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Subject[tip:x86/pti] x86/entry/64: Fix paranoid_entry() frame pointer warning
Commit-ID:  b3ccefaed922529e6a67de7b30af5aa38c76ace9
Gitweb: https://git.kernel.org/tip/b3ccefaed922529e6a67de7b30af5aa38c76ace9
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Mon, 12 Feb 2018 11:45:03 -0600
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 13 Feb 2018 09:04:55 +0100

x86/entry/64: Fix paranoid_entry() frame pointer warning

With the following commit:

f09d160992d1 ("x86/entry/64: Get rid of the ALLOC_PT_GPREGS_ON_STACK and SAVE_AND_CLEAR_REGS macros")

... one of my suggested improvements triggered a frame pointer warning:

arch/x86/entry/entry_64.o: warning: objtool: paranoid_entry()+0x11: call without frame pointer save/setup

The warning is correct for the build-time code, but it's actually not
relevant at runtime because of paravirt patching. The paravirt swapgs
call gets replaced with either a SWAPGS instruction or NOPs at runtime.

Go back to the previous behavior by removing the ELF function annotation
for paranoid_entry() and adding an unwind hint, which effectively
silences the warning.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kbuild-all@01.org
Cc: tipbuild@zytor.com
Fixes: f09d160992d1 ("x86/entry/64: Get rid of the ALLOC_PT_GPREGS_ON_STACK and SAVE_AND_CLEAR_REGS macros")
Link: http://lkml.kernel.org/r/20180212174503.5acbymg5z6p32snu@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/entry/entry_64.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index cfbf433..1c5420420 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1128,6 +1128,7 @@ idtentry machine_check do_mce has_error_code=0 paranoid=1
* Return: ebx=0: need swapgs on exit, ebx=1: otherwise
*/
ENTRY(paranoid_entry)
+ UNWIND_HINT_FUNC
cld
movl $1, %ebx
movl $MSR_GS_BASE, %ecx
@@ -1141,7 +1142,7 @@ ENTRY(paranoid_entry)
SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14

ret
-ENDPROC(paranoid_entry)
+END(paranoid_entry)

/*
* "Paranoid" exit path from exception stack. This is invoked
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