struct rpc_channel *channel, const char *msg)
 
 	return -EINVAL;
 }
-
+STACK_FRAME_NON_STANDARD(vmw_send_msg);
 
 
 /**
@@ -304,6 +305,7 @@ static int vmw_recv_msg(struct rpc_channel *channel, void **msg,
 
 	return 0;
 }
+STACK_FRAME_NON_STANDARD(vmw_recv_msg);
 
 
 /**

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[tip:core/urgent] objtool, drm/vmwgfx: Fix "duplicate frame pointer  save" warning tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-06-08 16:30 +0200

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