linux/tools/objtool/cfi.h
Josh Poimboeuf dd88a0a0c8 objtool: Handle GCC stack pointer adjustment bug
Arnd Bergmann reported the following warning with GCC 7.1.1:

  fs/fs_pin.o: warning: objtool: pin_kill()+0x139: stack state mismatch: cfa1=7+88 cfa2=7+96

And the kbuild robot reported the following warnings with GCC 5.4.1:

  fs/fs_pin.o: warning: objtool: pin_kill()+0x182: return with modified stack frame
  fs/quota/dquot.o: warning: objtool: dquot_alloc_inode()+0x140: stack state mismatch: cfa1=7+120 cfa2=7+128
  fs/quota/dquot.o: warning: objtool: dquot_free_inode()+0x11a: stack state mismatch: cfa1=7+112 cfa2=7+120

Those warnings are caused by an unusual GCC non-optimization where it
uses an intermediate register to adjust the stack pointer.  It does:

  lea    0x8(%rsp), %rcx
  ...
  mov    %rcx, %rsp

Instead of the obvious:

  add    $0x8, %rsp

It makes no sense to use an intermediate register, so I opened a GCC bug
to track it:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81813

But it's not exactly a high-priority bug and it looks like we'll be
stuck with this issue for a while.  So for now we have to track register
values when they're loaded with stack pointer offsets.

This is kind of a big workaround for a tiny problem, but c'est la vie.
I hope to eventually create a GCC plugin to implement a big chunk of
objtool's functionality.  Hopefully at that point we'll be able to
remove of a lot of these GCC-isms from the objtool code.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/6a41a96884c725e7f05413bb7df40cfe824b2444.1504028945.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-08-30 10:48:41 +02:00

56 lines
1.4 KiB
C

/*
* Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#ifndef _OBJTOOL_CFI_H
#define _OBJTOOL_CFI_H
#define CFI_UNDEFINED -1
#define CFI_CFA -2
#define CFI_SP_INDIRECT -3
#define CFI_BP_INDIRECT -4
#define CFI_AX 0
#define CFI_DX 1
#define CFI_CX 2
#define CFI_BX 3
#define CFI_SI 4
#define CFI_DI 5
#define CFI_BP 6
#define CFI_SP 7
#define CFI_R8 8
#define CFI_R9 9
#define CFI_R10 10
#define CFI_R11 11
#define CFI_R12 12
#define CFI_R13 13
#define CFI_R14 14
#define CFI_R15 15
#define CFI_RA 16
#define CFI_NUM_REGS 17
struct cfi_reg {
int base;
int offset;
};
struct cfi_state {
struct cfi_reg cfa;
struct cfi_reg regs[CFI_NUM_REGS];
};
#endif /* _OBJTOOL_CFI_H */